Java compact1, compact2, compact3 java.util.concurrent Class ExecutorCompletionService<V>（JDK8）

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Standard Ed. 8

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java.lang.Object
- java.util.concurrent.ExecutorCompletionService<V>

All Implemented Interfaces:: CompletionService<V>

public class ExecutorCompletionService<V>
extends Object
implements CompletionService<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 ignore) {}
         }
     }
     finally {
         for (Future<Result> f : futures)
             f.cancel(true);
     }

     if (result != null)
         use(result);
 }

Constructor Summary

Constructors
Constructor and Description
`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

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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 result)` 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
  - ExecutorCompletionService
```
public ExecutorCompletionService(Executor executor)
```
    Creates an ExecutorCompletionService using the supplied executor for base task execution and a LinkedBlockingQueue as a completion queue.
    
    Parameters:
    
    executor - the executor to use
    
    Throws:
    
    NullPointerException - if executor is null
  - ExecutorCompletionService
```
public 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.add operations for completed tasks cause them not to be retrievable.
    
    Throws:
    
    NullPointerException - if executor or completionQueue are null
- Method Detail
  - submit
```
public Future<V> submit(Callable<V> task)
```
    Description copied from interface: CompletionService
    
    Submits 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:
    
    submit in interface CompletionService<V>
    
    Parameters:
    
    task - the task to submit
    
    Returns:
    
    a Future representing pending completion of the task
  - submit
```
public Future<V> submit(Runnable task,
                        V result)
```
    Description copied from interface: CompletionService
    
    Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.
    
    Specified by:
    
    submit in 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
  - take
```
public Future<V> take()
               throws InterruptedException
```
    Description copied from interface: CompletionService
    
    Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
    
    Specified by:
    
    take in interface CompletionService<V>
    
    Returns:
    
    the Future representing the next completed task
    
    Throws:
    
    InterruptedException - if interrupted while waiting
  - poll
```
public Future<V> poll()
```
    Description copied from interface: CompletionService
    
    Retrieves and removes the Future representing the next completed task, or null if none are present.
    
    Specified by:
    
    poll in interface CompletionService<V>
    
    Returns:
    
    the Future representing the next completed task, or null if none are present
  - poll
```
public Future<V> poll(long timeout,
                      TimeUnit unit)
               throws InterruptedException
```
    Description copied from interface: CompletionService
    
    Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
    
    Specified by:
    
    poll in interface CompletionService<V>
    
    Parameters:
    
    timeout - how long to wait before giving up, in units of unit
    
    unit - a TimeUnit determining how to interpret the timeout parameter
    
    Returns:
    
    the Future representing the next completed task or null if the specified waiting time elapses before one is present
    
    Throws:
    
    InterruptedException - if interrupted while waiting

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Java™ Platform
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Detail:
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Java compact1, compact2, compact3 java.util.concurrent Class ExecutorCompletionService<V>（JDK8）

Class ExecutorCompletionService<V>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

ExecutorCompletionService

ExecutorCompletionService

Method Detail

submit

submit

take

poll

poll