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Diffstat (limited to 'src/actors/scala/actors/threadpool/locks/ReadWriteLock.java')
| -rw-r--r-- | src/actors/scala/actors/threadpool/locks/ReadWriteLock.java | 104 |
1 files changed, 0 insertions, 104 deletions
diff --git a/src/actors/scala/actors/threadpool/locks/ReadWriteLock.java b/src/actors/scala/actors/threadpool/locks/ReadWriteLock.java deleted file mode 100644 index 02983f9bd4..0000000000 --- a/src/actors/scala/actors/threadpool/locks/ReadWriteLock.java +++ /dev/null @@ -1,104 +0,0 @@ -/* - * 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/licenses/publicdomain - */ - -package scala.actors.threadpool.locks; - -/** - * A <tt>ReadWriteLock</tt> maintains a pair of associated {@link - * Lock locks}, one for read-only operations and one for writing. - * The {@link #readLock read lock} may be held simultaneously by - * multiple reader threads, so long as there are no writers. The - * {@link #writeLock write lock} is exclusive. - * - * <p>All <tt>ReadWriteLock</tt> implementations must guarantee that - * the memory synchronization effects of <tt>writeLock</tt> operations - * (as specified in the {@link Lock} interface) also hold with respect - * to the associated <tt>readLock</tt>. That is, a thread successfully - * acquiring the read lock will see all updates made upon previous - * release of the write lock. - * - * <p>A read-write lock allows for a greater level of concurrency in - * accessing shared data than that permitted by a mutual exclusion lock. - * It exploits the fact that while only a single thread at a time (a - * <em>writer</em> thread) can modify the shared data, in many cases any - * number of threads can concurrently read the data (hence <em>reader</em> - * threads). - * In theory, the increase in concurrency permitted by the use of a read-write - * lock will lead to performance improvements over the use of a mutual - * exclusion lock. In practice this increase in concurrency will only be fully - * realized on a multi-processor, and then only if the access patterns for - * the shared data are suitable. - * - * <p>Whether or not a read-write lock will improve performance over the use - * of a mutual exclusion lock depends on the frequency that the data is - * read compared to being modified, the duration of the read and write - * operations, and the contention for the data - that is, the number of - * threads that will try to read or write the data at the same time. - * For example, a collection that is initially populated with data and - * thereafter infrequently modified, while being frequently searched - * (such as a directory of some kind) is an ideal candidate for the use of - * a read-write lock. However, if updates become frequent then the data - * spends most of its time being exclusively locked and there is little, if any - * increase in concurrency. Further, if the read operations are too short - * the overhead of the read-write lock implementation (which is inherently - * more complex than a mutual exclusion lock) can dominate the execution - * cost, particularly as many read-write lock implementations still serialize - * all threads through a small section of code. Ultimately, only profiling - * and measurement will establish whether the use of a read-write lock is - * suitable for your application. - * - * - * <p>Although the basic operation of a read-write lock is straight-forward, - * there are many policy decisions that an implementation must make, which - * may affect the effectiveness of the read-write lock in a given application. - * Examples of these policies include: - * <ul> - * <li>Determining whether to grant the read lock or the write lock, when - * both readers and writers are waiting, at the time that a writer releases - * the write lock. Writer preference is common, as writes are expected to be - * short and infrequent. Reader preference is less common as it can lead to - * lengthy delays for a write if the readers are frequent and long-lived as - * expected. Fair, or "in-order" implementations are also possible. - * - * <li>Determining whether readers that request the read lock while a - * reader is active and a writer is waiting, are granted the read lock. - * Preference to the reader can delay the writer indefinitely, while - * preference to the writer can reduce the potential for concurrency. - * - * <li>Determining whether the locks are reentrant: can a thread with the - * write lock reacquire it? Can it acquire a read lock while holding the - * write lock? Is the read lock itself reentrant? - * - * <li>Can the write lock be downgraded to a read lock without allowing - * an intervening writer? Can a read lock be upgraded to a write lock, - * in preference to other waiting readers or writers? - * - * </ul> - * You should consider all of these things when evaluating the suitability - * of a given implementation for your application. - * - * @see ReentrantReadWriteLock - * @see Lock - * @see ReentrantLock - * - * @since 1.5 - * @author Doug Lea - */ -public interface ReadWriteLock { - /** - * Returns the lock used for reading. - * - * @return the lock used for reading. - */ - Lock readLock(); - - /** - * Returns the lock used for writing. - * - * @return the lock used for writing. - */ - Lock writeLock(); -} |