非常感谢您的所有建议！
最后，我选择了一些我认为相当简单的东西。我发现CountDownLatch几乎是我所需要的。它会一直阻塞，直到计数器达到 0。唯一的问题是它只能倒计时，不能倒计时，因此在我的动态设置中不起作用，任务可以提交新任务。CountLatch因此，我实现了一个提供附加功能的新类。（见下文）然后我使用这个类如下。
主线程调用latch.awaitZero()，阻塞直到latch达到0。
任何线程，在调用executor.execute(..)调用之前latch.increment()。
任何任务，就在完成之前，调用latch.decrement().
当最后一个任务终止时，计数器将达到 0，从而释放主线程。
欢迎进一步的建议和反馈！
public class CountLatch {
@SuppressWarnings("serial")
private static final class Sync extends AbstractQueuedSynchronizer {
Sync(int count) {
setState(count);
}
int getCount() {
return getState();
}
protected int tryAcquireShared(int acquires) {
return (getState() == 0) ? 1 : -1;
}
protected int acquireNonBlocking(int acquires) {
// increment count
for (;;) {
int c = getState();
int nextc = c + 1;
if (compareAndSetState(c, nextc))
return 1;
}
}
protected boolean tryReleaseShared(int releases) {
// Decrement count; signal when transition to zero
for (;;) {
int c = getState();
if (c == 0)
return false;
int nextc = c - 1;
if (compareAndSetState(c, nextc))
return nextc == 0;
}
}
}
private final Sync sync;
public CountLatch(int count) {
this.sync = new Sync(count);
}
public void awaitZero() throws InterruptedException {
sync.acquireSharedInterruptibly(1);
}
public boolean awaitZero(long timeout, TimeUnit unit) throws InterruptedException {
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
}
public void increment() {
sync.acquireNonBlocking(1);
}
public void decrement() {
sync.releaseShared(1);
}
public String toString() {
return super.toString() + "[Count = " + sync.getCount() + "]";
}
}
请注意，可以将increment()/decrement()调用封装到自定义的Executor子类中，例如 Sami Korhonen 所建议的，或者impl 所建议的with beforeExecuteand 。afterExecute看这里：
public class CountingThreadPoolExecutor extends ThreadPoolExecutor {
protected final CountLatch numRunningTasks = new CountLatch(0);
public CountingThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
@Override
public void execute(Runnable command) {
numRunningTasks.increment();
super.execute(command);
}
@Override
protected void afterExecute(Runnable r, Throwable t) {
numRunningTasks.decrement();
super.afterExecute(r, t);
}
/**
* Awaits the completion of all spawned tasks.
*/
public void awaitCompletion() throws InterruptedException {
numRunningTasks.awaitZero();
}
/**
* Awaits the completion of all spawned tasks.
*/
public void awaitCompletion(long timeout, TimeUnit unit) throws InterruptedException {
numRunningTasks.awaitZero(timeout, unit);
}
}