Fixed Thread Pool is exiting immediately, not processing threads

问题

Trying to understand fixed thread pools I made this test code, which revealed the below results, contrary to what I thought it would do:

Thread Start: 1
Thread Start: 2
Thread Start: 0

That's it. No "Thread End" messages and only 3 threads were started.

I expected and I want all 10 tasks to complete.

ExecutorService exec = Executors.newFixedThreadPool(3);

for (int c = 0; c < 10; c++) {
    exec.execute(new TestThread(c));
}
exec.shutdown();

---

public class TestThread implements Runnable {

    private int counter;

    public TestThread (int counter) {
        this.counter = counter;
    }

    @Override
    public void run() {
        System.out.println("Thread Start: " + counter);

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Thread End: " + counter);
    }
}

回答1:

exec.shutdown() doesn't block main thread. If you need to wait for all submitted tasks to finish you need to call exec.awaitTermination(1, TimeUnit.HOUR); (of course with timeout that makes sense for your application) after call to exec.shutdown();.

/**
 * Blocks until all tasks have completed execution after a shutdown
 * request, or the timeout occurs, or the current thread is
 * interrupted, whichever happens first.
 */
boolean awaitTermination(long timeout, TimeUnit unit)
    throws InterruptedException;

来源：https://stackoverflow.com/questions/52632916/fixed-thread-pool-is-exiting-immediately-not-processing-threads