CompletionService (Java Platform SE 7 b138)

All Known Implementing Classes:

ExecutorCompletionService
```
public interface CompletionService<V>
```
A service that decouples the production of new asynchronous tasks from the consumption of the results of completed tasks. Producers submit tasks for execution. Consumers take completed tasks and process their results in the order they complete. A CompletionService can for example be used to manage asynchronous IO, in which tasks that perform reads are submitted in one part of a program or system, and then acted upon in a different part of the program when the reads complete, possibly in a different order than they were requested.
Typically, a CompletionService relies on a separate Executor to actually execute the tasks, in which case the CompletionService only manages an internal completion queue. The ExecutorCompletionService class provides an implementation of this approach.
Memory consistency effects: Actions in a thread prior to submitting a task to a CompletionService happen-before actions taken by that task, which in turn happen-before actions following a successful return from the corresponding take().

Method Summary

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.

- Method Detail
  - submit
```
Future<V> submit(Callable<V> task)
```
    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.
    
    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
  - submit
```
Future<V> submit(Runnable task,
               V result)
```
    Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.
    
    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
  - take
```
Future<V> take()
               throws InterruptedException
```
    Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
    
    Returns:
    the Future representing the next completed task
    
    Throws:
    
    InterruptedException - if interrupted while waiting
  - poll
```
Future<V> poll()
```
    Retrieves and removes the Future representing the next completed task or null if none are present.
    
    Returns:
    the Future representing the next completed task, or null if none are present
  - poll
```
Future<V> poll(long timeout,
             TimeUnit unit)
               throws InterruptedException
```
    Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
    
    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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DRAFT ea-b138

Interface CompletionService<V>

Method Summary

Method Detail

submit

submit

take

poll

poll