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jeremybenn |
/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/licenses/publicdomain
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*/
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package java.util.concurrent;
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/**
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* A service that decouples the production of new asynchronous tasks
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* from the consumption of the results of completed tasks. Producers
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* <tt>submit</tt> tasks for execution. Consumers <tt>take</tt>
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* completed tasks and process their results in the order they
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* complete. A <tt>CompletionService</tt> can for example be used to
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* manage asynchronous IO, in which tasks that perform reads are
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* submitted in one part of a program or system, and then acted upon
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* in a different part of the program when the reads complete,
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* possibly in a different order than they were requested.
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*
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* <p>Typically, a <tt>CompletionService</tt> relies on a separate
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* {@link Executor} to actually execute the tasks, in which case the
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* <tt>CompletionService</tt> only manages an internal completion
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* queue. The {@link ExecutorCompletionService} class provides an
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* implementation of this approach.
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*
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* <p>Memory consistency effects: Actions in a thread prior to
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* submitting a task to a {@code CompletionService}
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* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
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* actions taken by that task, which in turn <i>happen-before</i>
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* actions following a successful return from the corresponding {@code take()}.
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*
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*/
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public interface CompletionService<V> {
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/**
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* Submits a value-returning task for execution and returns a Future
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* representing the pending results of the task. Upon completion,
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* this task may be taken or polled.
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*
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* @param task the task to submit
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* @return a Future representing pending completion of the task
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if the task is null
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*/
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Future<V> submit(Callable<V> task);
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/**
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* Submits a Runnable task for execution and returns a Future
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* representing that task. Upon completion, this task may be
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* taken or polled.
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*
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* @param task the task to submit
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* @param result the result to return upon successful completion
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* @return a Future representing pending completion of the task,
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* and whose <tt>get()</tt> method will return the given
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* result value upon completion
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* @throws RejectedExecutionException if the task cannot be
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* scheduled for execution
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* @throws NullPointerException if the task is null
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*/
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Future<V> submit(Runnable task, V result);
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/**
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* Retrieves and removes the Future representing the next
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* completed task, waiting if none are yet present.
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*
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* @return the Future representing the next completed task
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* @throws InterruptedException if interrupted while waiting
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*/
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Future<V> take() throws InterruptedException;
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/**
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* Retrieves and removes the Future representing the next
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* completed task or <tt>null</tt> if none are present.
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*
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* @return the Future representing the next completed task, or
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* <tt>null</tt> if none are present
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*/
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Future<V> poll();
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/**
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* Retrieves and removes the Future representing the next
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* completed task, waiting if necessary up to the specified wait
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* time if none are yet present.
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*
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* @param timeout how long to wait before giving up, in units of
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* <tt>unit</tt>
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the
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* <tt>timeout</tt> parameter
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* @return the Future representing the next completed task or
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* <tt>null</tt> if the specified waiting time elapses
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* before one is present
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* @throws InterruptedException if interrupted while waiting
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*/
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Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
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}
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