/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.concurrent
import java.util.concurrent.{ ExecutorService, Executor }
import scala.annotation.implicitNotFound
import scala.util.Try
/**
* 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.
*
* It is possible to simply import
* `scala.concurrent.ExecutionContext.Implicits.global` to obtain an
* implicit `ExecutionContext`. This global context is a reasonable
* default thread pool.
*
* However, application developers should carefully consider where they
* want to set 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 might want to avoid
* hardcoding `scala.concurrent.ExecutionContext.Implicits.global` all
* over the place in your code.
* One approach is to add `(implicit ec: ExecutionContext)`
* to methods which need an `ExecutionContext`. Then import a specific
* context in one place for the entire application or module,
* passing it implicitly to individual methods.
*
* 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.
*
* `prepare` should be called at the site where an `ExecutionContext` is received (for
* example, through an implicit method parameter). The returned execution context may
* then be used to execute tasks. The role of `prepare` is to save any context relevant
* to an execution's ''call site'', so that this context may be restored at the
* ''execution site''. (These are often different: for example, execution may be
* suspended through a `Promise`'s future until the `Promise` is completed, which may
* be done in another thread, on another stack.)
*
* Note: a valid implementation of `prepare` is one that simply returns `this`.
*
* @return the prepared execution context
*/
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. 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]].
*
* @return the global `ExecutionContext`
*/
def global: ExecutionContextExecutor = Implicits.global
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: ExecutionContextExecutor = 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()
}
