Java™ Platform
Standard Ed. 6

java.util.concurrent
Interface CompletionService<V>

All Known Implementing Classes:
ExecutorCompletionService

public interface CompletionService<V>

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 Executor to actually execute the tasks, in which case the CompletionService only manages an internal completion queue. The ExecutorCompletionService class provides an implementation of this approach.

Memory consistency effects: Actions in a thread prior to submitting a task to a CompletionService happen-before actions taken by that task, which in turn happen-before actions following a successful return from the corresponding take().


Method Summary
 Future<V> poll()
          Retrieves and removes the Future representing the next completed task or null if none are present.
 Future<V> poll(long timeout, TimeUnit unit)
          Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
 Future<V> submit(Callable<V> task)
          Submits a value-returning task for execution and returns a Future representing the pending results of the task.
 Future<V> submit(Runnable task, V result)
          Submits a Runnable task for execution and returns a Future representing that task.
 Future<V> take()
          Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
 

Method Detail

submit

Future<V> submit(Callable<V> task)
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.

Parameters:
task - the task to submit
Returns:
a Future representing pending completion of the task
Throws:
RejectedExecutionException - if the task cannot be scheduled for execution
NullPointerException - if the task is null

submit

Future<V> submit(Runnable task,
                 V result)
Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.

Parameters:
task - the task to submit
result - the result to return upon successful completion
Returns:
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
NullPointerException - if the task is null

take

Future<V> take()
               throws InterruptedException
Retrieves and removes the Future representing the next completed task, waiting if none are yet present.

Returns:
the Future representing the next completed task
Throws:
InterruptedException - if interrupted while waiting

poll

Future<V> poll()
Retrieves and removes the Future representing the next completed task or null if none are present.

Returns:
the Future representing the next completed task, or null if none are present

poll

Future<V> poll(long timeout,
               TimeUnit unit)
               throws InterruptedException
Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.

Parameters:
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameter
Returns:
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

Java™ Platform
Standard Ed. 6

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