CompletonService任务提交和处理异步简单demo
public class TestCompletonService {
private final static ExecutorService executor = Executors.newFixedThreadPool(100);
public static void main(String[] args) throws InterruptedException, ExecutionException {
case1();
}
private static void case1() throws InterruptedException, ExecutionException {
List<String> list = new ArrayList<String>();
list.add("执行4");
list.add("执行3");
list.add("执行2");
list.add("执行1");
CompletionService<String> completionService = new ExecutorCompletionService<String>(executor);
for (final String t : list) {
completionService.submit(new Callable<String>() {
@Override
public String call() throws Exception {
int random = (new Random().nextInt(9)+1)*1000;
Thread.sleep(random);
return "执行完成:"+t+"耗时:"+random;
}
});
}
for (int i = 0; i < list.size(); i++) {
Future<String> take = completionService.take();
System.out.println(take.get());
}
}
}
CompletionService接口提供五个方法:
-
Future<V> submit(Callable<V> task)
提交Callable类型的task;由于ExecutorService extends Executor,所以执行时异步的 -
Future<V> submit(Runnable task, V result)
提交Runnable类型的task; -
Future<V> take() throws InterruptedException
获取并移除已完成状态的task,如果目前不存在这样的task,则等待;完成的任务放在阻塞队列里面,所以是阻塞的 -
Future<V> poll()
获取并移除已完成状态的task,如果目前不存在这样的task,返回null; -
Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException
获取并移除已完成状态的task,如果在指定等待时间内不存在这样的task,返回null。
有意思的是:
ExecutorService executor = Executors.newFixedThreadPool(100);;换成 Executors.newFixedThreadPool(1);执行结果是:
四个任务倒序提交给 CompletionService执行,CompletionService还是交给ExecutorService executor线程池里面的线程执行,但是只有一个线程,其他的任务放在LinkedBlockingQueue中等待执行,LinkedBlockingQueue最大大小是Integer.MAX_VALUE,LinkedBlockingQueue是FIFO,所以一次执行