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Diffstat (limited to 'src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java')
| -rw-r--r-- | src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java | 3022 |
1 files changed, 1369 insertions, 1653 deletions
diff --git a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java b/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java index 401ce6c5c9..3fad92cbf1 100644 --- a/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java +++ b/src/forkjoin/scala/concurrent/forkjoin/ForkJoinPool.java @@ -1,370 +1,107 @@ /* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at - * http://creativecommons.org/publicdomain/zero/1.0/ + * http://creativecommons.org/licenses/publicdomain */ package scala.concurrent.forkjoin; - -import java.util.ArrayList; -import java.util.Arrays; -import java.util.Collection; -import java.util.Collections; -import java.util.List; -import java.util.Random; -import java.util.concurrent.AbstractExecutorService; -import java.util.concurrent.Callable; -import java.util.concurrent.ExecutorService; -import java.util.concurrent.Future; -import java.util.concurrent.RejectedExecutionException; -import java.util.concurrent.RunnableFuture; -import java.util.concurrent.TimeUnit; -import java.util.concurrent.TimeoutException; -import java.util.concurrent.atomic.AtomicInteger; -import java.util.concurrent.locks.LockSupport; -import java.util.concurrent.locks.ReentrantLock; -import java.util.concurrent.locks.Condition; +import java.util.*; +import java.util.concurrent.*; +import java.util.concurrent.locks.*; +import java.util.concurrent.atomic.*; +import sun.misc.Unsafe; +import java.lang.reflect.*; /** - * An {@link ExecutorService} for running {@link ForkJoinTask}s. - * A {@code ForkJoinPool} provides the entry point for submissions - * from non-{@code ForkJoinTask} clients, as well as management and - * monitoring operations. + * An {@link ExecutorService} for running {@link ForkJoinTask}s. A + * ForkJoinPool provides the entry point for submissions from + * non-ForkJoinTasks, as well as management and monitoring operations. + * Normally a single ForkJoinPool is used for a large number of + * submitted tasks. Otherwise, use would not usually outweigh the + * construction and bookkeeping overhead of creating a large set of + * threads. * - * <p>A {@code ForkJoinPool} differs from other kinds of {@link - * ExecutorService} mainly by virtue of employing - * <em>work-stealing</em>: all threads in the pool attempt to find and - * execute subtasks created by other active tasks (eventually blocking - * waiting for work if none exist). This enables efficient processing - * when most tasks spawn other subtasks (as do most {@code - * ForkJoinTask}s). When setting <em>asyncMode</em> to true in - * constructors, {@code ForkJoinPool}s may also be appropriate for use - * with event-style tasks that are never joined. + * <p>ForkJoinPools differ from other kinds of Executors mainly in + * that they provide <em>work-stealing</em>: all threads in the pool + * attempt to find and execute subtasks created by other active tasks + * (eventually blocking if none exist). This makes them efficient when + * most tasks spawn other subtasks (as do most ForkJoinTasks), as well + * as the mixed execution of some plain Runnable- or Callable- based + * activities along with ForkJoinTasks. When setting + * <tt>setAsyncMode</tt>, a ForkJoinPools may also be appropriate for + * use with fine-grained tasks that are never joined. Otherwise, other + * ExecutorService implementations are typically more appropriate + * choices. * - * <p>A {@code ForkJoinPool} is constructed with a given target - * parallelism level; by default, equal to the number of available - * processors. The pool attempts to maintain enough active (or - * available) threads by dynamically adding, suspending, or resuming - * internal worker threads, even if some tasks are stalled waiting to - * join others. However, no such adjustments are guaranteed in the - * face of blocked IO or other unmanaged synchronization. The nested - * {@link ManagedBlocker} interface enables extension of the kinds of - * synchronization accommodated. + * <p>A ForkJoinPool may be constructed with a given parallelism level + * (target pool size), which it attempts to maintain by dynamically + * adding, suspending, or resuming threads, even if some tasks are + * waiting to join others. However, no such adjustments are performed + * in the face of blocked IO or other unmanaged synchronization. The + * nested <code>ManagedBlocker</code> interface enables extension of + * the kinds of synchronization accommodated. The target parallelism + * level may also be changed dynamically (<code>setParallelism</code>) + * and thread construction can be limited using methods + * <code>setMaximumPoolSize</code> and/or + * <code>setMaintainsParallelism</code>. * * <p>In addition to execution and lifecycle control methods, this * class provides status check methods (for example - * {@link #getStealCount}) that are intended to aid in developing, + * <code>getStealCount</code>) that are intended to aid in developing, * tuning, and monitoring fork/join applications. Also, method - * {@link #toString} returns indications of pool state in a + * <code>toString</code> returns indications of pool state in a * convenient form for informal monitoring. * - * <p> As is the case with other ExecutorServices, there are three - * main task execution methods summarized in the following - * table. These are designed to be used by clients not already engaged - * in fork/join computations in the current pool. The main forms of - * these methods accept instances of {@code ForkJoinTask}, but - * overloaded forms also allow mixed execution of plain {@code - * Runnable}- or {@code Callable}- based activities as well. However, - * tasks that are already executing in a pool should normally - * <em>NOT</em> use these pool execution methods, but instead use the - * within-computation forms listed in the table. - * - * <table BORDER CELLPADDING=3 CELLSPACING=1> - * <tr> - * <td></td> - * <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> - * <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> - * </tr> - * <tr> - * <td> <b>Arrange async execution</td> - * <td> {@link #execute(ForkJoinTask)}</td> - * <td> {@link ForkJoinTask#fork}</td> - * </tr> - * <tr> - * <td> <b>Await and obtain result</td> - * <td> {@link #invoke(ForkJoinTask)}</td> - * <td> {@link ForkJoinTask#invoke}</td> - * </tr> - * <tr> - * <td> <b>Arrange exec and obtain Future</td> - * <td> {@link #submit(ForkJoinTask)}</td> - * <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> - * </tr> - * </table> - * - * <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is - * used for all parallel task execution in a program or subsystem. - * Otherwise, use would not usually outweigh the construction and - * bookkeeping overhead of creating a large set of threads. For - * example, a common pool could be used for the {@code SortTasks} - * illustrated in {@link RecursiveAction}. Because {@code - * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon - * daemon} mode, there is typically no need to explicitly {@link - * #shutdown} such a pool upon program exit. - * - * <pre> - * static final ForkJoinPool mainPool = new ForkJoinPool(); - * ... - * public void sort(long[] array) { - * mainPool.invoke(new SortTask(array, 0, array.length)); - * } - * </pre> - * * <p><b>Implementation notes</b>: This implementation restricts the * maximum number of running threads to 32767. Attempts to create - * pools with greater than the maximum number result in - * {@code IllegalArgumentException}. - * - * <p>This implementation rejects submitted tasks (that is, by throwing - * {@link RejectedExecutionException}) only when the pool is shut down - * or internal resources have been exhausted. - * - * @since 1.7 - * @author Doug Lea + * pools with greater than the maximum result in + * IllegalArgumentExceptions. */ public class ForkJoinPool /*extends AbstractExecutorService*/ { /* - * Implementation Overview - * - * This class provides the central bookkeeping and control for a - * set of worker threads: Submissions from non-FJ threads enter - * into a submission queue. Workers take these tasks and typically - * split them into subtasks that may be stolen by other workers. - * Preference rules give first priority to processing tasks from - * their own queues (LIFO or FIFO, depending on mode), then to - * randomized FIFO steals of tasks in other worker queues, and - * lastly to new submissions. - * - * The main throughput advantages of work-stealing stem from - * decentralized control -- workers mostly take tasks from - * themselves or each other. We cannot negate this in the - * implementation of other management responsibilities. The main - * tactic for avoiding bottlenecks is packing nearly all - * essentially atomic control state into a single 64bit volatile - * variable ("ctl"). This variable is read on the order of 10-100 - * times as often as it is modified (always via CAS). (There is - * some additional control state, for example variable "shutdown" - * for which we can cope with uncoordinated updates.) This - * streamlines synchronization and control at the expense of messy - * constructions needed to repack status bits upon updates. - * Updates tend not to contend with each other except during - * bursts while submitted tasks begin or end. In some cases when - * they do contend, threads can instead do something else - * (usually, scan for tasks) until contention subsides. - * - * To enable packing, we restrict maximum parallelism to (1<<15)-1 - * (which is far in excess of normal operating range) to allow - * ids, counts, and their negations (used for thresholding) to fit - * into 16bit fields. - * - * Recording Workers. Workers are recorded in the "workers" array - * that is created upon pool construction and expanded if (rarely) - * necessary. This is an array as opposed to some other data - * structure to support index-based random steals by workers. - * Updates to the array recording new workers and unrecording - * terminated ones are protected from each other by a seqLock - * (scanGuard) but the array is otherwise concurrently readable, - * and accessed directly by workers. To simplify index-based - * operations, the array size is always a power of two, and all - * readers must tolerate null slots. To avoid flailing during - * start-up, the array is presized to hold twice #parallelism - * workers (which is unlikely to need further resizing during - * execution). But to avoid dealing with so many null slots, - * variable scanGuard includes a mask for the nearest power of two - * that contains all current workers. All worker thread creation - * is on-demand, triggered by task submissions, replacement of - * terminated workers, and/or compensation for blocked - * workers. However, all other support code is set up to work with - * other policies. To ensure that we do not hold on to worker - * references that would prevent GC, ALL accesses to workers are - * via indices into the workers array (which is one source of some - * of the messy code constructions here). In essence, the workers - * array serves as a weak reference mechanism. Thus for example - * the wait queue field of ctl stores worker indices, not worker - * references. Access to the workers in associated methods (for - * example signalWork) must both index-check and null-check the - * IDs. All such accesses ignore bad IDs by returning out early - * from what they are doing, since this can only be associated - * with termination, in which case it is OK to give up. - * - * All uses of the workers array, as well as queue arrays, check - * that the array is non-null (even if previously non-null). This - * allows nulling during termination, which is currently not - * necessary, but remains an option for resource-revocation-based - * shutdown schemes. - * - * Wait Queuing. Unlike HPC work-stealing frameworks, we cannot - * let workers spin indefinitely scanning for tasks when none can - * be found immediately, and we cannot start/resume workers unless - * there appear to be tasks available. On the other hand, we must - * quickly prod them into action when new tasks are submitted or - * generated. We park/unpark workers after placing in an event - * wait queue when they cannot find work. This "queue" is actually - * a simple Treiber stack, headed by the "id" field of ctl, plus a - * 15bit counter value to both wake up waiters (by advancing their - * count) and avoid ABA effects. Successors are held in worker - * field "nextWait". Queuing deals with several intrinsic races, - * mainly that a task-producing thread can miss seeing (and - * signalling) another thread that gave up looking for work but - * has not yet entered the wait queue. We solve this by requiring - * a full sweep of all workers both before (in scan()) and after - * (in tryAwaitWork()) a newly waiting worker is added to the wait - * queue. During a rescan, the worker might release some other - * queued worker rather than itself, which has the same net - * effect. Because enqueued workers may actually be rescanning - * rather than waiting, we set and clear the "parked" field of - * ForkJoinWorkerThread to reduce unnecessary calls to unpark. - * (Use of the parked field requires a secondary recheck to avoid - * missed signals.) - * - * Signalling. We create or wake up workers only when there - * appears to be at least one task they might be able to find and - * execute. When a submission is added or another worker adds a - * task to a queue that previously had two or fewer tasks, they - * signal waiting workers (or trigger creation of new ones if - * fewer than the given parallelism level -- see signalWork). - * These primary signals are buttressed by signals during rescans - * as well as those performed when a worker steals a task and - * notices that there are more tasks too; together these cover the - * signals needed in cases when more than two tasks are pushed - * but untaken. - * - * Trimming workers. To release resources after periods of lack of - * use, a worker starting to wait when the pool is quiescent will - * time out and terminate if the pool has remained quiescent for - * SHRINK_RATE nanosecs. This will slowly propagate, eventually - * terminating all workers after long periods of non-use. - * - * Submissions. External submissions are maintained in an - * array-based queue that is structured identically to - * ForkJoinWorkerThread queues except for the use of - * submissionLock in method addSubmission. Unlike the case for - * worker queues, multiple external threads can add new - * submissions, so adding requires a