Interface - java.util.concurrent.CompletionService
Created by : Mr Dk.
2021 / 02 / 16 🧧 19:03
Ningbo, Zhejiang, China
Definition
该接口将 提交新的异步任务 与 消费已完成任务产生的结果 解耦。生产者调用 submit() 提交任务，消费者调用 take() 按照任务完成的顺序获取完成的任务并处理结果。该接口的实现类可用于管理异步 I/O：
- 读取任务在程序的某个部分被提交到该服务中
- 程序的另一部分处理读取完成后的结果
本接口的实现类内部依赖于一个独立的执行器来真正执行任务，本接口定义的函数仅用于管理内部的 完成队列 - 队列中存放所有已完成的任务。
/**
* A service that decouples the production of new asynchronous tasks
* from the consumption of the results of completed tasks. Producers
* {@code submit} tasks for execution. Consumers {@code take}
* completed tasks and process their results in the order they
* complete. A {@code 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.
*
* <p>Typically, a {@code CompletionService} relies on a separate
* {@link Executor} to actually execute the tasks, in which case the
* {@code CompletionService} 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> {
}
Submit
将任务提交给执行器执行，并返回一个 Future 对象。当任务完成后，将可以从完成队列中取出。
/**
* 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 {@code get()} 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);
Take
从完成队列中取得并移除下一个已经完成的任务。如果队列中暂时没有任何已完成任务，则阻塞等待。
/**
* 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;
Poll
从完成队列中取得并移除下一个已经完成的任务。如果队列中暂时没有任何已完成任务，则返回 null。可选超时参数，使函数阻塞到超时时间再返回。
/**
* Retrieves and removes the Future representing the next
* completed task, or {@code null} if none are present.
*
* @return the Future representing the next completed task, or
* {@code null} 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
* {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
* {@code timeout} parameter
* @return the Future representing the next completed task or
* {@code null} 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;