Play Framework/Scala example source code file (Execution.scala)

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

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

Play Framework tags/keywords

api, arraydeque, concurrent, execution, executioncontext, implicits, iterate, library, play, play framework, runnable, threadlocal, throwable, unit

The Execution.scala Play Framework example source code

/*
 * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
 */
package play.api.libs.iteratee

import java.util.{ ArrayDeque, Deque }
import scala.annotation.tailrec
import scala.concurrent.ExecutionContext

/**
 * Contains the default ExecutionContext used by Iteratees.
 */
object Execution {

  def defaultExecutionContext: ExecutionContext = Implicits.defaultExecutionContext

  object Implicits {
    implicit def defaultExecutionContext: ExecutionContext = Execution.trampoline
    implicit def trampoline: ExecutionContext = Execution.trampoline
  }

  /**
   * Executes in the current thread. Uses a thread local trampoline to make sure the stack
   * doesn't overflow. Since this ExecutionContext executes on the current thread, it should
   * only be used to run small bits of fast-running code. We use it here to run the internal
   * iteratee code.
   *
   * Blocking should be strictly avoided as it could hog the current thread.
   * Also, since we're running on a single thread, blocking code risks deadlock.
   */
  object trampoline extends ExecutionContext {

    private val local = new ThreadLocal[Deque[Runnable]]

    def execute(runnable: Runnable): Unit = {
      @volatile var queue = local.get()
      if (queue == null) {
        // Since there is no local queue, we need to install one and
        // start our trampolining loop.
        try {
          queue = new ArrayDeque(4)
          queue.addLast(runnable)
          local.set(queue)
          while (!queue.isEmpty) {
            val runnable = queue.removeFirst()
            runnable.run()
          }
        } finally {
          // We've emptied the queue, so tidy up.
          local.set(null)
        }
      } else {
        // There's already a local queue that is being executed.
        // Just stick our runnable on the end of that queue.
        queue.addLast(runnable)
      }
    }

    def reportFailure(t: Throwable): Unit = t.printStackTrace()
  }

}