File Doc Category Size Date Package
CompletionService.java API Doc Java SE 6 API 4012 Tue Jun 10 00:25:56 BST 2008 java.util.concurrent

CompletionService

public interface CompletionService

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()}.

Fields Summary
Constructors Summary
Methods Summary
public java.util.concurrent.Future poll()
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
public java.util.concurrent.Future poll(long timeout, java.util.concurrent.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.
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
public java.util.concurrent.Future submit(java.util.concurrent.Callable 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.
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
public java.util.concurrent.Future submit(java.lang.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.
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
public java.util.concurrent.Future take()
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