ExecutorCompletionService (Java Platform SE 6) (original) (raw)

java.util.concurrent

Class ExecutorCompletionService

java.lang.Object extended by java.util.concurrent.ExecutorCompletionService

All Implemented Interfaces:

public class ExecutorCompletionService

A CompletionService that uses a supplied Executor to execute tasks. This class arranges that submitted tasks are, upon completion, placed on a queue accessible using take. The class is lightweight enough to be suitable for transient use when processing groups of tasks.

Usage Examples. Suppose you have a set of solvers for a certain problem, each returning a value of some type Result, and would like to run them concurrently, processing the results of each of them that return a non-null value, in some method use(Result r). You could write this as:

void solve(Executor e, Collection<Callable> solvers) throws InterruptedException, ExecutionException { CompletionService ecs = new ExecutorCompletionService(e); for (Callable s : solvers) ecs.submit(s); int n = solvers.size(); for (int i = 0; i < n; ++i) { Result r = ecs.take().get(); if (r != null) use(r); } }

Suppose instead that you would like to use the first non-null result of the set of tasks, ignoring any that encounter exceptions, and cancelling all other tasks when the first one is ready:

void solve(Executor e, Collection<Callable> solvers) throws InterruptedException { CompletionService ecs = new ExecutorCompletionService(e); int n = solvers.size(); List<Future> futures = new ArrayList<Future>(n); Result result = null; try { for (Callable s : solvers) futures.add(ecs.submit(s)); for (int i = 0; i < n; ++i) { try { Result r = ecs.take().get(); if (r != null) { result = r; break; } } catch (ExecutionException ignore) {} } } finally { for (Future f : futures) f.cancel(true); }

   if (result != null)
       use(result);

}

Constructor Summary
ExecutorCompletionService(Executor executor) Creates an ExecutorCompletionService using the supplied executor for base task execution and aLinkedBlockingQueue as a completion queue.
[ExecutorCompletionService](../../../java/util/concurrent/ExecutorCompletionService.html#ExecutorCompletionService%28java.util.concurrent.Executor, java.util.concurrent.BlockingQueue%29)(Executor executor,BlockingQueue<Future<V>> completionQueue) Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue.

Method Summary
Future<V>	poll() Retrieves and removes the Future representing the next completed task or null if none are present.
Future<V>	[poll](../../../java/util/concurrent/ExecutorCompletionService.html#poll%28long, java.util.concurrent.TimeUnit%29)(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](../../../java/util/concurrent/ExecutorCompletionService.html#submit%28java.lang.Runnable, V%29)(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.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, [wait](../../../java/lang/Object.html#wait%28long, int%29)

Constructor Detail

ExecutorCompletionService

public ExecutorCompletionService(Executor executor)

Creates an ExecutorCompletionService using the supplied executor for base task execution and aLinkedBlockingQueue as a completion queue.

Parameters:

executor - the executor to use

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if executor is null

ExecutorCompletionService

public ExecutorCompletionService(Executor executor, BlockingQueue<Future<V>> completionQueue)

Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue.

Parameters:

executor - the executor to use

completionQueue - the queue to use as the completion queue normally one dedicated for use by this service

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if executor or completionQueue are null

Method Detail

submit

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

Description copied from interface: [CompletionService](../../../java/util/concurrent/CompletionService.html#submit%28java.util.concurrent.Callable%29)

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.

Specified by:

[submit](../../../java/util/concurrent/CompletionService.html#submit%28java.util.concurrent.Callable%29) in interface [CompletionService](../../../java/util/concurrent/CompletionService.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/ExecutorCompletionService.html "type parameter in ExecutorCompletionService")>

Parameters:

task - the task to submit

Returns:

a Future representing pending completion of the task

submit

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

Description copied from interface: [CompletionService](../../../java/util/concurrent/CompletionService.html#submit%28java.lang.Runnable, V%29)

Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.

Specified by:

[submit](../../../java/util/concurrent/CompletionService.html#submit%28java.lang.Runnable, V%29) in interface [CompletionService](../../../java/util/concurrent/CompletionService.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/ExecutorCompletionService.html "type parameter in ExecutorCompletionService")>

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

take

public Future<V> take() throws InterruptedException

Description copied from interface: [CompletionService](../../../java/util/concurrent/CompletionService.html#take%28%29)

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

Specified by:

[take](../../../java/util/concurrent/CompletionService.html#take%28%29) in interface [CompletionService](../../../java/util/concurrent/CompletionService.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/ExecutorCompletionService.html "type parameter in ExecutorCompletionService")>

Returns:

the Future representing the next completed task

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

poll

public Future<V> poll()

Description copied from interface: [CompletionService](../../../java/util/concurrent/CompletionService.html#poll%28%29)

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

Specified by:

[poll](../../../java/util/concurrent/CompletionService.html#poll%28%29) in interface [CompletionService](../../../java/util/concurrent/CompletionService.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/ExecutorCompletionService.html "type parameter in ExecutorCompletionService")>

Returns:

the Future representing the next completed task, ornull if none are present

poll

public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException

Description copied from interface: [CompletionService](../../../java/util/concurrent/CompletionService.html#poll%28long, java.util.concurrent.TimeUnit%29)

Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.

Specified by:

[poll](../../../java/util/concurrent/CompletionService.html#poll%28long, java.util.concurrent.TimeUnit%29) in interface [CompletionService](../../../java/util/concurrent/CompletionService.html "interface in java.util.concurrent")<[V](../../../java/util/concurrent/ExecutorCompletionService.html "type parameter in ExecutorCompletionService")>

Parameters:

timeout - how long to wait before giving up, in units ofunit

unit - a TimeUnit determining how to interpret thetimeout parameter

Returns:

the Future representing the next completed task ornull 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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For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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