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/* |
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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/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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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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/** |
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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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/** |
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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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/** |
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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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/** |
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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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} |
