| 1 |
dl |
1.1 |
/* |
| 2 |
|
|
* Written by Doug Lea with assistance from members of JCP JSR-166 |
| 3 |
|
|
* Expert Group and released to the public domain, as explained at |
| 4 |
|
|
* http://creativecommons.org/publicdomain/zero/1.0/ |
| 5 |
|
|
*/ |
| 6 |
|
|
|
| 7 |
|
|
package java.util.concurrent; |
| 8 |
|
|
|
| 9 |
|
|
/** |
| 10 |
|
|
* A service that decouples the production of new asynchronous tasks |
| 11 |
|
|
* from the consumption of the results of completed tasks. Producers |
| 12 |
|
|
* <tt>submit</tt> tasks for execution. Consumers <tt>take</tt> |
| 13 |
|
|
* completed tasks and process their results in the order they |
| 14 |
|
|
* complete. A <tt>CompletionService</tt> can for example be used to |
| 15 |
|
|
* manage asynchronous I/O, in which tasks that perform reads are |
| 16 |
|
|
* submitted in one part of a program or system, and then acted upon |
| 17 |
|
|
* in a different part of the program when the reads complete, |
| 18 |
|
|
* possibly in a different order than they were requested. |
| 19 |
|
|
* |
| 20 |
|
|
* <p>Typically, a <tt>CompletionService</tt> relies on a separate |
| 21 |
|
|
* {@link Executor} to actually execute the tasks, in which case the |
| 22 |
|
|
* <tt>CompletionService</tt> only manages an internal completion |
| 23 |
|
|
* queue. The {@link ExecutorCompletionService} class provides an |
| 24 |
|
|
* implementation of this approach. |
| 25 |
|
|
* |
| 26 |
|
|
* <p>Memory consistency effects: Actions in a thread prior to |
| 27 |
|
|
* submitting a task to a {@code CompletionService} |
| 28 |
|
|
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
| 29 |
|
|
* actions taken by that task, which in turn <i>happen-before</i> |
| 30 |
|
|
* actions following a successful return from the corresponding {@code take()}. |
| 31 |
|
|
*/ |
| 32 |
|
|
public interface CompletionService<V> { |
| 33 |
|
|
/** |
| 34 |
|
|
* Submits a value-returning task for execution and returns a Future |
| 35 |
|
|
* representing the pending results of the task. Upon completion, |
| 36 |
|
|
* this task may be taken or polled. |
| 37 |
|
|
* |
| 38 |
|
|
* @param task the task to submit |
| 39 |
|
|
* @return a Future representing pending completion of the task |
| 40 |
|
|
* @throws RejectedExecutionException if the task cannot be |
| 41 |
|
|
* scheduled for execution |
| 42 |
|
|
* @throws NullPointerException if the task is null |
| 43 |
|
|
*/ |
| 44 |
|
|
Future<V> submit(Callable<V> task); |
| 45 |
|
|
|
| 46 |
|
|
/** |
| 47 |
|
|
* Submits a Runnable task for execution and returns a Future |
| 48 |
|
|
* representing that task. Upon completion, this task may be |
| 49 |
|
|
* taken or polled. |
| 50 |
|
|
* |
| 51 |
|
|
* @param task the task to submit |
| 52 |
|
|
* @param result the result to return upon successful completion |
| 53 |
|
|
* @return a Future representing pending completion of the task, |
| 54 |
|
|
* and whose <tt>get()</tt> method will return the given |
| 55 |
|
|
* result value upon completion |
| 56 |
|
|
* @throws RejectedExecutionException if the task cannot be |
| 57 |
|
|
* scheduled for execution |
| 58 |
|
|
* @throws NullPointerException if the task is null |
| 59 |
|
|
*/ |
| 60 |
|
|
Future<V> submit(Runnable task, V result); |
| 61 |
|
|
|
| 62 |
|
|
/** |
| 63 |
|
|
* Retrieves and removes the Future representing the next |
| 64 |
|
|
* completed task, waiting if none are yet present. |
| 65 |
|
|
* |
| 66 |
|
|
* @return the Future representing the next completed task |
| 67 |
|
|
* @throws InterruptedException if interrupted while waiting |
| 68 |
|
|
*/ |
| 69 |
|
|
Future<V> take() throws InterruptedException; |
| 70 |
|
|
|
| 71 |
|
|
/** |
| 72 |
|
|
* Retrieves and removes the Future representing the next |
| 73 |
|
|
* completed task or <tt>null</tt> if none are present. |
| 74 |
|
|
* |
| 75 |
|
|
* @return the Future representing the next completed task, or |
| 76 |
|
|
* <tt>null</tt> if none are present |
| 77 |
|
|
*/ |
| 78 |
|
|
Future<V> poll(); |
| 79 |
|
|
|
| 80 |
|
|
/** |
| 81 |
|
|
* Retrieves and removes the Future representing the next |
| 82 |
|
|
* completed task, waiting if necessary up to the specified wait |
| 83 |
|
|
* time if none are yet present. |
| 84 |
|
|
* |
| 85 |
|
|
* @param timeout how long to wait before giving up, in units of |
| 86 |
|
|
* <tt>unit</tt> |
| 87 |
|
|
* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| 88 |
|
|
* <tt>timeout</tt> parameter |
| 89 |
|
|
* @return the Future representing the next completed task or |
| 90 |
|
|
* <tt>null</tt> if the specified waiting time elapses |
| 91 |
|
|
* before one is present |
| 92 |
|
|
* @throws InterruptedException if interrupted while waiting |
| 93 |
|
|
*/ |
| 94 |
|
|
Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException; |
| 95 |
|
|
} |
