有几种方法。
您可以先调用ExecutorService.shutdown，然后再调用ExecutorService.awaitTermination，它会返回：
如果此执行程序终止，则为 true，如果超时，则为 false
终止前
所以：
有一个函数叫做 awaitTermination 但是必须有一个超时
其中提供。这并不能保证当它返回所有
任务就完成了。有没有办法做到这一点？
您只需循环调用awaitTermination。
使用 awaitTermination
此实现的完整示例：
public class WaitForAllToEnd {
public static void main(String[] args) throws InterruptedException {
final int total_threads = 4;
ExecutorService executor = Executors.newFixedThreadPool(total_threads);
for(int i = 0; i < total_threads; i++){
executor.execute(parallelWork(100 + i * 100));
}
int count = 0;
// This is the relevant part
// Chose the delay most appropriate for your use case
executor.shutdown();
while (!executor.awaitTermination(100, TimeUnit.MILLISECONDS)) {
System.out.println("Waiting "+ count);
count++;
}
}
private static Runnable parallelWork(long sleepMillis) {
return () -> {
try {
Thread.sleep(sleepMillis);
} catch (InterruptedException e) {
// Do Something
}
System.out.println("I am Thread : " + Thread.currentThread().getId());
};
}
}
使用 CountDownLatch
另一种选择是创建一个CountDownLatch，其中count 等于并行任务的数量。每个线程调用countDownLatch.countDown();，而main线程调用countDownLatch.await();。
此实现的完整示例：
public class WaitForAllToEnd {
public static void main(String[] args) throws InterruptedException {
final int total_threads = 4;
CountDownLatch countDownLatch = new CountDownLatch(total_threads);
ExecutorService executor = Executors.newFixedThreadPool(total_threads);
for(int i = 0; i < total_threads; i++){
executor.execute(parallelWork(100 + i * 100, countDownLatch));
}
countDownLatch.await();
System.out.println("Exit");
executor.shutdown();
}
private static Runnable parallelWork(long sleepMillis, CountDownLatch countDownLatch) {
return () -> {
try {
Thread.sleep(sleepMillis);
} catch (InterruptedException e) {
// Do Something
}
System.out.println("I am Thread : " + Thread.currentThread().getId());
countDownLatch.countDown();
};
}
}
使用循环障碍
另一种方法是使用Cyclic Barrier
public class WaitForAllToEnd {
public static void main(String[] args) throws InterruptedException, BrokenBarrierException {
final int total_threads = 4;
CyclicBarrier barrier = new CyclicBarrier(total_threads+ 1);
ExecutorService executor = Executors.newFixedThreadPool(total_threads);
for(int i = 0; i < total_threads; i++){
executor.execute(parallelWork(100 + i * 100, barrier));
}
barrier.await();
System.out.println("Exit");
executor.shutdown();
}
private static Runnable parallelWork(long sleepMillis, CyclicBarrier barrier) {
return () -> {
try {
Thread.sleep(sleepMillis);
} catch (InterruptedException e) {
// Do Something
}
System.out.println("I am Thread : " + Thread.currentThread().getId());
try {
barrier.await();
} catch (InterruptedException | BrokenBarrierException e) {
// Do something
}
};
}
}
还有其他方法，但这些方法需要更改您的初始要求，即：
提交后如何等待所有任务完成
使用 ExecutorService.execute() 。