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/** |
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* A {@link CompletionService} that uses a supplied {@link Executor} |
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* to execute tasks. This class arranges that submitted tasks are, |
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* upon completion, placed on a queue accessible using <tt>take</tt>. |
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* upon completion, placed on a queue accessible using {@code take}. |
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* The class is lightweight enough to be suitable for transient use |
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* when processing groups of tasks. |
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* |
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* <b>Usage Examples.</b> |
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* |
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* Suppose you have a set of solvers for a certain problem, each |
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* returning a value of some type <tt>Result</tt>, and would like to |
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* returning a value of some type {@code Result}, and would like to |
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* run them concurrently, processing the results of each of them that |
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* return a non-null value, in some method <tt>use(Result r)</tt>. You |
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* return a non-null value, in some method {@code use(Result r)}. You |
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* could write this as: |
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* |
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* <pre> |
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* void solve(Executor e, |
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* Collection<Callable<Result>> solvers) |
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* <pre> {@code |
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* void solve(Executor e, |
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* Collection<Callable<Result>> solvers) |
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* throws InterruptedException, ExecutionException { |
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* CompletionService<Result> ecs |
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* = new ExecutorCompletionService<Result>(e); |
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* for (Callable<Result> s : solvers) |
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* ecs.submit(s); |
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* int n = solvers.size(); |
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* for (int i = 0; i < n; ++i) { |
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* Result r = ecs.take().get(); |
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* if (r != null) |
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* use(r); |
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* } |
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< |
* } |
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* </pre> |
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* CompletionService<Result> ecs |
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* = new ExecutorCompletionService<Result>(e); |
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* for (Callable<Result> s : solvers) |
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* ecs.submit(s); |
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> |
* int n = solvers.size(); |
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> |
* for (int i = 0; i < n; ++i) { |
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> |
* Result r = ecs.take().get(); |
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> |
* if (r != null) |
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> |
* use(r); |
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> |
* } |
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> |
* }}</pre> |
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* |
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* Suppose instead that you would like to use the first non-null result |
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* of the set of tasks, ignoring any that encounter exceptions, |
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* and cancelling all other tasks when the first one is ready: |
| 45 |
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* |
| 46 |
< |
* <pre> |
| 47 |
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* void solve(Executor e, |
| 48 |
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* Collection<Callable<Result>> solvers) |
| 46 |
> |
* <pre> {@code |
| 47 |
> |
* void solve(Executor e, |
| 48 |
> |
* Collection<Callable<Result>> solvers) |
| 49 |
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* throws InterruptedException { |
| 50 |
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* CompletionService<Result> ecs |
| 51 |
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* = new ExecutorCompletionService<Result>(e); |
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* int n = solvers.size(); |
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* List<Future<Result>> futures |
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* = new ArrayList<Future<Result>>(n); |
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* Result result = null; |
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* try { |
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* for (Callable<Result> s : solvers) |
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* futures.add(ecs.submit(s)); |
| 59 |
< |
* for (int i = 0; i < n; ++i) { |
| 60 |
< |
* try { |
| 61 |
< |
* Result r = ecs.take().get(); |
| 62 |
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* if (r != null) { |
| 63 |
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* result = r; |
| 64 |
< |
* break; |
| 65 |
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* } |
| 66 |
< |
* } catch (ExecutionException ignore) {} |
| 67 |
< |
* } |
| 68 |
< |
* } |
| 69 |
< |
* finally { |
| 70 |
< |
* for (Future<Result> f : futures) |
| 71 |
< |
* f.cancel(true); |
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< |
* } |
| 73 |
< |
* |
| 74 |
< |
* if (result != null) |
| 75 |
< |
* use(result); |
| 76 |
< |
* } |
| 78 |
< |
* </pre> |
| 50 |
> |
* CompletionService<Result> ecs |
| 51 |
> |
* = new ExecutorCompletionService<Result>(e); |
| 52 |
> |
* int n = solvers.size(); |
| 53 |
> |
* List<Future<Result>> futures |
| 54 |
> |
* = new ArrayList<Future<Result>>(n); |
| 55 |
> |
* Result result = null; |
| 56 |
> |
* try { |
| 57 |
> |
* for (Callable<Result> s : solvers) |
| 58 |
> |
* futures.add(ecs.submit(s)); |
| 59 |
> |
* for (int i = 0; i < n; ++i) { |
| 60 |
> |
* try { |
| 61 |
> |
* Result r = ecs.take().get(); |
| 62 |
> |
* if (r != null) { |
| 63 |
> |
* result = r; |
| 64 |
> |
* break; |
| 65 |
> |
* } |
| 66 |
> |
* } catch (ExecutionException ignore) {} |
| 67 |
> |
* } |
| 68 |
> |
* } |
| 69 |
> |
* finally { |
| 70 |
> |
* for (Future<Result> f : futures) |
| 71 |
> |
* f.cancel(true); |
| 72 |
> |
* } |
| 73 |
> |
* |
| 74 |
> |
* if (result != null) |
| 75 |
> |
* use(result); |
| 76 |
> |
* }}</pre> |
| 77 |
|
*/ |
| 78 |
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public class ExecutorCompletionService<V> implements CompletionService<V> { |
| 79 |
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private final Executor executor; |
| 112 |
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* {@link LinkedBlockingQueue} as a completion queue. |
| 113 |
|
* |
| 114 |
|
* @param executor the executor to use |
| 115 |
< |
* @throws NullPointerException if executor is <tt>null</tt> |
| 115 |
> |
* @throws NullPointerException if executor is {@code null} |
| 116 |
|
*/ |
| 117 |
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public ExecutorCompletionService(Executor executor) { |
| 118 |
|
if (executor == null) |
| 130 |
|
* |
| 131 |
|
* @param executor the executor to use |
| 132 |
|
* @param completionQueue the queue to use as the completion queue |
| 133 |
< |
* normally one dedicated for use by this service. This queue is |
| 134 |
< |
* treated as unbounded -- failed attempted <tt>Queue.add</tt> |
| 135 |
< |
* operations for completed taskes cause them not to be |
| 136 |
< |
* retrievable. |
| 137 |
< |
* @throws NullPointerException if executor or completionQueue are <tt>null</tt> |
| 133 |
> |
* normally one dedicated for use by this service. This |
| 134 |
> |
* queue is treated as unbounded -- failed attempted |
| 135 |
> |
* {@code Queue.add} operations for completed taskes cause |
| 136 |
> |
* them not to be retrievable. |
| 137 |
> |
* @throws NullPointerException if executor or completionQueue are {@code null} |
| 138 |
|
*/ |
| 139 |
|
public ExecutorCompletionService(Executor executor, |
| 140 |
|
BlockingQueue<Future<V>> completionQueue) { |
