/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.concurrent
import java.util.concurrent.{ ExecutorService, Executor }
import scala.annotation.implicitNotFound
/**
* An `ExecutionContext` can execute program logic asynchronously,
* typically but not necessarily on a thread pool.
*
* A general purpose `ExecutionContext` must be asynchronous in executing
* any `Runnable` that is passed into its `execute`-method. A special purpose
* `ExecutionContext` may be synchronous but must only be passed to code that
* is explicitly safe to be run using a synchronously executing `ExecutionContext`.
*
* APIs such as `Future.onComplete` require you to provide a callback
* and an implicit `ExecutionContext`. The implicit `ExecutionContext`
* will be used to execute the callback.
*
* While it is possible to simply import
* `scala.concurrent.ExecutionContext.Implicits.global` to obtain an
* implicit `ExecutionContext`, application developers should carefully
* consider where they want to set execution policy;
* ideally, one place per application—or per logically related section of code—
* will make a decision about which `ExecutionContext` to use.
* That is, you will mostly want to avoid hardcoding, especially via an import,
* `scala.concurrent.ExecutionContext.Implicits.global`.
* The recommended approach is to add `(implicit ec: ExecutionContext)` to methods,
* or class constructor parameters, which need an `ExecutionContext`.
*
* Then locally import a specific `ExecutionContext` in one place for the entire
* application or module, passing it implicitly to individual methods.
* Alternatively define a local implicit val with the required `ExecutionContext`.
*
* A custom `ExecutionContext` may be appropriate to execute code
* which blocks on IO or performs long-running computations.
* `ExecutionContext.fromExecutorService` and `ExecutionContext.fromExecutor`
* are good ways to create a custom `ExecutionContext`.
*
* The intent of `ExecutionContext` is to lexically scope code execution.
* That is, each method, class, file, package, or application determines
* how to run its own code. This avoids issues such as running
* application callbacks on a thread pool belonging to a networking library.
* The size of a networking library's thread pool can be safely configured,
* knowing that only that library's network operations will be affected.
* Application callback execution can be configured separately.
*/
@implicitNotFound("""Cannot find an implicit ExecutionContext. You might pass
an (implicit ec: ExecutionContext) parameter to your method
or import scala.concurrent.ExecutionContext.Implicits.global.""")
trait ExecutionContext {
/** Runs a block of code on this execution context.
*
* @param runnable the task to execute
*/
def execute(runnable: Runnable): Unit
/** Reports that an asynchronous computation failed.
*
* @param cause the cause of the failure
*/
def reportFailure(@deprecatedName('t) cause: Throwable): Unit
/** Prepares for the execution of a task. Returns the prepared
* execution context. The recommended implementation of
* `prepare` is to return `this`.
*
* This method should no longer be overridden or called. It was
* originally expected that `prepare` would be called by
* all libraries that consume ExecutionContexts, in order to
* capture thread local context. However, this usage has proven
* difficult to implement in practice and instead it is
* now better to avoid using `prepare` entirely.
*
* Instead, if an `ExecutionContext` needs to capture thread
* local context, it should capture that context when it is
* constructed, so that it doesn't need any additional
* preparation later.
*/
@deprecated("preparation of ExecutionContexts will be removed", "2.12.0")
def prepare(): ExecutionContext = this
}
/**
* An [[ExecutionContext]] that is also a
* Java [[http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executor.html Executor]].
*/
trait ExecutionContextExecutor extends ExecutionContext with Executor
/**
* An [[ExecutionContext]] that is also a
* Java [[http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html ExecutorService]].
*/
trait ExecutionContextExecutorService extends ExecutionContextExecutor with ExecutorService
/** Contains factory methods for creating execution contexts.
*/
object ExecutionContext {
/**
* The explicit global `ExecutionContext`. Invoke `global` when you want to provide the global
* `ExecutionContext` explicitly.
*
* The default `ExecutionContext` implementation is backed by a work-stealing thread pool.
