- java.lang.Object
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- java.util.concurrent.ExecutorCompletionService<V>
 
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- All Implemented Interfaces:
- CompletionService<V>
 
 public class ExecutorCompletionService<V> extends Object implements CompletionService<V> ACompletionServicethat uses a suppliedExecutorto execute tasks. This class arranges that submitted tasks are, upon completion, placed on a queue accessible usingtake. 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 methoduse(Result r). You could write this as:
 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, 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); } }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); }- Since:
- 1.5
 
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Constructor SummaryConstructors Constructor Description ExecutorCompletionService(Executor executor)Creates an ExecutorCompletionService using the supplied executor for base task execution and aLinkedBlockingQueueas 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.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description Future<V>submit(Runnable task, V result)Submits a Runnable task for execution and returns a Future representing that task.Future<V>submit(Callable<V> task)Submits a value-returning task for execution and returns a Future representing the pending results of the task.- 
Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Methods declared in interface java.util.concurrent.CompletionServicepoll, poll, take
 
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Constructor Detail- 
ExecutorCompletionServicepublic ExecutorCompletionService(Executor executor) Creates an ExecutorCompletionService using the supplied executor for base task execution and aLinkedBlockingQueueas a completion queue.- Parameters:
- executor- the executor to use
- Throws:
- NullPointerException- if executor is- null
 
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ExecutorCompletionServicepublic 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.- 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.addoperations for completed tasks cause them not to be retrievable.
- Throws:
- NullPointerException- if executor or completionQueue are- null
 
 
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Method Detail- 
submitpublic Future<V> submit(Callable<V> task) Description copied from interface:CompletionServiceSubmits a value-returning task for execution and returns a Future representing the pending results of the task. Upon completion, this task may be taken or polled.- Specified by:
- submitin interface- CompletionService<V>
- Parameters:
- task- the task to submit
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
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submitpublic Future<V> submit(Runnable task, V result) Description copied from interface:CompletionServiceSubmits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.- Specified by:
- submitin interface- CompletionService<V>
- Parameters:
- task- the task to submit
- result- the result to return upon successful completion
- Returns:
- a Future representing pending completion of the task,
         and whose get()method will return the given result value upon completion
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
 
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