added in API level 1

CompletionService

public interface CompletionService

java.util.concurrent.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 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 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().

Summary

Public methods

abstract 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.

abstract Future<V> poll()

Retrieves and removes the Future representing the next completed task, or null if none are present.

abstract Future<V> submit(Runnable task, V result)

Submits a Runnable task for execution and returns a Future representing that task.

abstract Future<V> submit(Callable<V> task)

Submits a value-returning task for execution and returns a Future representing the pending results of the task.

abstract Future<V> take()

Retrieves and removes the Future representing the next completed task, waiting if none are yet present.

Public methods

poll

added in API level 1
public abstract 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.

Parameters
timeout long: how long to wait before giving up, in units of unit

unit TimeUnit: a TimeUnit determining how to interpret the timeout parameter

Returns
Future<V> 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

poll

added in API level 1
public abstract Future<V> poll ()

Retrieves and removes the Future representing the next completed task, or null if none are present.

Returns
Future<V> the Future representing the next completed task, or null if none are present

submit

added in API level 1
public abstract 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 Runnable: the task to submit

result V: the result to return upon successful completion

Returns
Future<V> 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

submit

added in API level 1
public abstract 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 Callable: the task to submit

Returns
Future<V> a Future representing pending completion of the task

Throws
RejectedExecutionException if the task cannot be scheduled for execution
NullPointerException if the task is null

take

added in API level 1
public abstract Future<V> take ()

Retrieves and removes the Future representing the next completed task, waiting if none are yet present.

Returns
Future<V> the Future representing the next completed task

Throws
InterruptedException if interrupted while waiting