java.util.concurrent.ExecutorCompletionService<V>
is new.
java.lang.Object
public class ExecutorCompletionService<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 catch(ExecutionException ignore) {}
}
}
finally {
for (Future<Result> 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 a LinkedBlockingQueue as a completion queue. |
|
|
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. |
|
| Method Summary | |
|---|---|
| Future < V > |
poll
() Retrieves and removes the Future representing the next completed task or null if none are present. |
| 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. |
| 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
(
Runnable
task,
V
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 |
| Constructor Detail |
|---|
public ExecutorCompletionService(Executor executor)
public ExecutorCompletionService(Executor executor,
BlockingQueue<Future<V>> completionQueue)
| Method Detail |
|---|
public Future<V> submit(Callable<V> task)
public Future<V> submit(Runnable task,
V result)
task. Upon
public Future<V> take()
throws InterruptedException
waiting
public Future<V> poll()
present
public Future<V> poll(long timeout,
TimeUnit unit)
throws InterruptedException
present
waiting