lock. - * - * Compensation. Beyond work-stealing support and lifecycle - * control, the main responsibility of this framework is to take - * actions when one worker is waiting to join a task stolen (or - * always held by) another. Because we are multiplexing many - * tasks on to a pool of workers, we can't just let them block (as - * in Thread.join). We also cannot just reassign the joiner's - * run-time stack with another and replace it later, which would - * be a form of "continuation", that even if possible is not - * necessarily a good idea since we sometimes need both an - * unblocked task and its continuation to progress. Instead we - * combine two tactics: - * - * Helping: Arranging for the joiner to execute some task that it - * would be running if the steal had not occurred. Method - * ForkJoinWorkerThread.joinTask tracks joining->stealing - * links to try to find such a task. - * - * Compensating: Unless there are already enough live threads, - * method tryPreBlock() may create or re-activate a spare - * thread to compensate for blocked joiners until they - * unblock. - * - * The ManagedBlocker extension API can't use helping so relies - * only on compensation in method awaitBlocker. - * - * It is impossible to keep exactly the target parallelism number - * of threads running at any given time. Determining the - * existence of conservatively safe helping targets, the - * availability of already-created spares, and the apparent need - * to create new spares are all racy and require heuristic - * guidance, so we rely on multiple retries of each. Currently, - * in keeping with on-demand signalling policy, we compensate only - * if blocking would leave less than one active (non-waiting, - * non-blocked) worker. Additionally, to avoid some false alarms - * due to GC, lagging counters, system activity, etc, compensated - * blocking for joins is only attempted after rechecks stabilize - * (retries are interspersed with Thread.yield, for good - * citizenship). The variable blockedCount, incremented before - * blocking and decremented after, is sometimes needed to - * distinguish cases of waiting for work vs blocking on joins or - * other managed sync. Both cases are equivalent for most pool - * control, so we can update non-atomically. (Additionally, - * contention on blockedCount alleviates some contention on ctl). - * - * Shutdown and Termination. A call to shutdownNow atomically sets - * the ctl stop bit and then (non-atomically) sets each workers - * "terminate" status, cancels all unprocessed tasks, and wakes up - * all waiting workers. Detecting whether termination should - * commence after a non-abrupt shutdown() call requires more work - * and bookkeeping. We need consensus about quiesence (i.e., that - * there is no more work) which is reflected in active counts so - * long as there are no current blockers, as well as possible - * re-evaluations during independent changes in blocking or - * quiescing workers. - * - * Style notes: There is a lot of representation-level coupling - * among classes ForkJoinPool, ForkJoinWorkerThread, and - * ForkJoinTask. Most fields of ForkJoinWorkerThread maintain - * data structures managed by ForkJoinPool, so are directly - * accessed. Conversely we allow access to "workers" array by - * workers, and direct access to ForkJoinTask.status by both - * ForkJoinPool and ForkJoinWorkerThread. There is little point - * trying to reduce this, since any associated future changes in - * representations will need to be accompanied by algorithmic - * changes anyway. All together, these low-level implementation - * choices produce as much as a factor of 4 performance - * improvement compared to naive implementations, and enable the - * processing of billions of tasks per second, at the expense of - * some ugliness. - * - * Methods signalWork() and scan() are the main bottlenecks so are - * especially heavily micro-optimized/mangled. There are lots of - * inline assignments (of form "while ((local = field) != 0)") - * which are usually the simplest way to ensure the required read - * orderings (which are sometimes critical). This leads to a - * "C"-like style of listing declarations of these locals at the - * heads of methods or blocks. There are several occurrences of - * the unusual "do {} while (!cas...)" which is the simplest way - * to force an update of a CAS'ed variable. There are also other - * coding oddities that help some methods perform reasonably even - * when interpreted (not compiled). - * - * The order of declarations in this file is: (1) declarations of - * statics (2) fields (along with constants used when unpacking - * some of them), listed in an order that tends to reduce - * contention among them a bit under most JVMs. (3) internal - * control methods (4) callbacks and other support for - * ForkJoinTask and ForkJoinWorkerThread classes, (5) exported - * methods (plus a few little helpers). (6) static block - * initializing all statics in a minimally dependent order. + * See the extended comments interspersed below for design, + * rationale, and walkthroughs. */ - public static ForkJoinWorkerThread[] copyOfWorkers(ForkJoinWorkerThread[] original, int newLength) { - ForkJoinWorkerThread[] copy = new ForkJoinWorkerThread[newLength]; - System.arraycopy(original, 0, copy, 0, Math.min(newLength, original.length)); - return copy; + /** Mask for packing and unpacking shorts */ + private static final int shortMask = 0xffff; + + /** Max pool size -- must be a power of two minus 1 */ + private static final int MAX_THREADS = 0x7FFF; + + // placeholder for java.util.concurrent.RunnableFuture + interface RunnableFuture<T> extends Runnable { } /** - * Factory for creating new {@link ForkJoinWorkerThread}s. - * A {@code ForkJoinWorkerThreadFactory} must be defined and used - * for {@code ForkJoinWorkerThread} subclasses that extend base - * functionality or initialize threads with different contexts. + * Factory for creating new ForkJoinWorkerThreads. A + * ForkJoinWorkerThreadFactory must be defined and used for + * ForkJoinWorkerThread subclasses that extend base functionality + * or initialize threads with different contexts. */ public static interface ForkJoinWorkerThreadFactory { /** * Returns a new worker thread operating in the given pool. * * @param pool the pool this thread works in - * @throws NullPointerException if the pool is null + * @throws NullPointerException if pool is null; */ public ForkJoinWorkerThread newThread(ForkJoinPool pool); } /** - * Default ForkJoinWorkerThreadFactory implementation; creates a + * Default ForkJoinWorkerThreadFactory implementation, creates a * new ForkJoinWorkerThread. */ - static class DefaultForkJoinWorkerThreadFactory + static class DefaultForkJoinWorkerThreadFactory implements ForkJoinWorkerThreadFactory { public ForkJoinWorkerThread newThread(ForkJoinPool pool) { - return new ForkJoinWorkerThread(pool); + try { + return new ForkJoinWorkerThread(pool); + } catch (OutOfMemoryError oom) { + return null; + } } } @@ -373,13 +110,15 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { * overridden in ForkJoinPool constructors. */ public static final ForkJoinWorkerThreadFactory - defaultForkJoinWorkerThreadFactory; + defaultForkJoinWorkerThreadFactory = + new DefaultForkJoinWorkerThreadFactory(); /** * Permission required for callers of methods that may start or * kill threads. */ - private static final RuntimePermission modifyThreadPermission; + private static final RuntimePermission modifyThreadPermission = + new RuntimePermission("modifyThread"); /** * If there is a security manager, makes sure caller has @@ -394,59 +133,33 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { /** * Generator for assigning sequence numbers as pool names. */ - private static final AtomicInteger poolNumberGenerator; - - /** - * Generator for initial random seeds for worker victim - * selection. This is used only to create initial seeds. Random - * steals use a cheaper xorshift generator per steal attempt. We - * don't expect much contention on seedGenerator, so just use a - * plain Random. - */ - static final Random workerSeedGenerator; + private static final AtomicInteger poolNumberGenerator = + new AtomicInteger(); /** - * Array holding all worker threads in the pool. Initialized upon - * construction. Array size must be a power of two. Updates and - * replacements are protected by scanGuard, but the array is - * always kept in a consistent enough state to be randomly - * accessed without locking by workers performing work-stealing, - * as well as other traversal-based methods in this class, so long - * as reads memory-acquire by first reading ctl. All readers must - * tolerate that some array slots may be null. + * Array holding all worker threads in the pool. Initialized upon + * first use. Array size must be a power of two. Updates and + * replacements are protected by workerLock, but it is always kept + * in a consistent enough state to be randomly accessed without + * locking by workers performing work-stealing. */ - ForkJoinWorkerThread[] workers; + public volatile ForkJoinWorkerThread[] workers; /** - * Initial size for submission queue array. Must be a power of - * two. In many applications, these always stay small so we use a - * small initial cap. + * Lock protecting access to workers. */ - private static final int INITIAL_QUEUE_CAPACITY = 8; + private final ReentrantLock workerLock; /** - * Maximum size for submission queue array. Must be a power of two - * less than or equal to 1 << (31 - width of array entry) to - * ensure lack of index wraparound, but is capped at a lower - * value to help users trap runaway computations. + * Condition for awaitTermination. */ - private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M - - /** - * Array serving as submission queue. Initialized upon construction. - */ - private ForkJoinTask<?>[] submissionQueue; - - /** - * Lock protecting submissions array for addSubmission - */ - private final ReentrantLock submissionLock; + private final Condition termination; /** - * Condition for awaitTermination, using submissionLock for - * convenience. + * The uncaught exception handler used when any worker + * abrupty terminates */ - private final Condition termination; + private Thread.UncaughtExceptionHandler ueh; /** * Creation factory for worker threads. @@ -454,1229 +167,692 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { private final ForkJoinWorkerThreadFactory factory; /** - * The uncaught exception handler used when any worker abruptly - * terminates. - */ - final Thread.UncaughtExceptionHandler ueh; - - /** - * Prefix for assigning names to worker threads + * Head of stack of threads that were created to maintain + * parallelism when other threads blocked, but have since + * suspended when the parallelism level rose. */ - private final String workerNamePrefix; + private volatile WaitQueueNode spareStack; /** * Sum of per-thread steal counts, updated only when threads are * idle or terminating. */ - private volatile long stealCount; + private final AtomicLong stealCount; /** - * Main pool control -- a long packed with: - * AC: Number of active running workers minus target parallelism (16 bits) - * TC: Number of total workers minus target parallelism (16bits) - * ST: true if pool is terminating (1 bit) - * EC: the wait count of top waiting thread (15 bits) - * ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits) - * - * When convenient, we can extract the upper 32 bits of counts and - * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e = - * (int)ctl. The ec field is never accessed alone, but always - * together with id and st. The offsets of counts by the target - * parallelism and the positionings of fields makes it possible to - * perform the most common checks via sign tests of fields: When - * ac is negative, there are not enough active workers, when tc is - * negative, there are not enough total workers, when id is - * negative, there is at least one waiting worker, and when e is - * negative, the pool is terminating. To deal with these possibly - * negative fields, we use casts in and out of "short" and/or - * signed shifts to maintain signedness. + * Queue for external submissions. */ - volatile long ctl; - - // bit positions/shifts for fields - private static final int AC_SHIFT = 48; - private static final int TC_SHIFT = 32; - private static final int ST_SHIFT = 31; - private static final int EC_SHIFT = 16; - - // bounds - private static final int MAX_ID = 0x7fff; // max poolIndex - private static final int SMASK = 0xffff; // mask short bits - private static final int SHORT_SIGN = 1 << 15; - private static final int INT_SIGN = 1 << 31; - - // masks - private static final long STOP_BIT = 0x0001L << ST_SHIFT; - private static final long AC_MASK = ((long)SMASK) << AC_SHIFT; - private static final long TC_MASK = ((long)SMASK) << TC_SHIFT; - - // units for incrementing and decrementing - private static final long TC_UNIT = 1L << TC_SHIFT; - private static final long AC_UNIT = 1L << AC_SHIFT; - - // masks and units for dealing with u = (int)(ctl >>> 32) - private static final int UAC_SHIFT = AC_SHIFT - 32; - private static final int UTC_SHIFT = TC_SHIFT - 32; - private static final int UAC_MASK = SMASK << UAC_SHIFT; - private static final int UTC_MASK = SMASK << UTC_SHIFT; - private static final int UAC_UNIT = 1 << UAC_SHIFT; - private static final int UTC_UNIT = 1 << UTC_SHIFT; - - // masks and units for dealing with e = (int)ctl - private static final int E_MASK = 0x7fffffff; // no STOP_BIT - private static final int EC_UNIT = 1 << EC_SHIFT; + private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; /** - * The target parallelism level. + * Head of Treiber stack for barrier sync. See below for explanation */ - final int parallelism; + private volatile WaitQueueNode syncStack; /** - * Index (mod submission queue length) of next element to take - * from submission queue. Usage is identical to that for - * per-worker queues -- see ForkJoinWorkerThread internal - * documentation. + * The count for event barrier */ - volatile int queueBase; + private volatile long eventCount; /** - * Index (mod submission queue length) of next element to add - * in submission queue. Usage is identical to that for - * per-worker queues -- see ForkJoinWorkerThread internal - * documentation. + * Pool number, just for assigning useful names to worker threads */ - int queueTop; + private final int poolNumber; /** - * True when shutdown() has been called. + * The maximum allowed pool size */ - volatile boolean shutdown; + private volatile int maxPoolSize; /** - * True if use local fifo, not default lifo, for local polling - * Read by, and replicated by ForkJoinWorkerThreads + * The desired parallelism level, updated