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FlexDoc/Javadoc 2.0 Demo Java Doc |
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> cs
= new ExecutorCompletionService<>(e);
solvers.forEach(cs::submit);
for (int i = solvers.size(); i > 0; i--) {
Result r = cs.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> cs
= new ExecutorCompletionService<>(e);
int n = solvers.size();
List<Future<Result>> futures = new ArrayList<>(n);
Result result = null;
try {
solvers.forEach(solver -> futures.add(cs.submit(solver)));
for (int i = n; i > 0; i--) {
try {
Result r = cs.take().get();
if (r != null) {
result = r;
break;
}
} catch (ExecutionException ignore) {}
}
} finally {
futures.forEach(future -> future.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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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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poll()
Retrieves and removes the Future representing the next
completed task, or null if none are present.
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Retrieves and removes the Future representing the next
completed task, waiting if necessary up to the specified wait
time if none are yet present.
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Submits a value-returning task for execution and returns a Future
representing the pending results of the task.
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Submits a Runnable task for execution and returns a Future
representing that task.
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take()
Retrieves and removes the Future representing the next
completed task, waiting if none are yet present.
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Methods inherited from class java.lang.Object |
public ExecutorCompletionService |
(Executor executor) |
public ExecutorCompletionService |
() |
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throws |
() |
(long timeout, TimeUnit unit) |
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throws |
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FlexDoc/Javadoc 2.0 Demo Java Doc |