标签：prot 融合 consumer 调用 完成 sync 委托 row produce
CompletionService和ExecutorCompletionService的实现
使用executor提交任务，接收类型future.get()获取结果的顺序是线程执行先后的顺序。
使用ExecutorCompletionService提交任务，CompletionService的take()方法接收future类型的返回值，获取的结果顺序是线程执行完毕的顺序
JDK源码中CompletionService的javadoc说明如下：
/** * 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. */
public ExecutorCompletionService(Executor executor) {
if (executor == null)
throw new NullPointerException();
this.executor = executor;
this.aes = (executor instanceof AbstractExecutorService) ?
(AbstractExecutorService) executor : null;
this.completionQueue = new LinkedBlockingQueue<Future<V>>();
}
public Future<V> submit(Callable<V> task) {
if (task == null) throw new NullPointerException();
RunnableFuture<V> f = newTaskFor(task);
executor.execute(new QueueingFuture(f));
return f;
}
QueueingFuture是FutureTask的一个子类，通过改写FutureTask类的done方法，可以实现当任务完成时，将结果放入到BlockingQueue中。
private class QueueingFuture extends FutureTask<Void> {
QueueingFuture(RunnableFuture<V> task) {
super(task, null);
this.task = task;
}
protected void done() { completionQueue.add(task); }
private final Future<V> task;
}
FutureTask.done()，这个方法默认什么都不做，就是一个回调，当提交的线程池中的任务完成时，会被自动调用。这也就说时候，当任务完成的时候，会自动执行QueueingFuture.done()方法，将返回结果加入到阻塞队列中，加入的顺序就是任务完成的先后顺序。
标签：prot 融合 consumer 调用 完成 sync 委托 row produce
原文地址：https://www.cnblogs.com/itfeng813/p/14659345.html