only under workerLock. */ - final boolean locallyFifo; + private volatile int parallelism; /** - * The number of threads in ForkJoinWorkerThreads.helpQuiescePool. - * When non-zero, suppresses automatic shutdown when active - * counts become zero. + * True if use local fifo, not default lifo, for local polling */ - volatile int quiescerCount; + private volatile boolean locallyFifo; /** - * The number of threads blocked in join. + * Holds number of total (i.e., created and not yet terminated) + * and running (i.e., not blocked on joins or other managed sync) + * threads, packed into one int to ensure consistent snapshot when + * making decisions about creating and suspending spare + * threads. Updated only by CAS. Note: CASes in + * updateRunningCount and preJoin running active count is in low + * word, so need to be modified if this changes */ - volatile int blockedCount; + private volatile int workerCounts; + + private static int totalCountOf(int s) { return s >>> 16; } + private static int runningCountOf(int s) { return s & shortMask; } + private static int workerCountsFor(int t, int r) { return (t << 16) + r; } /** - * Counter for worker Thread names (unrelated to their poolIndex) + * Add delta (which may be negative) to running count. This must + * be called before (with negative arg) and after (with positive) + * any managed synchronization (i.e., mainly, joins) + * @param delta the number to add */ - private volatile int nextWorkerNumber; + final void updateRunningCount(int delta) { + int s; + do;while (!casWorkerCounts(s = workerCounts, s + delta)); + } /** - * The index for the next created worker. Accessed under scanGuard. + * Add delta (which may be negative) to both total and running + * count. This must be called upon creation and termination of + * worker threads. + * @param delta the number to add */ - private int nextWorkerIndex; + private void updateWorkerCount(int delta) { + int d = delta + (delta << 16); // add to both lo and hi parts + int s; + do;while (!casWorkerCounts(s = workerCounts, s + d)); + } /** - * SeqLock and index masking for updates to workers array. Locked - * when SG_UNIT is set. Unlocking clears bit by adding - * SG_UNIT. Staleness of read-only operations can be checked by - * comparing scanGuard to value before the reads. The low 16 bits - * (i.e, anding with SMASK) hold (the smallest power of two - * covering all worker indices, minus one, and is used to avoid - * dealing with large numbers of null slots when the workers array - * is overallocated. + * Lifecycle control. High word contains runState, low word + * contains the number of workers that are (probably) executing + * tasks. This value is atomically incremented before a worker + * gets a task to run, and decremented when worker has no tasks + * and cannot find any. These two fields are bundled together to + * support correct termination triggering. Note: activeCount + * CAS'es cheat by assuming active count is in low word, so need + * to be modified if this changes */ - volatile int scanGuard; + private volatile int runControl; + + // RunState values. Order among values matters + private static final int RUNNING = 0; + private static final int SHUTDOWN = 1; + private static final int TERMINATING = 2; + private static final int TERMINATED = 3; - private static final int SG_UNIT = 1 << 16; + private static int runStateOf(int c) { return c >>> 16; } + private static int activeCountOf(int c) { return c & shortMask; } + private static int runControlFor(int r, int a) { return (r << 16) + a; } /** - * The wakeup interval (in nanoseconds) for a worker waiting for a - * task when the pool is quiescent to instead try to shrink the - * number of workers. The exact value does not matter too - * much. It must be short enough to release resources during - * sustained periods of idleness, but not so short that threads - * are continually re-created. + * Try incrementing active count; fail on contention. Called by + * workers before/during executing tasks. + * @return true on success; */ - private static final long SHRINK_RATE = - 4L * 1000L * 1000L * 1000L; // 4 seconds + final boolean tryIncrementActiveCount() { + int c = runControl; + return casRunControl(c, c+1); + } /** - * Top-level loop for worker threads: On each step: if the - * previous step swept through all queues and found no tasks, or - * there are excess threads, then possibly blocks. Otherwise, - * scans for and, if found, executes a task. Returns when pool - * and/or worker terminate. - * - * @param w the worker + * Try decrementing active count; fail on contention. + * Possibly trigger termination on success + * Called by workers when they can't find tasks. + * @return true on success */ - final void work(ForkJoinWorkerThread w) { - boolean swept = false; // true on empty scans - long c; - while (!w.terminate && (int)(c = ctl) >= 0) { - int a; // active count - if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0) - swept = scan(w, a); - else if (tryAwaitWork(w, c)) - swept = false; - } + final boolean tryDecrementActiveCount() { + int c = runControl; + int nextc = c - 1; + if (!casRunControl(c, nextc)) + return false; + if (canTerminateOnShutdown(nextc)) + terminateOnShutdown(); + return true; } - // Signalling - /** - * Wakes up or creates a worker. + * Return true if argument represents zero active count and + * nonzero runstate, which is the triggering condition for + * terminating on shutdown. */ - final void signalWork() { - /* - * The while condition is true if: (there is are too few total - * workers OR there is at least one waiter) AND (there are too - * few active workers OR the pool is terminating). The value - * of e distinguishes the remaining cases: zero (no waiters) - * for create, negative if terminating (in which case do - * nothing), else release a waiter. The secondary checks for - * release (non-null array etc) can fail if the pool begins - * terminating after the test, and don't impose any added cost - * because JVMs must perform null and bounds checks anyway. - */ - long c; int e, u; - while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) & - (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) { - if (e > 0) { // release a waiting worker - int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; - if ((ws = workers) == null || - (i = ~e & SMASK) >= ws.length || - (w = ws[i]) == null) - break; - long nc = (((long)(w.nextWait & E_MASK)) | - ((long)(u + UAC_UNIT) << 32)); - if (w.eventCount == e && - UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { - w.eventCount = (e + EC_UNIT) & E_MASK; - if (w.parked) - UNSAFE.unpark(w); - break; - } - } - else if (UNSAFE.compareAndSwapLong - (this, ctlOffset, c, - (long)(((u + UTC_UNIT) & UTC_MASK) | - ((u + UAC_UNIT) & UAC_MASK)) << 32)) { - addWorker(); - break; - } - } + private static boolean canTerminateOnShutdown(int c) { + return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit } /** - * Variant of signalWork to help release waiters on rescans. - * Tries once to release a waiter if active count < 0. - * - * @return false if failed due to contention, else true - */ - private boolean tryReleaseWaiter() { - long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; - if ((e = (int)(c = ctl)) > 0 && - (int)(c >> AC_SHIFT) < 0 && - (ws = workers) != null && - (i = ~e & SMASK) < ws.length && - (w = ws[i]) != null) { - long nc = ((long)(w.nextWait & E_MASK) | - ((c + AC_UNIT) & (AC_MASK|TC_MASK))); - if (w.eventCount != e || - !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) + * Transition run state to at least the given state. Return true + * if not already at least given state. + */ + private boolean transitionRunStateTo(int state) { + for (;;) { + int c = runControl; + if (runStateOf(c) >= state) return false; - w.eventCount = (e + EC_UNIT) & E_MASK; - if (w.parked) - UNSAFE.unpark(w); + if (casRunControl(c, runControlFor(state, activeCountOf(c)))) + return true; } - return true; } - // Scanning for tasks + /** + * Controls whether to add spares to maintain parallelism + */ + private volatile boolean maintainsParallelism; + + // Constructors /** - * Scans for and, if found, executes one task. Scans start at a - * random index of workers array, and randomly select the first - * (2*#workers)-1 probes, and then, if all empty, resort to 2 - * circular sweeps, which is necessary to check quiescence. and - * taking a submission only if no stealable tasks were found. The - * steal code inside the loop is a specialized form of - * ForkJoinWorkerThread.deqTask, followed bookkeeping to support - * helpJoinTask and signal propagation. The code for submission - * queues is almost identical. On each steal, the worker completes - * not only the task, but also all local tasks that this task may - * have generated. On detecting staleness or contention when - * trying to take a task, this method returns without finishing - * sweep, which allows global state rechecks before retry. - * - * @param w the worker - * @param a the number of active workers - * @return true if swept all queues without finding a task + * Creates a ForkJoinPool with a pool size equal to the number of + * processors available on the system and using the default + * ForkJoinWorkerThreadFactory, + * @throws SecurityException if a security manager exists and + * the caller is not permitted to modify threads + * because it does not hold {@link + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ - private boolean scan(ForkJoinWorkerThread w, int a) { - int g = scanGuard; // mask 0 avoids useless scans if only one active - int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK; - ForkJoinWorkerThread[] ws = workers; - if (ws == null || ws.length <= m) // staleness check - return false; - for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) { - ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; - ForkJoinWorkerThread v = ws[k & m]; - if (v != null && (b = v.queueBase) != v.queueTop && - (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) { - long u = (i << ASHIFT) + ABASE; - if ((t = q[i]) != null && v.queueBase == b && - UNSAFE.compareAndSwapObject(q, u, t, null)) { - int d = (v.queueBase = b + 1) - v.queueTop; - v.stealHint = w.poolIndex; - if (d != 0) - signalWork(); // propagate if nonempty - w.execTask(t); - } - r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5); - return false; // store next seed - } - else if (j < 0) { // xorshift - r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5; - } - else - ++k; - } - if (scanGuard != g) // staleness check - return false; - else { // try to take submission - ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; - if ((b = queueBase) != queueTop && - (q = submissionQueue) != null && - (i = (q.length - 1) & b) >= 0) { - long u = (i << ASHIFT) + ABASE; - if ((t = q[i]) != null && queueBase == b && - UNSAFE.compareAndSwapObject(q, u, t, null)) { - queueBase = b + 1; - w.execTask(t); - } - return false; - } - return true; // all queues empty - } + public ForkJoinPool() { + this(Runtime.getRuntime().availableProcessors(), + defaultForkJoinWorkerThreadFactory); } /** - * Tries to enqueue worker w in wait queue and await change in - * worker's eventCount. If the pool is quiescent and there is - * more than one worker, possibly terminates worker upon exit. - * Otherwise, before blocking, rescans queues to avoid missed - * signals. Upon finding work, releases at least one worker - * (which may be the current worker). Rescans restart upon - * detected staleness or failure to release due to - * contention. Note the unusual conventions about Thread.interrupt - * here and elsewhere: Because interrupts are used solely to alert - * threads to check termination, which is checked here anyway, we - * clear status (using Thread.interrupted) before any call to - * park, so that park does not immediately return due to status - * being set via some other unrelated call to interrupt in user - * code. - * - * @param w the calling worker - * @param c the ctl value on entry - * @return true if waited or another thread was released upon enq - */ - private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) { - int v = w.eventCount; - w.nextWait = (int)c; // w's successor record - long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK)); - if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { - long d = ctl; // return true if lost to a deq, to force scan - return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L; - } - for (int sc = w.stealCount; sc != 0;) { // accumulate stealCount - long s = stealCount; - if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc)) - sc = w.stealCount = 0; - else if (w.eventCount != v) - return true; // update next time - } - if ((!shutdown || !tryTerminate(false)) && - (int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 && - blockedCount == 0 && quiescerCount == 0) - idleAwaitWork(w, nc, c, v); // quiescent - for (boolean rescanned = false;;) { - if (w.eventCount != v) - return true; - if (!rescanned) { - int g = scanGuard, m = g & SMASK; - ForkJoinWorkerThread[] ws = workers; - if (ws != null && m < ws.length) { - rescanned = true; - for (int i = 0; i <= m; ++i) { - ForkJoinWorkerThread u = ws[i]; - if (u != null) { - if (u.queueBase != u.queueTop && - !tryReleaseWaiter()) - rescanned = false; // contended - if (w.eventCount != v) - return true; - } - } - } - if (scanGuard != g || // stale - (queueBase != queueTop && !tryReleaseWaiter())) - rescanned = false; - if (!rescanned) - Thread.yield(); // reduce contention - else - Thread.interrupted(); // clear before park - } - else { - w.parked = true; // must recheck - if (w.eventCount != v) { - w.parked = false; - return true; - } - LockSupport.park(this); - rescanned = w.parked = false; - } - } + * Creates a ForkJoinPool with the indicated parellelism level + * threads, and using the default ForkJoinWorkerThreadFactory, + * @param parallelism the number of worker threads + * @throws IllegalArgumentException if parallelism less than or + * equal to zero + * @throws SecurityException if a security manager exists and + * the caller is not permitted to modify threads + * because it does not hold {@link + * java.lang.RuntimePermission}<code>("modifyThread")</code>, + */ + public ForkJoinPool(int parallelism) { + this(parallelism, defaultForkJoinWorkerThreadFactory); } /** - * If inactivating worker w has caused pool to become - * quiescent, check for pool termination, and wait for event - * for up to SHRINK_RATE nanosecs (rescans are unnecessary in - * this case because quiescence reflects consensus about lack - * of work). On timeout, if ctl has not changed, terminate the - * worker. Upon its termination (see deregisterWorker), it may - * wake up another worker to possibly repeat this process. - * - * @param