| 9 |
|
|
| 10 |
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/** |
| 11 |
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* A {@link CompletionService} that uses a supplied {@link Executor} |
| 12 |
< |
* to execute tasks. |
| 12 |
> |
* to execute tasks. An <tt>ExecutorCompletionService</tt> can be |
| 13 |
> |
* useful as an add-on to solve task coordination problems. |
| 14 |
> |
* |
| 15 |
> |
* <p> |
| 16 |
> |
* |
| 17 |
> |
* <b>Usage Examples.</b> |
| 18 |
> |
* Suppose you have a set of solvers for a certain problem, |
| 19 |
> |
* and would like to run them concurrently, using the results of each of them |
| 20 |
> |
* that return a non-null value. You could write this as: |
| 21 |
> |
* |
| 22 |
> |
* <pre> |
| 23 |
> |
* void solve(Executor e, Collection<Callable<Result>> solvers) |
| 24 |
> |
* throws InterruptedException, ExecutionException { |
| 25 |
> |
* ExecutorCompletionService<Result> ecs = new |
| 26 |
> |
* ExecutorCompletionService<Result>(e); |
| 27 |
> |
* for (Callable<Result> s : solvers) |
| 28 |
> |
* ecs.submit(s); |
| 29 |
> |
* int n = solvers.size(); |
| 30 |
> |
* for (int i = 0; i < n; ++i) { |
| 31 |
> |
* Result r = ecs.take().get(); |
| 32 |
> |
* if (r != null) |
| 33 |
> |
* use(r); |
| 34 |
> |
* } |
| 35 |
> |
* } |
| 36 |
> |
* </pre> |
| 37 |
> |
* |
| 38 |
> |
* Suppose instead that you would like to use the first non-null result |
| 39 |
> |
* of a set of tasks, ignoring any of those that encounter exceptions |
| 40 |
> |
* and cancelling all of the other tasks when the first one is ready: |
| 41 |
> |
* |
| 42 |
> |
* <pre> |
| 43 |
> |
* void solve(Executor e, Collection<Callable<Result>> solvers) |
| 44 |
> |
* throws InterruptedException { |
| 45 |
> |
* ExecutorCompletionService<Result> ecs = |
| 46 |
> |
* new ExecutorCompletionService<Result>(e); |
| 47 |
> |
* int n = solvers.size(); |
| 48 |
> |
* ArrayList<Future<Result>> futures = |
| 49 |
> |
* new ArrayList<Future<Result>>(n); |
| 50 |
> |
* Result result = null; |
| 51 |
> |
* try { |
| 52 |
> |
* for (Callable<Result> s : solvers) |
| 53 |
> |
* futures.add(ecs.submit(s)); |
| 54 |
> |
* for (int i = 0; i < n; ++i) { |
| 55 |
> |
* try { |
| 56 |
> |
* Result r = ecs.take().get(); |
| 57 |
> |
* if (r != null) { |
| 58 |
> |
* result = r; |
| 59 |
> |
* break; |
| 60 |
> |
* } |
| 61 |
> |
* } catch(ExecutionException ignore) {} |
| 62 |
> |
* } |
| 63 |
> |
* } |
| 64 |
> |
* finally { |
| 65 |
> |
* for (Future<Result> f : futures) |
| 66 |
> |
* f.cancel(true); |
| 67 |
> |
* } |
| 68 |
> |
* |
| 69 |
> |
* if (result != null) |
| 70 |
> |
* use(result); |
| 71 |
> |
* } |
| 72 |
> |
* </pre> |
| 73 |
|
*/ |
| 74 |
|
public class ExecutorCompletionService<V> implements CompletionService<V> { |
| 75 |
|
private final Executor executor; |
| 88 |
|
* Creates an ExecutorCompletionService using the supplied |
| 89 |
|
* executor for base task execution and a |
| 90 |
|
* {@link LinkedBlockingQueue} as a completion queue. |
| 91 |
< |
* @param executor the executor to use; normally |
| 32 |
< |
* one dedicated for use by this service |
| 91 |
> |
* @param executor the executor to use |
| 92 |
|
8 @throws NullPointerException if executor is <tt>null</tt> |
| 93 |
|
*/ |
| 94 |
|
public ExecutorCompletionService(Executor executor) { |
| 102 |
|
* Creates an ExecutorCompletionService using the supplied |
| 103 |
|
* executor for base task execution and the supplied queue as its |
| 104 |
|
* completion queue. |
| 105 |
< |
* @param executor the executor to use; normally |
| 47 |
< |
* one dedicated for use by this service |
| 105 |
> |
* @param executor the executor to use |
| 106 |
|
* @param completionQueue the queue to use as the completion queue; |
| 107 |
|
* normally one dedicated for use by this service |
| 108 |
|
8 @throws NullPointerException if executor or completionQueue are <tt>null</tt> |
| 138 |
|
public Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException { |
| 139 |
|
return completionQueue.poll(timeout, unit); |
| 140 |
|
} |
| 141 |
+ |
|
| 142 |
|
} |
| 143 |
|
|
| 144 |
|
|
