public class ExecutorCompletionService<V> extends Object implements CompletionService<V>
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<Result>> solvers)
throws InterruptedException, ExecutionException {
CompletionService<Result> ecs
= new ExecutorCompletionService<Result>(e);
for (Callable<Result> 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<Result>> solvers)
throws InterruptedException {
CompletionService<Result> ecs
= new ExecutorCompletionService<Result>(e);
int n = solvers.size();
List<Future<Result>> futures
= new ArrayList<Future<Result>>(n);
Result result = null;
try {
for (Callable<Result> 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<Result> f : futures)
f.cancel(true);
}
if (result != null)
use(result);
}
public ExecutorCompletionService(Executor executor)
Creates an ExecutorCompletionService using the supplied executor for base task execution and a LinkedBlockingQueue as a completion queue.
executor - the executor to useNullPointerException - if executor is null
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.
executor - the executor to usecompletionQueue - the queue to use as the completion queue normally one dedicated for use by this service. This queue is treated as unbounded -- failed attempted Queue.add operations for completed tasks cause them not to be retrievable.NullPointerException - if executor or completionQueue are null
public Future<V> submit(Callable<V> task)
Description copied from interface: CompletionService
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.
submit in interface CompletionService<V>
task - the task to submitpublic Future<V> submit(Runnable task,
V result) Description copied from interface: CompletionService
Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.
submit in interface CompletionService<V>
task - the task to submitresult - the result to return upon successful completionget() method will return the given result value upon completionpublic Future<V> take()
throws InterruptedException Description copied from interface: CompletionService
Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
take in interface CompletionService<V>
InterruptedException - if interrupted while waitingpublic Future<V> poll()
Description copied from interface: CompletionService
Retrieves and removes the Future representing the next completed task, or null if none are present.
poll in interface CompletionService<V>
null if none are presentpublic Future<V> poll(long timeout,
TimeUnit unit)
throws InterruptedException Description copied from interface: CompletionService
Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
poll in interface CompletionService<V>
timeout - how long to wait before giving up, in units of unit
unit - a TimeUnit determining how to interpret the timeout parameternull if the specified waiting time elapses before one is presentInterruptedException - if interrupted while waiting
© 1993–2017, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.