w the calling worker - * @param currentCtl the ctl value after enqueuing w - * @param prevCtl the ctl value if w terminated - * @param v the eventCount w awaits change - */ - private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl, - long prevCtl, int v) { - if (w.eventCount == v) { - if (shutdown) - tryTerminate(false); - ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs - while (ctl == currentCtl) { - long startTime = System.nanoTime(); - w.parked = true; - if (w.eventCount == v) // must recheck - LockSupport.parkNanos(this, SHRINK_RATE); - w.parked = false; - if (w.eventCount != v) - break; - else if (System.nanoTime() - startTime < - SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop - Thread.interrupted(); // spurious wakeup - else if (UNSAFE.compareAndSwapLong(this, ctlOffset, - currentCtl, prevCtl)) { - w.terminate = true; // restore previous - w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK; - break; - } - } - } + * Creates a ForkJoinPool with parallelism equal to the number of + * processors available on the system and using the given + * ForkJoinWorkerThreadFactory, + * @param factory the factory for creating new threads + * @throws NullPointerException if factory is null + * @throws SecurityException if a security manager exists and + * the caller is not permitted to modify threads + * because it does not hold {@link + * java.lang.RuntimePermission}<code>("modifyThread")</code>, + */ + public ForkJoinPool(ForkJoinWorkerThreadFactory factory) { + this(Runtime.getRuntime().availableProcessors(), factory); } - // Submissions - /** - * Enqueues the given task in the submissionQueue. Same idea as - * ForkJoinWorkerThread.pushTask except for use of submissionLock. + * Creates a ForkJoinPool with the given parallelism and factory. * - * @param t the task + * @param parallelism the targeted number of worker threads + * @param factory the factory for creating new threads + * @throws IllegalArgumentException if parallelism less than or + * equal to zero, or greater than implementation limit. + * @throws NullPointerException if factory is null + * @throws SecurityException if a security manager exists and + * the caller is not permitted to modify threads + * because it does not hold {@link + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ - private void addSubmission(ForkJoinTask<?> t) { - final ReentrantLock lock = this.submissionLock; - lock.lock(); - try { - ForkJoinTask<?>[] q; int s, m; - if ((q = submissionQueue) != null) { // ignore if queue removed - long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE; - UNSAFE.putOrderedObject(q, u, t); - queueTop = s + 1; - if (s - queueBase == m) - growSubmissionQueue(); - } - } finally { - lock.unlock(); - } - signalWork(); - } - - // (pollSubmission is defined below with exported methods) - - /** - * Creates or doubles submissionQueue array. - * Basically identical to ForkJoinWorkerThread version. - */ - private void growSubmissionQueue() { - ForkJoinTask<?>[] oldQ = submissionQueue; - int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY; - if (size > MAXIMUM_QUEUE_CAPACITY) - throw new RejectedExecutionException("Queue capacity exceeded"); - if (size < INITIAL_QUEUE_CAPACITY) - size = INITIAL_QUEUE_CAPACITY; - ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size]; - int mask = size - 1; - int top = queueTop; - int oldMask; - if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) { - for (int b = queueBase; b != top; ++b) { - long u = ((b & oldMask) << ASHIFT) + ABASE; - Object x = UNSAFE.getObjectVolatile(oldQ, u); - if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null)) - UNSAFE.putObjectVolatile - (q, ((b & mask) << ASHIFT) + ABASE, x); - } + public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) { + if (parallelism <= 0 || parallelism > MAX_THREADS) + throw new IllegalArgumentException(); + if (factory == null) + throw new NullPointerException(); + checkPermission(); + this.factory = factory; + this.parallelism = parallelism; + this.maxPoolSize = MAX_THREADS; + this.maintainsParallelism = true; + this.poolNumber = poolNumberGenerator.incrementAndGet(); + this.workerLock = new ReentrantLock(); + this.termination = workerLock.newCondition(); + this.stealCount = new AtomicLong(); + this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); + // worker array and workers are lazily constructed + } + + /** + * Create new worker using factory. + * @param index the index to assign worker + * @return new worker, or null of factory failed + */ + private ForkJoinWorkerThread createWorker(int index) { + Thread.UncaughtExceptionHandler h = ueh; + ForkJoinWorkerThread w = factory.newThread(this); + if (w != null) { + w.poolIndex = index; + w.setDaemon(true); + w.setAsyncMode(locallyFifo); + w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index); + if (h != null) + w.setUncaughtExceptionHandler(h); } + return w; } - // Blocking support - /** - * Tries to increment blockedCount, decrement active count - * (sometimes implicitly) and possibly release or create a - * compensating worker in preparation for blocking. Fails - * on contention or termination. - * - * @return true if the caller can block, else should recheck and retry - */ - private boolean tryPreBlock() { - int b = blockedCount; - if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) { - int pc = parallelism; - do { - ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w; - int e, ac, tc, rc, i; - long c = ctl; - int u = (int)(c >>> 32); - if ((e = (int)c) < 0) { - // skip -- terminating - } - else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 && - (ws = workers) != null && - (i = ~e & SMASK) < ws.length && - (w = ws[i]) != null) { - long nc = ((long)(w.nextWait & E_MASK) | - (c & (AC_MASK|TC_MASK))); - if (w.eventCount == e && - UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { - w.eventCount = (e + EC_UNIT) & E_MASK; - if (w.parked) - UNSAFE.unpark(w); - return true; // release an idle worker - } - } - else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) { - long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK); - if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) - return true; // no compensation needed - } - else if (tc + pc < MAX_ID) { - long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); - if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { - addWorker(); - return true; // create a replacement - } - } - // try to back out on any failure and let caller retry - } while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset, - b = blockedCount, b - 1)); - } - return false; + * Return a good size for worker array given pool size. + * Currently requires size to be a power of two. + */ + private static int arraySizeFor(int ps) { + return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1))); + } + + public static ForkJoinWorkerThread[] copyOfWorkers(ForkJoinWorkerThread[] original, int newLength) { + ForkJoinWorkerThread[] copy = new ForkJoinWorkerThread[newLength]; + System.arraycopy(original, 0, copy, 0, Math.min(newLength, original.length)); + return copy; } /** - * Decrements blockedCount and increments active count + * Create or resize array if necessary to hold newLength. + * Call only under exlusion or lock + * @return the array */ - private void postBlock() { - long c; - do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, // no mask - c = ctl, c + AC_UNIT)); - int b; - do {} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset, - b = blockedCount, b - 1)); + private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) { + ForkJoinWorkerThread[] ws = workers; + if (ws == null) + return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)]; + else if (newLength > ws.length) + return workers = copyOfWorkers(ws, arraySizeFor(newLength)); + else + return ws; } /** - * Possibly blocks waiting for the given task to complete, or - * cancels the task if terminating. Fails to wait if contended. - * - * @param joinMe the task + * Try to shrink workers into smaller array after one or more terminate */ - final void tryAwaitJoin(ForkJoinTask<?> joinMe) { - int s; - Thread.interrupted(); // clear interrupts before checking termination - if (joinMe.status >= 0) { - if (tryPreBlock()) { - joinMe.tryAwaitDone(0L); - postBlock(); - } - else if ((ctl & STOP_BIT) != 0L) - joinMe.cancelIgnoringExceptions(); + private void tryShrinkWorkerArray() { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + int len = ws.length; + int last = len - 1; + while (last >= 0 && ws[last] == null) + --last; + int newLength = arraySizeFor(last+1); + if (newLength < len) + workers = copyOfWorkers(ws, newLength); } } /** - * Possibly blocks the given worker waiting for joinMe to - * complete or timeout - * - * @param joinMe the task - * @param millis the wait time for underlying Object.wait - */ - final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) { - while (joinMe.status >= 0) { - Thread.interrupted(); - if ((ctl & STOP_BIT) != 0L) { - joinMe.cancelIgnoringExceptions(); - break; - } - if (tryPreBlock()) { - long last = System.nanoTime(); - while (joinMe.status >= 0) { - long millis = TimeUnit.NANOSECONDS.toMillis(nanos); - if (millis <= 0) - break; - joinMe.tryAwaitDone(millis); - if (joinMe.status < 0) - break; - if ((ctl & STOP_BIT) != 0L) { - joinMe.cancelIgnoringExceptions(); - break; + * Initialize workers if necessary + */ + final void ensureWorkerInitialization() { + ForkJoinWorkerThread[] ws = workers; + if (ws == null) { + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + ws = workers; + if (ws == null) { + int ps = parallelism; + ws = ensureWorkerArrayCapacity(ps); + for (int i = 0; i < ps; ++i) { + ForkJoinWorkerThread w = createWorker(i); + if (w != null) { + ws[i] = w; + w.start(); + updateWorkerCount(1); + } } - long now = System.nanoTime(); - nanos -= now - last; - last = now; } - postBlock(); - break; + } finally { + lock.unlock(); } } } /** - * If necessary, compensates for blocker, and blocks + * Worker creation and startup for threads added via setParallelism. */ - private void awaitBlocker(ManagedBlocker blocker) - throws InterruptedException { - while (!blocker.isReleasable()) { - if (tryPreBlock()) { - try { - do {} while (!blocker.isReleasable() && !blocker.block()); - } finally { - postBlock(); - } + private void createAndStartAddedWorkers() { + resumeAllSpares(); // Allow spares to convert to nonspare + int ps = parallelism; + ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps); + int len = ws.length; + // Sweep through slots, to keep lowest indices most populated + int k = 0; + while (k < len) { + if (ws[k] != null) { + ++k; + continue; + } + int s = workerCounts; + int tc = totalCountOf(s); + int rc = runningCountOf(s); + if (rc >= ps || tc >= ps) break; + if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) { + ForkJoinWorkerThread w = createWorker(k); + if (w != null) { + ws[k++] = w; + w.start(); + } + else { + updateWorkerCount(-1); // back out on failed creation + break; + } } } } - // Creating, registering and deregistring workers + // Execution methods /** - * Tries to create and start a worker; minimally rolls back counts - * on failure. + * Common code for execute, invoke and submit */ - private void addWorker() { - Throwable ex = null; - ForkJoinWorkerThread t = null; - try { - t = factory.newThread(this); - } catch (Throwable e) { - ex = e; - } - if (t == null) { // null or exceptional factory return - long c; // adjust counts - do {} while (!UNSAFE.compareAndSwapLong - (this, ctlOffset, c = ctl, - (((c - AC_UNIT) & AC_MASK) | - ((c - TC_UNIT) & TC_MASK) | - (c & ~(AC_MASK|TC_MASK))))); - // Propagate exception if originating from an external caller - if (!tryTerminate(false) && ex != null && - !(Thread.currentThread() instanceof ForkJoinWorkerThread)) - UNSAFE.throwException(ex); - } - else - t.start(); + private <T> void doSubmit(ForkJoinTask<T> task) { + if (isShutdown()) + throw new RejectedExecutionException(); + if (workers == null) + ensureWorkerInitialization(); + submissionQueue.offer(task); + signalIdleWorkers(); } /** - * Callback from ForkJoinWorkerThread constructor to assign a - * public name + * Performs the given task; returning its result upon completion + * @param task the task + * @return the task's result + * @throws NullPointerException if task is null + * @throws RejectedExecutionException if pool is shut down */ - final String nextWorkerName() { - for (int n;;) { - if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset, - n = nextWorkerNumber, ++n)) - return workerNamePrefix + n; - } + public <T> T invoke(ForkJoinTask<T> task) { + doSubmit(task); + return task.join(); } /** - * Callback from ForkJoinWorkerThread constructor to - * determine its poolIndex and record in workers array. - * - * @param w the worker - * @return the worker's pool index - */ - final int registerWorker(ForkJoinWorkerThread w) { - /* - * In the typical case, a new worker acquires the lock, uses - * next available index and returns quickly. Since we should - * not block callers (ultimately from signalWork or - * tryPreBlock) waiting for the lock needed to do this, we - * instead help release other workers while waiting for the - * lock. - */ - for (int g;;) { - ForkJoinWorkerThread[] ws; - if (((g = scanGuard) & SG_UNIT) == 0 && - UNSAFE.compareAndSwapInt(this, scanGuardOffset, - g, g | SG_UNIT)) { - int k = nextWorkerIndex; - try { - if ((ws = workers) != null) { // ignore on shutdown - int n = ws.length; - if (k < 0 || k >= n || ws[k] != null) { - for (k = 0; k < n && ws[k] != null; ++k) - ; - if (k == n) - ws = workers = Arrays.copyOf(ws, n << 1); - } - ws[k] = w; - nextWorkerIndex = k + 1; - int m = g & SMASK; - g = (k > m) ? