CompletionService (Java Platform SE 8 ) (original) (raw)

• All Known Implementing Classes:
  ExecutorCompletionService

public interface CompletionService
A service that decouples the production of new asynchronous tasks from the consumption of the results of completed tasks. Producerssubmit 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 I/O, 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 separateExecutor to actually execute the tasks, in which case theCompletionService 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

  All Methods Instance Methods Abstract Methods

  Modifier and Type	Method	Description
  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](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> submit([Callable](../../../java/util/concurrent/Callable.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> 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](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
     `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
     * #### submit  
     [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> submit([Runnable](../../../java/lang/Runnable.html "interface in java.lang") task,  
                      [V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService") 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](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent")` \- if the task cannot be scheduled for execution  
     `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if the task is null  
     * #### take  
     [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> take()  
             throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")  
     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](../../../java/lang/InterruptedException.html "class in java.lang")` \- if interrupted while waiting  
     * #### poll  
     [Future](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> 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](../../../java/util/concurrent/Future.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/CompletionService.html "type parameter in CompletionService")> poll(long timeout,  
                    [TimeUnit](../../../java/util/concurrent/TimeUnit.html "enum in java.util.concurrent") unit)  
             throws [InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang")  
     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](../../../java/lang/InterruptedException.html "class in java.lang")` \- if interrupted while waiting

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