Module java.base
Package java.util.concurrent

Interface CompletionService<V>

  • 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 I/O, 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().

    Since:
    1.5

    • Method Summary

      Modifier and Type Method 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​(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.
      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