| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| /** |
| * A service that decouples the production of new asynchronous tasks |
| * from the consumption of the results of completed tasks. Producers |
| * <tt>submit</tt> tasks for execution. Consumers <tt>take</tt> |
| * completed tasks and process their results in the order they |
| * complete. A <tt>CompletionService</tt> 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. |
| * |
| * <p>Typically, a <tt>CompletionService</tt> relies on a separate |
| * {@link Executor} to actually execute the tasks, in which case the |
| * <tt>CompletionService</tt> only manages an internal completion |
| * queue. The {@link ExecutorCompletionService} class provides an |
| * implementation of this approach. |
| * |
| * <p>Memory consistency effects: Actions in a thread prior to |
| * submitting a task to a {@code CompletionService} |
| * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
| * actions taken by that task, which in turn <i>happen-before</i> |
| * actions following a successful return from the corresponding {@code take()}. |
| * |
| */ |
| public interface CompletionService<V> { |
| /** |
| * 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. |
| * |
| * @param task the task to submit |
| * @return a Future representing pending completion of the task |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| * @throws NullPointerException if the task is null |
| */ |
| Future<V> submit(Callable<V> task); |
| |
| /** |
| * Submits a Runnable task for execution and returns a Future |
| * representing that task. Upon completion, this task may be |
| * taken or polled. |
| * |
| * @param task the task to submit |
| * @param result the result to return upon successful completion |
| * @return a Future representing pending completion of the task, |
| * and whose <tt>get()</tt> method will return the given |
| * result value upon completion |
| * @throws RejectedExecutionException if the task cannot be |
| * scheduled for execution |
| * @throws NullPointerException if the task is null |
| */ |
| Future<V> submit(Runnable task, V result); |
| |
| /** |
| * Retrieves and removes the Future representing the next |
| * completed task, waiting if none are yet present. |
| * |
| * @return the Future representing the next completed task |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| Future<V> take() throws InterruptedException; |
| |
| |
| /** |
| * Retrieves and removes the Future representing the next |
| * completed task or <tt>null</tt> if none are present. |
| * |
| * @return the Future representing the next completed task, or |
| * <tt>null</tt> if none are present |
| */ |
| Future<V> poll(); |
| |
| /** |
| * Retrieves and removes the Future representing the next |
| * completed task, waiting if necessary up to the specified wait |
| * time if none are yet present. |
| * |
| * @param timeout how long to wait before giving up, in units of |
| * <tt>unit</tt> |
| * @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| * <tt>timeout</tt> parameter |
| * @return the Future representing the next completed task or |
| * <tt>null</tt> if the specified waiting time elapses |
| * before one is present |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException; |
| } |