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1); - } - } finally { - scanGuard = g; - } - return k; - } - else if ((ws = workers) != null) { // help release others - for (ForkJoinWorkerThread u : ws) { - if (u != null && u.queueBase != u.queueTop) { - if (tryReleaseWaiter()) - break; - } - } - } - } + * Arranges for (asynchronous) execution of the given task. + * @param task the task + * @throws NullPointerException if task is null + * @throws RejectedExecutionException if pool is shut down + */ + public <T> void execute(ForkJoinTask<T> task) { + doSubmit(task); } - /** - * Final callback from terminating worker. Removes record of - * worker from array, and adjusts counts. If pool is shutting - * down, tries to complete termination. - * - * @param w the worker - */ - final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) { - int idx = w.poolIndex; - int sc = w.stealCount; - int steps = 0; - // Remove from array, adjust worker counts and collect steal count. - // We can intermix failed removes or adjusts with steal updates - do { - long s, c; - int g; - if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 && - UNSAFE.compareAndSwapInt(this, scanGuardOffset, - g, g |= SG_UNIT)) { - ForkJoinWorkerThread[] ws = workers; - if (ws != null && idx >= 0 && - idx < ws.length && ws[idx] == w) - ws[idx] = null; // verify - nextWorkerIndex = idx; - scanGuard = g + SG_UNIT; - steps = 1; - } - if (steps == 1 && - UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl, - (((c - AC_UNIT) & AC_MASK) | - ((c - TC_UNIT) & TC_MASK) | - (c & ~(AC_MASK|TC_MASK))))) - steps = 2; - if (sc != 0 && - UNSAFE.compareAndSwapLong(this, stealCountOffset, - s = stealCount, s + sc)) - sc = 0; - } while (steps != 2 || sc != 0); - if (!tryTerminate(false)) { - if (ex != null) // possibly replace if died abnormally - signalWork(); - else - tryReleaseWaiter(); - } + // AbstractExecutorService methods + + public void execute(Runnable task) { + doSubmit(new AdaptedRunnable<Void>(task, null)); } - // Shutdown and termination + public <T> ForkJoinTask<T> submit(Callable<T> task) { + ForkJoinTask<T> job = new AdaptedCallable<T>(task); + doSubmit(job); + return job; + } - /** - * Possibly initiates and/or completes termination. - * - * @param now if true, unconditionally terminate, else only - * if shutdown and empty queue and no active workers - * @return true if now terminating or terminated - */ - private boolean tryTerminate(boolean now) { - long c; - while (((c = ctl) & STOP_BIT) == 0) { - if (!now) { - if ((int)(c >> AC_SHIFT) != -parallelism) - return false; - if (!shutdown || blockedCount != 0 || quiescerCount != 0 || - queueBase != queueTop) { - if (ctl == c) // staleness check - return false; - continue; - } - } - if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT)) - startTerminating(); - } - if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers - final ReentrantLock lock = this.submissionLock; - lock.lock(); - try { - termination.signalAll(); - } finally { - lock.unlock(); - } - } - return true; + public <T> ForkJoinTask<T> submit(Runnable task, T result) { + ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result); + doSubmit(job); + return job; } - /** - * Runs up to three passes through workers: (0) Setting - * termination status for each worker, followed by wakeups up to - * queued workers; (1) helping cancel tasks; (2) interrupting - * lagging threads (likely in external tasks, but possibly also - * blocked in joins). Each pass repeats previous steps because of - * potential lagging thread creation. - */ - private void startTerminating() { - cancelSubmissions(); - for (int pass = 0; pass < 3; ++pass) { - ForkJoinWorkerThread[] ws = workers; - if (ws != null) { - for (ForkJoinWorkerThread w : ws) { - if (w != null) { - w.terminate = true; - if (pass > 0) { - w.cancelTasks(); - if (pass > 1 && !w.isInterrupted()) { - try { - w.interrupt(); - } catch (SecurityException ignore) { - } - } - } - } - } - terminateWaiters(); - } - } + public ForkJoinTask<?> submit(Runnable task) { + ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null); + doSubmit(job); + return job; } /** - * Polls and cancels all submissions. Called only during termination. + * Adaptor for Runnables. This implements RunnableFuture + * to be compliant with AbstractExecutorService constraints */ - private void cancelSubmissions() { - while (queueBase != queueTop) { - ForkJoinTask<?> task = pollSubmission(); - if (task != null) { - try { - task.cancel(false); - } catch (Throwable ignore) { - } - } + static final class AdaptedRunnable<T> extends ForkJoinTask<T> + implements RunnableFuture<T> { + final Runnable runnable; + final T resultOnCompletion; + T result; + AdaptedRunnable(Runnable runnable, T result) { + if (runnable == null) throw new NullPointerException(); + this.runnable = runnable; + this.resultOnCompletion = result; } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + runnable.run(); + result = resultOnCompletion; + return true; + } + public void run() { invoke(); } } /** - * Tries to set the termination status of waiting workers, and - * then wakes them up (after which they will terminate). + * Adaptor for Callables */ - private void terminateWaiters() { - ForkJoinWorkerThread[] ws = workers; - if (ws != null) { - ForkJoinWorkerThread w; long c; int i, e; - int n = ws.length; - while ((i = ~(e = (int)(c = ctl)) & SMASK) < n && - (w = ws[i]) != null && w.eventCount == (e & E_MASK)) { - if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, - (long)(w.nextWait & E_MASK) | - ((c + AC_UNIT) & AC_MASK) | - (c & (TC_MASK|STOP_BIT)))) { - w.terminate = true; - w.eventCount = e + EC_UNIT; - if (w.parked) - UNSAFE.unpark(w); - } + static final class AdaptedCallable<T> extends ForkJoinTask<T> + implements RunnableFuture<T> { + final Callable<T> callable; + T result; + AdaptedCallable(Callable<T> callable) { + if (callable == null) throw new NullPointerException(); + this.callable = callable; + } + public T getRawResult() { return result; } + public void setRawResult(T v) { result = v; } + public boolean exec() { + try { + result = callable.call(); + return true; + } catch (Error err) { + throw err; + } catch (RuntimeException rex) { + throw rex; + } catch (Exception ex) { + throw new RuntimeException(ex); } } + public void run() { invoke(); } } - // misc ForkJoinWorkerThread support + public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { + ArrayList<ForkJoinTask<T>> ts = + new ArrayList<ForkJoinTask<T>>(tasks.size()); + for (Callable<T> c : tasks) + ts.add(new AdaptedCallable<T>(c)); + invoke(new InvokeAll<T>(ts)); + return (List<Future<T>>)(List)ts; + } - /** - * Increment or decrement quiescerCount. Needed only to prevent - * triggering shutdown if a worker is transiently inactive while - * checking quiescence. - * - * @param delta 1 for increment, -1 for decrement - */ - final void addQuiescerCount(int delta) { - int c; - do {} while (!UNSAFE.compareAndSwapInt(this, quiescerCountOffset, - c = quiescerCount, c + delta)); + static final class InvokeAll<T> extends RecursiveAction { + final ArrayList<ForkJoinTask<T>> tasks; + InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } + public void compute() { + try { invokeAll(tasks); } catch(Exception ignore) {} + } } + // Configuration and status settings and queries + /** - * Directly increment or decrement active count without - * queuing. This method is used to transiently assert inactivation - * while checking quiescence. + * Returns the factory used for constructing new workers * - * @param delta 1 for increment, -1 for decrement + * @return the factory used for constructing new workers */ - final void addActiveCount(int delta) { - long d = delta < 0 ? -AC_UNIT : AC_UNIT; - long c; - do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl, - ((c + d) & AC_MASK) | - (c & ~AC_MASK))); + public ForkJoinWorkerThreadFactory getFactory() { + return factory; } /** - * Returns the approximate (non-atomic) number of idle threads per - * active thread. + * Returns the handler for internal worker threads that terminate + * due to unrecoverable errors encountered while executing tasks. + * @return the handler, or null if none */ - final int idlePerActive() { - // Approximate at powers of two for small values, saturate past 4 - int p = parallelism; - int a = p + (int)(ctl >> AC_SHIFT); - return (a > (p >>>= 1) ? 0 : - a > (p >>>= 1) ? 1 : - a > (p >>>= 1) ? 2 : - a > (p >>>= 1) ? 4 : - 8); + public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { + Thread.UncaughtExceptionHandler h; + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + h = ueh; + } finally { + lock.unlock(); + } + return h; } - // Exported methods - - // Constructors - /** - * Creates a {@code ForkJoinPool} with parallelism equal to {@link - * java.lang.Runtime#availableProcessors}, using the {@linkplain - * #defaultForkJoinWorkerThreadFactory default thread factory}, - * no UncaughtExceptionHandler, and non-async LIFO processing mode. + * Sets the handler for internal worker threads that terminate due + * to unrecoverable errors encountered while executing tasks. + * Unless set, the current default or ThreadGroup handler is used + * as handler. * + * @param h the new handler + * @return the old handler, or null if none * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ - public ForkJoinPool() { - this(Runtime.getRuntime().availableProcessors(), - defaultForkJoinWorkerThreadFactory, null, false); + public Thread.UncaughtExceptionHandler + setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) { + checkPermission(); + Thread.UncaughtExceptionHandler old = null; + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + old = ueh; + ueh = h; + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread w = ws[i]; + if (w != null) + w.setUncaughtExceptionHandler(h); + } + } + } finally { + lock.unlock(); + } + return old; } - /** - * Creates a {@code ForkJoinPool} with the indicated parallelism - * level, the {@linkplain - * #defaultForkJoinWorkerThreadFactory default thread factory}, - * no UncaughtExceptionHandler, and non-async LIFO processing mode. - * - * @param parallelism the parallelism level - * @throws IllegalArgumentException if parallelism less than or - * equal to zero, or greater than implementation limit - * @throws SecurityException if a security manager exists and - * the caller is not permitted to modify threads - * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} - */ - public ForkJoinPool(int parallelism) { - this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); - } /** - * Creates a {@code ForkJoinPool} with the given parameters. - * - * @param parallelism the parallelism level. For default value, - * use {@link java.lang.Runtime#availableProcessors}. - * @param factory the factory for creating new threads. For default value, - * use {@link #defaultForkJoinWorkerThreadFactory}. - * @param handler the handler for internal worker threads that - * terminate due to unrecoverable errors encountered while executing - * tasks. For default value, use {@code null}. - * @param asyncMode if true, - * establishes local first-in-first-out scheduling mode for forked - * tasks that are never joined. This mode may be more appropriate - * than default locally stack-based mode in applications in which - * worker threads only process event-style asynchronous tasks. - * For default value, use {@code false}. + * Sets the target paralleism level of this pool. + * @param parallelism the target parallelism * @throws IllegalArgumentException if parallelism less than or - * equal to zero, or greater than implementation limit - * @throws NullPointerException if the factory is null + * equal to zero or greater than maximum size bounds. * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ - public ForkJoinPool(int parallelism, - ForkJoinWorkerThreadFactory factory, - Thread.UncaughtExceptionHandler handler, - boolean asyncMode) { + public void setParallelism(int parallelism) { checkPermission(); - if (factory == null) - throw new NullPointerException(); - if (parallelism <= 0 || parallelism > MAX_ID) + if (parallelism <= 0 || parallelism > maxPoolSize) throw new IllegalArgumentException(); - this.parallelism = parallelism; - this.factory = factory; - this.ueh = handler; - this.locallyFifo = asyncMode; - long np = (long)(-parallelism); // offset ctl counts - this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); - this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; - // initialize workers array with room for 2*parallelism if possible - int n = parallelism << 1; - if (n >= MAX_ID) - n = MAX_ID; - else { // See Hackers Delight, sec 3.2, where n < (1 << 16) - n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + if (!isTerminating()) { + int p = this.parallelism; + this.parallelism = parallelism; + if (parallelism > p) + createAndStartAddedWorkers(); + else + trimSpares(); + } + } finally { + lock.unlock(); } - workers = new ForkJoinWorkerThread[n + 1]; - this.submissionLock = new ReentrantLock(); - this.termination = submissionLock.newCondition(); - StringBuilder sb = new StringBuilder("ForkJoinPool-"); - sb.append(poolNumberGenerator.incrementAndGet()); - sb.append("-worker-"); - this.workerNamePrefix = sb.toString(); + signalIdleWorkers(); } - // Execution methods - /** - * Performs the given task, returning its result upon completion. - * If the computation encounters an unchecked Exception or Error, - * it is rethrown as the outcome of this invocation. Rethrown - * exceptions behave in the same way as regular exceptions, but, - * when possible, contain stack traces (as displayed for example - * using {@code ex.printStackTrace()}) of both the current thread - * as well as the thread actually encountering the exception; - * minimally only the latter. + * Returns the targeted number of worker threads in this pool. * - * @param task the task - * @return the task's result - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution + * @return the targeted number of worker threads in this pool */ - public <T> T invoke(ForkJoinTask<T> task) { - Thread t = Thread.currentThread(); - if (task == null) - throw new NullPointerException(); - if (shutdown) - throw new RejectedExecutionException(); - if ((t instanceof ForkJoinWorkerThread) && - ((ForkJoinWorkerThread)t).pool == this) - return task.invoke(); // bypass submit if in same pool - else { - addSubmission(task); - return task.join(); - } - } - - /** - * Unless terminating, forks task if within an ongoing FJ - * computation in the current pool, else submits as external task. - */ - private <T> void forkOrSubmit(ForkJoinTask<T> task) { - ForkJoinWorkerThread w; - Thread t = Thread.currentThread(); - if (shutdown) - throw new RejectedExecutionException(); - if ((t instanceof ForkJoinWorkerThread) && - (w = (ForkJoinWorkerThread)t).pool == this) - w.pushTask(task); - else - addSubmission(task); - } - - /** - * Arranges for (asynchronous) execution of the given task. - * - * @param task the task - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution - */ - public void execute(ForkJoinTask<?> task) { - if (task == null) - throw new NullPointerException(); - forkOrSubmit(task); - } - - // AbstractExecutorService methods - - /** - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution - */ - public void execute(Runnable task) { - if (task == null) - throw new NullPointerException(); - ForkJoinTask<?> job; - if (task instanceof ForkJoinTask<?>) // avoid re-wrap - job = (ForkJoinTask<?