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/*
 * 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;

/**
 * A service that decouples the production of new asynchronous tasks
 * from the consumption of the results of completed tasks.  Producers
 * submit tasks for execution. Consumers take
 * completed tasks and process their results in the order they
 * complete.  A CompletionService can for example be used to
 * manage asynchronous IO, in which tasks that perform reads are
 * submitted in one part of a program or system, and then acted upon
 * in a different part of the program when the reads complete,
 * possibly in a different order than they were requested.
 *
 * 

Typically, a CompletionService relies on a separate * {@link Executor} to actually execute the tasks, in which case the * CompletionService only manages an internal completion * queue. The {@link ExecutorCompletionService} class provides an * implementation of this approach. * *

Memory consistency effects: Actions in a thread prior to * submitting a task to a {@code CompletionService} * happen-before * actions taken by that task, which in turn happen-before * actions following a successful return from the corresponding {@code take()}. * */ public interface CompletionService { /** * Submits a value-returning task for execution and returns a Future * representing the pending results of the task. Upon completion, * this task may be taken or polled. * * @param task the task to submit * @return a Future representing pending completion of the task * @throws RejectedExecutionException if the task cannot be * scheduled for execution * @throws NullPointerException if the task is null */ Future submit(Callable task); /** * Submits a Runnable task for execution and returns a Future * representing that task. Upon completion, this task may be * taken or polled. * * @param task the task to submit * @param result the result to return upon successful completion * @return a Future representing pending completion of the task, * and whose get() method will return the given * result value upon completion * @throws RejectedExecutionException if the task cannot be * scheduled for execution * @throws NullPointerException if the task is null */ Future submit(Runnable task, Object result); /** * Retrieves and removes the Future representing the next * completed task, waiting if none are yet present. * * @return the Future representing the next completed task * @throws InterruptedException if interrupted while waiting */ Future take() throws InterruptedException; /** * Retrieves and removes the Future representing the next * completed task or null if none are present. * * @return the Future representing the next completed task, or * null if none are present */ Future poll(); /** * Retrieves and removes the Future representing the next * completed task, waiting if necessary up to the specified wait * time if none are yet present. * * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * @return the Future representing the next completed task or * null if the specified waiting time elapses * before one is present * @throws InterruptedException if interrupted while waiting */ Future poll(long timeout, TimeUnit unit) throws InterruptedException; }





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