Scala example source code file (ExecutionContext.scala)

This example Scala source code file (ExecutionContext.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

annotation, cannot, concurrent, executioncontext, executioncontextexecutor, executioncontextexecutorservice, executor, executorservice, implicits, throwable, unit, utilities, you

The ExecutionContext.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     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.
   */
  def execute(runnable: Runnable): Unit

  /** Reports that an asynchronous computation failed.
   */
  def reportFailure(@deprecatedName('t) cause: Throwable): Unit

  /** Prepares for the execution of a task. Returns the prepared
   *  execution context. A valid implementation of `prepare` is one
   *  that simply returns `this`.
   */
  def prepare(): ExecutionContext = this

}

/**
 * Union interface since Java does not support union types
 */
trait ExecutionContextExecutor extends ExecutionContext with Executor

/**
 * Union interface since Java does not support union types
 */
trait ExecutionContextExecutorService extends ExecutionContextExecutor with ExecutorService


/** Contains factory methods for creating execution contexts.
 */
object ExecutionContext {
  /**
   * This is the explicit global ExecutionContext,
   * call this when you want to provide the global ExecutionContext explicitly
   */
  def global: ExecutionContextExecutor = Implicits.global

  object Implicits {
    /**
     * This is the implicit global ExecutionContext,
     * import this when you want to provide the global ExecutionContext implicitly
     */
    implicit lazy val global: ExecutionContextExecutor = impl.ExecutionContextImpl.fromExecutor(null: Executor)
  }

  /** Creates an `ExecutionContext` from 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 default Reporter.
   */
  def fromExecutorService(e: ExecutorService): ExecutionContextExecutorService = fromExecutorService(e, defaultReporter)

  /** Creates an `ExecutionContext` from 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 default Reporter.
   */
  def fromExecutor(e: Executor): ExecutionContextExecutor = fromExecutor(e, defaultReporter)

  /** The default reporter simply prints the stack trace of the `Throwable` to System.err.
   */
  def defaultReporter: Throwable => Unit = _.printStackTrace()
}