* It can be configured via the following [[scala.sys.SystemProperties]]:
*
* `scala.concurrent.context.minThreads` = defaults to "1"
* `scala.concurrent.context.numThreads` = defaults to "x1" (i.e. the current number of available processors * 1)
* `scala.concurrent.context.maxThreads` = defaults to "x1" (i.e. the current number of available processors * 1)
* `scala.concurrent.context.maxExtraThreads` = defaults to "256"
*
* The pool size of threads is then `numThreads` bounded by `minThreads` on the lower end and `maxThreads` on the high end.
*
* The `maxExtraThreads` is the maximum number of extra threads to have at any given time to evade deadlock,
* see [[scala.concurrent.BlockContext]].
*
* @return the global `ExecutionContext`
*/
def global: ExecutionContextExecutor = Implicits.global.asInstanceOf[ExecutionContextExecutor]
object Implicits {
/**
* The implicit global `ExecutionContext`. Import `global` when you want to provide the global
* `ExecutionContext` implicitly.
*
* The default `ExecutionContext` implementation is backed by a work-stealing thread pool. By default,
* the thread pool uses a target number of worker threads equal to the number of
* [[https://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#availableProcessors-- available processors]].
*/
implicit lazy val global: ExecutionContext = impl.ExecutionContextImpl.fromExecutor(null: Executor)
}
/** Creates an `ExecutionContext` from the given `ExecutorService`.
*
* @param e the `ExecutorService` to use. If `null`, a new `ExecutorService` is created with [[http://www.scala-lang.org/api/current/index.html#scala.concurrent.ExecutionContext$@global:scala.concurrent.ExecutionContextExecutor default configuration]].
* @param reporter a function for error reporting
* @return the `ExecutionContext` using the given `ExecutorService`
*/
def fromExecutorService(e: ExecutorService, reporter: Throwable => Unit): ExecutionContextExecutorService =
impl.ExecutionContextImpl.fromExecutorService(e, reporter)
/** Creates an `ExecutionContext` from the given `ExecutorService` with the [[scala.concurrent.ExecutionContext$.defaultReporter default reporter]].
*
* If it is guaranteed that none of the executed tasks are blocking, a single-threaded `ExecutorService`
* can be used to create an `ExecutionContext` as follows:
*
* {{{
* import java.util.concurrent.Executors
* val ec = ExecutionContext.fromExecutorService(Executors.newSingleThreadExecutor())
* }}}
*
* @param e the `ExecutorService` to use. If `null`, a new `ExecutorService` is created with [[http://www.scala-lang.org/api/current/index.html#scala.concurrent.ExecutionContext$@global:scala.concurrent.ExecutionContextExecutor default configuration]].
* @return the `ExecutionContext` using the given `ExecutorService`
*/
def fromExecutorService(e: ExecutorService): ExecutionContextExecutorService = fromExecutorService(e, defaultReporter)
/** Creates an `ExecutionContext` from the given `Executor`.
*
* @param e the `Executor` to use. If `null`, a new `Executor` is created with [[http://www.scala-lang.org/api/current/index.html#scala.concurrent.ExecutionContext$@global:scala.concurrent.ExecutionContextExecutor default configuration]].
* @param reporter a function for error reporting
* @return the `ExecutionContext` using the given `Executor`
*/
def fromExecutor(e: Executor, reporter: Throwable => Unit): ExecutionContextExecutor =
impl.ExecutionContextImpl.fromExecutor(e, reporter)
/** Creates an `ExecutionContext` from the given `Executor` with the [[scala.concurrent.ExecutionContext$.defaultReporter default reporter]].
*
* @param e the `Executor` to use. If `null`, a new `Executor` is created with [[http://www.scala-lang.org/api/current/index.html#scala.concurrent.ExecutionContext$@global:scala.concurrent.ExecutionContextExecutor default configuration]].
* @return the `ExecutionContext` using the given `Executor`
*/
def fromExecutor(e: Executor): ExecutionContextExecutor = fromExecutor(e, defaultReporter)
/** The default reporter simply prints the stack trace of the `Throwable` to [[http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#err System.err]].
*
* @return the function for error reporting
*/
def defaultReporter: Throwable => Unit = _.printStackTrace()
}