>) task; - else - job = ForkJoinTask.adapt(task, null); - forkOrSubmit(job); + public int getParallelism() { + return parallelism; } /** - * Submits a ForkJoinTask for execution. + * Returns the number of worker threads that have started but not + * yet terminated. This result returned by this method may differ + * from <code>getParallelism</code> when threads are created to + * maintain parallelism when others are cooperatively blocked. * - * @param task the task to submit - * @return the task - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution - */ - public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { - if (task == null) - throw new NullPointerException(); - forkOrSubmit(task); - return task; - } - - /** - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution - */ - public <T> ForkJoinTask<T> submit(Callable<T> task) { - if (task == null) - throw new NullPointerException(); - ForkJoinTask<T> job = ForkJoinTask.adapt(task); - forkOrSubmit(job); - return job; - } - - /** - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution + * @return the number of worker threads */ - public <T> ForkJoinTask<T> submit(Runnable task, T result) { - if (task == null) - throw new NullPointerException(); - ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); - forkOrSubmit(job); - return job; + public int getPoolSize() { + return totalCountOf(workerCounts); } /** - * @throws NullPointerException if the task is null - * @throws RejectedExecutionException if the task cannot be - * scheduled for execution + * Returns the maximum number of threads allowed to exist in the + * pool, even if there are insufficient unblocked running threads. + * @return the maximum */ - public ForkJoinTask<?> submit(Runnable task) { - if (task == null) - throw new NullPointerException(); - ForkJoinTask<?> job; - if (task instanceof ForkJoinTask<?>) // avoid re-wrap - job = (ForkJoinTask<?>) task; - else - job = ForkJoinTask.adapt(task, null); - forkOrSubmit(job); - return job; + public int getMaximumPoolSize() { + return maxPoolSize; } /** - * @throws NullPointerException {@inheritDoc} - * @throws RejectedExecutionException {@inheritDoc} + * Sets the maximum number of threads allowed to exist in the + * pool, even if there are insufficient unblocked running threads. + * Setting this value has no effect on current pool size. It + * controls construction of new threads. + * @throws IllegalArgumentException if negative or greater then + * internal implementation limit. */ - public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { - ArrayList<ForkJoinTask<T>> forkJoinTasks = - new ArrayList<ForkJoinTask<T>>(tasks.size()); - for (Callable<T> task : tasks) - forkJoinTasks.add(ForkJoinTask.adapt(task)); - invoke(new InvokeAll<T>(forkJoinTasks)); - - @SuppressWarnings({"unchecked", "rawtypes"}) - List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; - return futures; - } - - static final class InvokeAll<T> extends RecursiveAction { - final ArrayList<ForkJoinTask<T>> tasks; - InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } - public void compute() { - try { invokeAll(tasks); } - catch (Exception ignore) {} - } - private static final long serialVersionUID = -7914297376763021607L; + public void setMaximumPoolSize(int newMax) { + if (newMax < 0 || newMax > MAX_THREADS) + throw new IllegalArgumentException(); + maxPoolSize = newMax; } - /** - * Returns the factory used for constructing new workers. - * - * @return the factory used for constructing new workers - */ - public ForkJoinWorkerThreadFactory getFactory() { - return factory; - } /** - * Returns the handler for internal worker threads that terminate - * due to unrecoverable errors encountered while executing tasks. - * - * @return the handler, or {@code null} if none + * Returns true if this pool dynamically maintains its target + * parallelism level. If false, new threads are added only to + * avoid possible starvation. + * This setting is by default true; + * @return true if maintains parallelism */ - public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { - return ueh; + public boolean getMaintainsParallelism() { + return maintainsParallelism; } /** - * Returns the targeted parallelism level of this pool. - * - * @return the targeted parallelism level of this pool + * Sets whether this pool dynamically maintains its target + * parallelism level. If false, new threads are added only to + * avoid possible starvation. + * @param enable true to maintains parallelism */ - public int getParallelism() { - return parallelism; + public void setMaintainsParallelism(boolean enable) { + maintainsParallelism = enable; } /** - * Returns the number of worker threads that have started but not - * yet terminated. The result returned by this method may differ - * from {@link #getParallelism} when threads are created to - * maintain parallelism when others are cooperatively blocked. + * Establishes local first-in-first-out scheduling mode for forked + * tasks that are never joined. This mode may be more appropriate + * than default locally stack-based mode in applications in which + * worker threads only process asynchronous tasks. This method is + * designed to be invoked only when pool is quiescent, and + * typically only before any tasks are submitted. The effects of + * invocations at ather times may be unpredictable. * - * @return the number of worker threads + * @param async if true, use locally FIFO scheduling + * @return the previous mode. */ - public int getPoolSize() { - return parallelism + (short)(ctl >>> TC_SHIFT); + public boolean setAsyncMode(boolean async) { + boolean oldMode = locallyFifo; + locallyFifo = async; + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + t.setAsyncMode(async); + } + } + return oldMode; } /** - * Returns {@code true} if this pool uses local first-in-first-out + * Returns true if this pool uses local first-in-first-out * scheduling mode for forked tasks that are never joined. * - * @return {@code true} if this pool uses async mode + * @return true if this pool uses async mode. */ public boolean getAsyncMode() { return locallyFifo; @@ -1685,41 +861,47 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { /** * Returns an estimate of the number of worker threads that are * not blocked waiting to join tasks or for other managed - * synchronization. This method may overestimate the - * number of running threads. + * synchronization. * * @return the number of worker threads */ public int getRunningThreadCount() { - int r = parallelism + (int)(ctl >> AC_SHIFT); - return (r <= 0) ? 0 : r; // suppress momentarily negative values + return runningCountOf(workerCounts); } /** * Returns an estimate of the number of threads that are currently * stealing or executing tasks. This method may overestimate the * number of active threads. - * - * @return the number of active threads + * @return the number of active threads. */ public int getActiveThreadCount() { - int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount; - return (r <= 0) ? 0 : r; // suppress momentarily negative values + return activeCountOf(runControl); } /** - * Returns {@code true} if all worker threads are currently idle. - * An idle worker is one that cannot obtain a task to execute - * because none are available to steal from other threads, and - * there are no pending submissions to the pool. This method is - * conservative; it might not return {@code true} immediately upon - * idleness of all threads, but will eventually become true if - * threads remain inactive. - * - * @return {@code true} if all threads are currently idle + * Returns an estimate of the number of threads that are currently + * idle waiting for tasks. This method may underestimate the + * number of idle threads. + * @return the number of idle threads. + */ + final int getIdleThreadCount() { + int c = runningCountOf(workerCounts) - activeCountOf(runControl); + return (c <= 0)? 0 : c; + } + + /** + * Returns true if all worker threads are currently idle. An idle + * worker is one that cannot obtain a task to execute because none + * are available to steal from other threads, and there are no + * pending submissions to the pool. This method is conservative: + * It might not return true immediately upon idleness of all + * threads, but will eventually become true if threads remain + * inactive. + * @return true if all threads are currently idle */ public boolean isQuiescent() { - return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0; + return activeCountOf(runControl) == 0; } /** @@ -1727,14 +909,23 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { * one thread's work queue by another. The reported value * underestimates the actual total number of steals when the pool * is not quiescent. This value may be useful for monitoring and - * tuning fork/join programs: in general, steal counts should be + * tuning fork/join programs: In general, steal counts should be * high enough to keep threads busy, but low enough to avoid * overhead and contention across threads. - * - * @return the number of steals + * @return the number of steals. */ public long getStealCount() { - return stealCount; + return stealCount.get(); + } + + /** + * Accumulate steal count from a worker. Call only + * when worker known to be idle. + */ + private void updateStealCount(ForkJoinWorkerThread w) { + int sc = w.getAndClearStealCount(); + if (sc != 0) + stealCount.addAndGet(sc); } /** @@ -1744,99 +935,77 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { * an approximation, obtained by iterating across all threads in * the pool. This method may be useful for tuning task * granularities. - * - * @return the number of queued tasks + * @return the number of queued tasks. */ public long getQueuedTaskCount() { long count = 0; - ForkJoinWorkerThread[] ws; - if ((short)(ctl >>> TC_SHIFT) > -parallelism && - (ws = workers) != null) { - for (ForkJoinWorkerThread w : ws) - if (w != null) - count -= w.queueBase - w.queueTop; // must read base first + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + count += t.getQueueSize(); + } } return count; } /** - * Returns an estimate of the number of tasks submitted to this - * pool that have not yet begun executing. This method may take - * time proportional to the number of submissions. - * - * @return the number of queued submissions + * Returns an estimate of the number tasks submitted to this pool + * that have not yet begun executing. This method takes time + * proportional to the number of submissions. + * @return the number of queued submissions. */ public int getQueuedSubmissionCount() { - return -queueBase + queueTop; + return submissionQueue.size(); } /** - * Returns {@code true} if there are any tasks submitted to this - * pool that have not yet begun executing. - * - * @return {@code true} if there are any queued submissions + * Returns true if there are any tasks submitted to this pool + * that have not yet begun executing. + * @return <code>true</code> if there are any queued submissions. */ public boolean hasQueuedSubmissions() { - return queueBase != queueTop; + return !submissionQueue.isEmpty(); } /** * Removes and returns the next unexecuted submission if one is * available. This method may be useful in extensions to this * class that re-assign work in systems with multiple pools. - * - * @return the next submission, or {@code null} if none + * @return the next submission, or null if none */ protected ForkJoinTask<?> pollSubmission() { - ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; - while ((b = queueBase) != queueTop && - (q = submissionQueue) != null && - (i = (q.length - 1) & b) >= 0) { - long u = (i << ASHIFT) + ABASE; - if ((t = q[i]) != null && - queueBase == b && - UNSAFE.compareAndSwapObject(q, u, t, null)) { - queueBase = b + 1; - return t; - } - } - return null; + return submissionQueue.poll(); } /** * Removes all available unexecuted submitted and forked tasks * from scheduling queues and adds them to the given collection, * without altering their execution status. These may include - * artificially generated or wrapped tasks. This method is - * designed to be invoked only when the pool is known to be + * artifically generated or wrapped tasks. This method id designed + * to be invoked only when the pool is known to be * quiescent. Invocations at other times may not remove all * tasks. A failure encountered while attempting to add elements - * to collection {@code c} may result in elements being in + * to collection <tt>c</tt> may result in elements being in * neither, either or both collections when the associated * exception is thrown. The behavior of this operation is * undefined if the specified collection is modified while the * operation is in progress. - * * @param c the collection to transfer elements into * @return the number of elements transferred */ - protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { - int count = 0; - while (queueBase != queueTop) { - ForkJoinTask<?> t = pollSubmission(); - if (t != null) { - c.add(t); - ++count; - } - } - ForkJoinWorkerThread[] ws; - if ((short)(ctl >>> TC_SHIFT) > -parallelism && - (ws = workers) != null) { - for (ForkJoinWorkerThread w : ws) + protected int drainTasksTo(Collection<ForkJoinTask<?