edu.emory.mathcs.backport.java.util.concurrent
public class ExecutorCompletionService extends Object implements CompletionService
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); }
Constructor Summary | |
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ExecutorCompletionService(Executor executor)
Creates an ExecutorCompletionService using the supplied
executor for base task execution and a
LinkedBlockingQueue as a completion queue.
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ExecutorCompletionService(Executor executor, BlockingQueue completionQueue)
Creates an ExecutorCompletionService using the supplied
executor for base task execution and the supplied queue as its
completion queue.
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Method Summary | |
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Future | poll() |
Future | poll(long timeout, TimeUnit unit) |
Future | submit(Callable task) |
Future | submit(Runnable task, Object result) |
Future | take() |
Parameters: executor the executor to use
Throws: NullPointerException if executor is null
Parameters: executor the executor to use completionQueue 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 taskes cause them not to be retrievable.
Throws: NullPointerException if executor or completionQueue are null