>> c) { + int n = submissionQueue.drainTo(c); + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread w = ws[i]; if (w != null) - count += w.drainTasksTo(c); + n += w.drainTasksTo(c); + } } - return count; + return n; } /** @@ -1847,118 +1016,101 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { * @return a string identifying this pool, as well as its state */ public String toString() { + int ps = parallelism; + int wc = workerCounts; + int rc = runControl; long st = getStealCount(); long qt = getQueuedTaskCount(); long qs = getQueuedSubmissionCount(); - int pc = parallelism; - long c = ctl; - int tc = pc + (short)(c >>> TC_SHIFT); - int rc = pc + (int)(c >> AC_SHIFT); - if (rc < 0) // ignore transient negative - rc = 0; - int ac = rc + blockedCount; - String level; - if ((c & STOP_BIT) != 0) - level = (tc == 0) ? "Terminated" : "Terminating"; - else - level = shutdown ? "Shutting down" : "Running"; return super.toString() + - "[" + level + - ", parallelism = " + pc + - ", size = " + tc + - ", active = " + ac + - ", running = " + rc + + "[" + runStateToString(runStateOf(rc)) + + ", parallelism = " + ps + + ", size = " + totalCountOf(wc) + + ", active = " + activeCountOf(rc) + + ", running = " + runningCountOf(wc) + ", steals = " + st + ", tasks = " + qt + ", submissions = " + qs + "]"; } + private static String runStateToString(int rs) { + switch(rs) { + case RUNNING: return "Running"; + case SHUTDOWN: return "Shutting down"; + case TERMINATING: return "Terminating"; + case TERMINATED: return "Terminated"; + default: throw new Error("Unknown run state"); + } + } + + // lifecycle control + /** * Initiates an orderly shutdown in which previously submitted * tasks are executed, but no new tasks will be accepted. * Invocation has no additional effect if already shut down. * Tasks that are in the process of being submitted concurrently * during the course of this method may or may not be rejected. - * * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ public void shutdown() { checkPermission(); - shutdown = true; - tryTerminate(false); + transitionRunStateTo(SHUTDOWN); + if (canTerminateOnShutdown(runControl)) + terminateOnShutdown(); } /** - * Attempts to cancel and/or stop all tasks, and reject all - * subsequently submitted tasks. Tasks that are in the process of - * being submitted or executed concurrently during the course of - * this method may or may not be rejected. This method cancels - * both existing and unexecuted tasks, in order to permit - * termination in the presence of task dependencies. So the method - * always returns an empty list (unlike the case for some other - * Executors). - * + * Attempts to stop all actively executing tasks, and cancels all + * waiting tasks. Tasks that are in the process of being + * submitted or executed concurrently during the course of this + * method may or may not be rejected. Unlike some other executors, + * this method cancels rather than collects non-executed tasks + * upon termination, so always returns an empty list. However, you + * can use method <code>drainTasksTo</code> before invoking this + * method to transfer unexecuted tasks to another collection. * @return an empty list * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link - * java.lang.RuntimePermission}{@code ("modifyThread")} + * java.lang.RuntimePermission}<code>("modifyThread")</code>, */ public List<Runnable> shutdownNow() { checkPermission(); - shutdown = true; - tryTerminate(true); + terminate(); return Collections.emptyList(); } /** - * Returns {@code true} if all tasks have completed following shut down. + * Returns <code>true</code> if all tasks have completed following shut down. * - * @return {@code true} if all tasks have completed following shut down + * @return <code>true</code> if all tasks have completed following shut down */ public boolean isTerminated() { - long c = ctl; - return ((c & STOP_BIT) != 0L && - (short)(c >>> TC_SHIFT) == -parallelism); + return runStateOf(runControl) == TERMINATED; } /** - * Returns {@code true} if the process of termination has - * commenced but not yet completed. This method may be useful for - * debugging. A return of {@code true} reported a sufficient - * period after shutdown may indicate that submitted tasks have - * ignored or suppressed interruption, or are waiting for IO, - * causing this executor not to properly terminate. (See the - * advisory notes for class {@link ForkJoinTask} stating that - * tasks should not normally entail blocking operations. But if - * they do, they must abort them on interrupt.) + * Returns <code>true</code> if the process of termination has + * commenced but possibly not yet completed. * - * @return {@code true} if terminating but not yet terminated + * @return <code>true</code> if terminating */ public boolean isTerminating() { - long c = ctl; - return ((c & STOP_BIT) != 0L && - (short)(c >>> TC_SHIFT) != -parallelism); + return runStateOf(runControl) >= TERMINATING; } /** - * Returns true if terminating or terminated. Used by ForkJoinWorkerThread. - */ - final boolean isAtLeastTerminating() { - return (ctl & STOP_BIT) != 0L; - } - - /** - * Returns {@code true} if this pool has been shut down. + * Returns <code>true</code> if this pool has been shut down. * - * @return {@code true} if this pool has been shut down + * @return <code>true</code> if this pool has been shut down */ public boolean isShutdown() { - return shutdown; + return runStateOf(runControl) >= SHUTDOWN; } /** @@ -1968,14 +1120,14 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { * * @param timeout the maximum time to wait * @param unit the time unit of the timeout argument - * @return {@code true} if this executor terminated and - * {@code false} if the timeout elapsed before termination + * @return <code>true</code> if this executor terminated and + * <code>false</code> if the timeout elapsed before termination * @throws InterruptedException if interrupted while waiting */ public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException { long nanos = unit.toNanos(timeout); - final ReentrantLock lock = this.submissionLock; + final ReentrantLock lock = this.workerLock; lock.lock(); try { for (;;) { @@ -1990,165 +1142,729 @@ public class ForkJoinPool /*extends AbstractExecutorService*/ { } } + // Shutdown and termination support + + /** + * Callback from terminating worker. Null out the corresponding + * workers slot, and if terminating, try to terminate, else try to + * shrink workers array. + * @param w the worker + */ + final void workerTerminated(ForkJoinWorkerThread w) { + updateStealCount(w); + updateWorkerCount(-1); + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + int idx = w.poolIndex; + if (idx >= 0 && idx < ws.length && ws[idx] == w) + ws[idx] = null; + if (totalCountOf(workerCounts) == 0) { + terminate(); // no-op if already terminating + transitionRunStateTo(TERMINATED); + termination.signalAll(); + } + else if (!isTerminating()) { + tryShrinkWorkerArray(); + tryResumeSpare(true); // allow replacement + } + } + } finally { + lock.unlock(); + } + signalIdleWorkers(); + } + + /** + * Initiate termination. + */ + private void terminate() { + if (transitionRunStateTo(TERMINATING)) { + stopAllWorkers(); + resumeAllSpares(); + signalIdleWorkers(); + cancelQueuedSubmissions(); + cancelQueuedWorkerTasks(); + interruptUnterminatedWorkers(); + signalIdleWorkers(); // resignal after interrupt + } + } + + /** + * Possibly terminate when on shutdown state + */ + private void terminateOnShutdown() { + if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) + terminate(); + } + + /** + * Clear out and cancel submissions + */ + private void cancelQueuedSubmissions() { + ForkJoinTask<?> task; + while ((task = pollSubmission()) != null) + task.cancel(false); + } + + /** + * Clean out worker queues. + */ + private void cancelQueuedWorkerTasks() { + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + t.cancelTasks(); + } + } + } finally { + lock.unlock(); + } + } + + /** + * Set each worker's status to terminating. Requires lock to avoid + * conflicts with add/remove + */ + private void stopAllWorkers() { + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null) + t.shutdownNow(); + } + } + } finally { + lock.unlock(); + } + } + + /** + * Interrupt all unterminated workers. This is not required for + * sake of internal control, but may help unstick user code during + * shutdown. + */ + private void interruptUnterminatedWorkers() { + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (int i = 0; i < ws.length; ++i) { + ForkJoinWorkerThread t = ws[i]; + if (t != null && !t.isTerminated()) { + try { + t.interrupt(); + } catch (SecurityException ignore) { + } + } + } + } + } finally { + lock.unlock(); + } + } + + + /* + * Nodes for event barrier to manage idle threads. Queue nodes + * are basic Treiber stack nodes, also used for spare stack. + * + * The event barrier has an event count and a wait queue (actually + * a Treiber stack). Workers are enabled to look for work when + * the eventCount is incremented. If they fail to find work, they + * may wait for next count. Upon release, threads help others wake + * up. + * + * Synchronization events occur only in enough contexts to + * maintain overall liveness: + * + * - Submission of a new task to the pool + * - Resizes or other changes to the workers array + * - pool termination + * - A worker pushing a task on an empty queue + * + * The case of pushing a task occurs often enough, and is heavy + * enough compared to simple stack pushes, to require special + * handling: Method signalWork returns without advancing count if + * the queue appears to be empty. This would ordinarily result in + * races causing some queued waiters not to be woken up. To avoid + * this, the first worker enqueued in method sync (see + * syncIsReleasable) rescans for tasks after being enqueued, and + * helps signal if any are found. This works well because the + * worker has nothing better to do, and so might as well help + * alleviate the overhead and contention on the threads actually + * doing work. Also, since event counts increments on task + * availability exist to maintain liveness (rather than to force + * refreshes etc), it is OK for callers to exit early if + * contending with another signaller. + */ + static final class WaitQueueNode { + WaitQueueNode next; // only written before enqueued + volatile ForkJoinWorkerThread thread; // nulled to cancel wait + final long count; // unused for spare stack + + WaitQueueNode(long c, ForkJoinWorkerThread w) { + count = c; + thread = w; + } + + /** + * Wake up waiter, returning false if known to already + */ + boolean signal() { + ForkJoinWorkerThread t = thread; + if (t == null) + return false; + thread = null; + LockSupport.unpark(t); + return true; + } + + /** + * Await release on sync + */ + void awaitSyncRelease(ForkJoinPool p) { + while (thread != null && !p.syncIsReleasable(this)) + LockSupport.park(this); + } + + /** + * Await resumption as spare + */ + void awaitSpareRelease() { + while (thread != null) { + if (!Thread.interrupted()) + LockSupport.park(this); + } + } + } + + /** + * Ensures that no thread is waiting for count to advance from the + * current value of eventCount read on entry to this method, by + * releasing waiting threads if necessary. + * @return the count + */ + final long ensureSync() { + long c = eventCount; + WaitQueueNode q; + while ((q = syncStack) != null && q.count < c) { + if (casBarrierStack(q, null)) { + do { + q.signal(); + } while ((q = q.next) != null); + break; + } + } + return c; + } + + /** + * Increments event count and releases waiting threads. + */ + private void signalIdleWorkers() { + long c; + do;while (!casEventCount(c = eventCount, c+1)); + ensureSync(); + } + + /** + * Signal threads waiting to poll a task. Because method sync + * rechecks availability, it is OK to only proceed if queue + * appears to be non-empty, and OK to skip under contention to + * increment count (since some other thread succeeded). + */ + final void signalWork() { + long c; + WaitQueueNode q; + if (syncStack != null && + casEventCount(c = eventCount, c+1) && + (((q = syncStack) != null && q.count <= c) && + (!casBarrierStack(q, q.next) || !q.signal()))) + ensureSync(); + } + + /** + * Waits until event count advances from last value held by + * caller, or if excess threads, caller is resumed as spare, or + * caller or pool is terminating. Updates caller's event on exit. + * @param w the calling worker thread + */ + final void sync(ForkJoinWorkerThread w) { + updateStealCount(w); // Transfer w's count while it is idle + + while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { + long prev = w.lastEventCount; + WaitQueueNode node = null; + WaitQueueNode h; + while (eventCount == prev && + ((h = syncStack) == null || h.count == prev)) { + if (node == null) + node = new WaitQueueNode(prev, w); + if (casBarrierStack(node.next = h, node)) { + node.awaitSyncRelease(this); + break; + } + } + long ec = ensureSync(); + if (ec != prev) { + w.lastEventCount = ec; + break; + } + } + } + + /** + * Returns true if worker waiting on sync can proceed: + * - on signal (thread == null) + * - on event count advance (winning race to notify vs signaller) + * - on Interrupt + * - if the first queued node, we find work available + * If node was not signalled and event count not advanced on exit, + * then we also help advance event count. + * @return true if node can be released + */ + final boolean syncIsReleasable(WaitQueueNode node) { + long prev = node.count; + if (!Thread.interrupted() && node.thread != null && + (node.next != null || + !ForkJoinWorkerThread.hasQueuedTasks(workers)) && + eventCount == prev) + return false; + if (node.thread != null) { + node.thread = null; + long ec = eventCount; + if (prev <= ec) // help signal + casEventCount(ec, ec+1); + } + return true; + } + + /** + * Returns true if a new sync event occurred since last call to + * sync or this method, if so, updating caller's count. + */ + final boolean hasNewSyncEvent(ForkJoinWorkerThread w) { + long lc = w.lastEventCount; + long ec = ensureSync(); + if (ec == lc) + return false; + w.lastEventCount = ec; + return true; + } + + // Parallelism maintenance + + /** + * Decrement running count; if too low, add spare. + * + * Conceptually, all we need to do here is add or resume a + * spare thread when one is about to block (and remove or + * suspend it later when unblocked -- see suspendIfSpare). + * However, implementing this idea requires coping with + * several problems: We have imperfect information about the + * states of threads. Some count updates can and usually do + * lag run state changes, despite arrangements to keep them + * accurate (for example, when possible, updating counts + * before signalling or resuming), especially when running on + * dynamic JVMs that don't optimize the infrequent paths that + * update counts. Generating too many threads can make these + * problems become worse, because excess threads are more + * likely to be context-switched with others, slowing them all + * down, especially if there is no work available, so all are + * busy scanning or idling. Also, excess spare threads can + * only be suspended or removed when they are idle, not + * immediately when they aren't needed. So adding threads will + * raise parallelism level for longer than necessary. Also, + * FJ applications often enounter highly transient peaks when + * many threads are blocked joining, but for less time than it + * takes to create or resume spares. + * + * @param joinMe if non-null, return early if done + * @param maintainParallelism if true, try to stay within + * target counts, else create only to avoid starvation + * @return true if joinMe known to be done + */ + final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) { + maintainParallelism &= maintainsParallelism; // overrride + boolean dec = false; // true when running count decremented + while (spareStack == null || !tryResumeSpare(dec)) { + int counts = workerCounts; + if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat + if (!needSpare(counts, maintainParallelism)) + break; + if (joinMe.status < 0) + return true; + if (tryAddSpare(counts)) + break; + } + } + return false; + } + + /** + * Same idea as preJoin + */ + final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){ + maintainParallelism &= maintainsParallelism; + boolean dec = false; + while (spareStack == null || !tryResumeSpare(dec)) { + int counts = workerCounts; + if (dec || (dec = casWorkerCounts(counts, --counts))) { + if (!needSpare(counts, maintainParallelism)) + break; + if (blocker.isReleasable()) + return true; + if (tryAddSpare(counts)) + break; + } + } + return false; + } + + /** + * Returns true if a spare thread appears to be needed. If + * maintaining parallelism, returns true when the deficit in + * running threads is more than the surplus of total threads, and + * there is apparently some work to do. This self-limiting rule + * means that the more threads that have already been added, the + * less parallelism we will tolerate before adding another. + * @param counts current worker counts + * @param maintainParallelism try to maintain parallelism + */ + private boolean needSpare(int counts, boolean maintainParallelism) { + int ps = parallelism; + int rc = runningCountOf(counts); + int tc = totalCountOf(counts); + int runningDeficit = ps - rc; + int totalSurplus = tc - ps; + return (tc < maxPoolSize && + (rc == 0 || totalSurplus < 0 || + (maintainParallelism && + runningDeficit > totalSurplus && + ForkJoinWorkerThread.hasQueuedTasks(workers)))); + } + + /** + * Add a spare worker if lock available and no more than the + * expected numbers of threads exist + * @return true if successful + */ + private boolean tryAddSpare(int expectedCounts) { + final ReentrantLock lock = this.workerLock; + int expectedRunning = runningCountOf(expectedCounts); + int expectedTotal = totalCountOf(expectedCounts); + boolean success = false; + boolean locked = false; + // confirm counts while locking; CAS after obtaining lock + try { + for (;;) { + int s = workerCounts; + int tc = totalCountOf(s); + int rc = runningCountOf(s); + if (rc > expectedRunning || tc > expectedTotal) + break; + if (!locked && !(locked = lock.tryLock())) + break; + if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) { + createAndStartSpare(tc); + success = true; + break; + } + } + } finally { + if (locked) + lock.unlock(); + } + return success; + } + + /** + * Add the kth spare worker. On entry, pool coounts are already + * adjusted to reflect addition. + */ + private void createAndStartSpare(int k) { + ForkJoinWorkerThread w = null; + ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1); + int len = ws.length; + // Probably, we can place at slot k. If not, find empty slot + if (k < len && ws[k] != null) { + for (k = 0; k < len && ws[k] != null; ++k) + ; + } + if (k < len && !isTerminating() && (w = createWorker(k)) != null) { + ws[k] = w; + w.start(); + } + else + updateWorkerCount(-1); // adjust on failure + signalIdleWorkers(); + } + + /** + * Suspend calling thread w if there are excess threads. Called + * only from sync. Spares are enqueued in a Treiber stack + * using the same WaitQueueNodes as barriers. They are resumed + * mainly in preJoin, but are also woken on pool events that + * require all threads to check run state. + * @param w the caller + */ + private boolean suspendIfSpare(ForkJoinWorkerThread w) { + WaitQueueNode node = null; + int s; + while (parallelism < runningCountOf(s = workerCounts)) { + if (node == null) + node = new WaitQueueNode(0, w); + if (casWorkerCounts(s, s-1)) { // representation-dependent + // push onto stack + do;while (!casSpareStack(node.next = spareStack, node)); + // block until released by resumeSpare + node.awaitSpareRelease(); + return true; + } + } + return false; + } + + /** + * Try to pop and resume a spare thread. + * @param updateCount if true, increment running count on success + * @return true if successful + */ + private boolean tryResumeSpare(boolean updateCount) { + WaitQueueNode q; + while ((q = spareStack) != null) { + if (casSpareStack(q, q.next)) { + if (updateCount) + updateRunningCount(1); + q.signal(); + return true; + } + } + return false; + } + + /** + * Pop and resume all spare threads. Same idea as ensureSync. + * @return true if any spares released + */ + private boolean resumeAllSpares() { + WaitQueueNode q; + while ( (q = spareStack) != null) { + if (casSpareStack(q, null)) { + do { + updateRunningCount(1); + q.signal(); + } while ((q = q.next) != null); + return true; + } + } + return false; + } + + /** + * Pop and shutdown excessive spare threads. Call only while + * holding lock. This is not guaranteed to eliminate all excess + * threads, only those suspended as spares, which are the ones + * unlikely to be needed in the future. + */ + private void trimSpares() { + int surplus = totalCountOf(workerCounts) - parallelism; + WaitQueueNode q; + while (surplus > 0 && (q = spareStack) != null) { + if (casSpareStack(q, null)) { + do { + updateRunningCount(1); + ForkJoinWorkerThread w = q.thread; + if (w != null && surplus > 0 && + runningCountOf(workerCounts) > 0 && w.shutdown()) + --surplus; + q.signal(); + } while ((q = q.next) != null); + } + } + } + /** * Interface for extending managed parallelism for tasks running - * in {@link ForkJoinPool}s. - * - * <p>A {@code ManagedBlocker} provides two methods. Method - * {@code isReleasable} must return {@code true} if blocking is - * not necessary. Method {@code block} blocks the current thread - * if necessary (perhaps internally invoking {@code isReleasable} - * before actually blocking). These actions are performed by any - * thread invoking {@link ForkJoinPool#managedBlock}. The - * unusual methods in this API accommodate synchronizers that may, - * but don't usually, block for long periods. Similarly, they - * allow more efficient internal handling of cases in which - * additional workers may be, but usually are not, needed to - * ensure sufficient parallelism. Toward this end, - * implementations of method {@code isReleasable} must be amenable - * to repeated invocation. - * + * in ForkJoinPools. A ManagedBlocker provides two methods. + * Method <code>isReleasable</code> must return true if blocking is not + * necessary. Method <code>block</code> blocks the current thread + * if necessary (perhaps internally invoking isReleasable before + * actually blocking.). * <p>For example, here is a ManagedBlocker based on a * ReentrantLock: - * <pre> {@code - * class ManagedLocker implements ManagedBlocker { - * final ReentrantLock lock; - * boolean hasLock = false; - * ManagedLocker(ReentrantLock lock) { this.lock = lock; } - * public boolean block() { - * if (!hasLock) - * lock.lock(); - * return true; - * } - * public boolean isReleasable() { - * return hasLock || (hasLock = lock.tryLock()); - * } - * }}</pre> - * - * <p>Here is a class that possibly blocks waiting for an - * item on a given queue: - * <pre> {@code - * class QueueTaker<E> implements ManagedBlocker { - * final BlockingQueue<E> queue; - * volatile E item = null; - * QueueTaker(BlockingQueue<E> q) { this.queue = q; } - * public boolean block() throws InterruptedException { - * if (item == null) - * item = queue.take(); - * return true; + * <pre> + * class ManagedLocker implements ManagedBlocker { + * final ReentrantLock lock; + * boolean hasLock = false; + * ManagedLocker(ReentrantLock lock) { this.lock = lock; } + * public boolean block() { + * if (!hasLock) + * lock.lock(); + * return true; + * } + * public boolean isReleasable() { + * return hasLock || (hasLock = lock.tryLock()); + * } * } - * public boolean isReleasable() { - * return item != null || (item = queue.poll()) != null; - * } - * public E getItem() { // call after pool.managedBlock completes - * return item; - * } - * }}</pre> + * </pre> */ public static interface ManagedBlocker { /** * Possibly blocks the current thread, for example waiting for * a lock or condition. - * - * @return {@code true} if no additional blocking is necessary - * (i.e., if isReleasable would return true) + * @return true if no additional blocking is necessary (i.e., + * if isReleasable would return true). * @throws InterruptedException if interrupted while waiting - * (the method is not required to do so, but is allowed to) + * (the method is not required to do so, but is allowe to). */ boolean block() throws InterruptedException; /** - * Returns {@code true} if blocking is unnecessary. + * Returns true if blocking is unnecessary. */ boolean isReleasable(); } /** * Blocks in accord with the given blocker. If the current thread - * is a {@link ForkJoinWorkerThread}, this method possibly - * arranges for a spare thread to be activated if necessary to - * ensure sufficient parallelism while the current thread is blocked. - * - * <p>If the caller is not a {@link ForkJoinTask}, this method is - * behaviorally equivalent to - * <pre> {@code - * while (!blocker.isReleasable()) - * if (blocker.block()) - * return; - * }</pre> - * - * If the caller is a {@code ForkJoinTask}, then the pool may - * first be expanded to ensure parallelism, and later adjusted. + * is a ForkJoinWorkerThread, this method possibly arranges for a + * spare thread to be activated if necessary to ensure parallelism + * while the current thread is blocked. If + * <code>maintainParallelism</code> is true and the pool supports + * it ({@link #getMaintainsParallelism}), this method attempts to + * maintain the pool's nominal parallelism. Otherwise if activates + * a thread only if necessary to avoid complete starvation. This + * option may be preferable when blockages use timeouts, or are + * almost always brief. + * + * <p> If the caller is not a ForkJoinTask, this method is behaviorally + * equivalent to + * <pre> + * while (!blocker.isReleasable()) + * if (blocker.block()) + * return; + * </pre> + * If the caller is a ForkJoinTask, then the pool may first + * be expanded to ensure parallelism, and later adjusted. * * @param blocker the blocker - * @throws InterruptedException if blocker.block did so - */ - public static void managedBlock(ManagedBlocker blocker) + * @param maintainParallelism if true and supported by this pool, + * attempt to maintain the pool's nominal parallelism; otherwise + * activate a thread only if necessary to avoid complete + * starvation. + * @throws InterruptedException if blocker.block did so. + */ + public static void managedBlock(ManagedBlocker blocker, + boolean maintainParallelism) throws InterruptedException { Thread t = Thread.currentThread(); - if (t instanceof ForkJoinWorkerThread) { - ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; - w.pool.awaitBlocker(blocker); - } - else { - do {} while (!blocker.isReleasable() && !blocker.block()); + ForkJoinPool pool = (t instanceof ForkJoinWorkerThread? + ((ForkJoinWorkerThread)t).pool : null); + if (!blocker.isReleasable()) { + try { + if (pool == null || + !pool.preBlock(blocker, maintainParallelism)) + awaitBlocker(blocker); + } finally { + if (pool != null) + pool.updateRunningCount(1); + } } } - // AbstractExecutorService overrides. These rely on undocumented - // fact that ForkJoinTask.adapt returns ForkJoinTasks that also - // implement RunnableFuture. + private static void awaitBlocker(ManagedBlocker blocker) + throws InterruptedException { + do;while (!blocker.isReleasable() && !blocker.block()); + } + + // AbstractExecutorService overrides protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { - return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); + return new AdaptedRunnable(runnable, value); } protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { - return (RunnableFuture<T>) ForkJoinTask.adapt(callable); + return new AdaptedCallable(callable); } - // Unsafe mechanics - private static final sun.misc.Unsafe UNSAFE; - private static final long ctlOffset; - private static final long stealCountOffset; - private static final long blockedCountOffset; - private static final long quiescerCountOffset; - private static final long scanGuardOffset; - private static final long nextWorkerNumberOffset; - private static final long ABASE; - private static final int ASHIFT; + + // Temporary Unsafe mechanics for preliminary release + private static Unsafe getUnsafe() throws Throwable { + try { + return Unsafe.getUnsafe(); + } catch (SecurityException se) { + try { + return java.security.AccessController.doPrivileged + (new java.security.PrivilegedExceptionAction<Unsafe>() { + public Unsafe run() throws Exception { + return getUnsafePrivileged(); + }}); + } catch (java.security.PrivilegedActionException e) { + throw e.getCause(); + } + } + } + + private static Unsafe getUnsafePrivileged() + throws NoSuchFieldException, IllegalAccessException { + Field f = Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (Unsafe) f.get(null); + } + + private static long fieldOffset(String fieldName) + throws NoSuchFieldException { + return _unsafe.objectFieldOffset + (ForkJoinPool.class.getDeclaredField(fieldName)); + } + + static final Unsafe _unsafe; + static final long eventCountOffset; + static final long workerCountsOffset; + static final long runControlOffset; + static final long syncStackOffset; + static final long spareStackOffset; static { - poolNumberGenerator = new AtomicInteger(); - workerSeedGenerator = new Random(); - modifyThreadPermission = new RuntimePermission("modifyThread"); - defaultForkJoinWorkerThreadFactory = - new DefaultForkJoinWorkerThreadFactory(); - int s; try { - UNSAFE = sun.misc.Unsafe.getUnsafe(); - Class k = ForkJoinPool.class; - ctlOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("ctl")); - stealCountOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("stealCount")); - blockedCountOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("blockedCount")); - quiescerCountOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("quiescerCount")); - scanGuardOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("scanGuard")); - nextWorkerNumberOffset = UNSAFE.objectFieldOffset - (k.getDeclaredField("nextWorkerNumber")); - Class a = ForkJoinTask[].class; - ABASE = UNSAFE.arrayBaseOffset(a); - s = UNSAFE.arrayIndexScale(a); - } catch (Exception e) { - throw new Error(e); + _unsafe = getUnsafe(); + eventCountOffset = fieldOffset("eventCount"); + workerCountsOffset = fieldOffset("workerCounts"); + runControlOffset = fieldOffset("runControl"); + syncStackOffset = fieldOffset("syncStack"); + spareStackOffset = fieldOffset("spareStack"); + } catch (Throwable e) { + throw new RuntimeException("Could not initialize intrinsics", e); } - if ((s & (s-1)) != 0) - throw new Error("data type scale not a power of two"); - ASHIFT = 31 - Integer.numberOfLeadingZeros(s); } + private boolean casEventCount(long cmp, long val) { + return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val); + } + private boolean casWorkerCounts(int cmp, int val) { + return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val); + } + private boolean casRunControl(int cmp, int val) { + return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val); + } + private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) { + return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val); + } + private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { + return _unsafe.compareAndSwapObject(this, syncStackOffset, cmp, val); + } } |