Java-在使用者正在等待并且tomcat关闭时停止线程

Question

I have a servlet, and it is a singleton.

In the init, I create the producer and the consumers.

consumer = new MyThread();
consumer.start();

and the method run is like this:

@Override
public void run() {
    while (!isShutdown()) {
        if (queue.isEmpty())
            queue.wait();
        else
            ...
    }
}

then i have the destroy method. that set shutdown to true and I use .join

        consumer.setShutdown(true); 
        consumer.join();

but the method .join got lock.. and never finishes. If I change the queue.wait to Thread.sleep(), it works... but I don't want to change... what I'm doing wrong?

if I don't finish the thread, I got it: SEVERE: The web application [/test] appears to have started a thread named [Comsumer0] but has failed to stop it. This is very likely to create a memory leak.

Answer 1

Most likely the queue is empty and since you have shutdown you never send anything into the queue to cause it to wake up.

Fix this either by sending a dummy message to the queue after setting the shutdown flag or by just removing the shutdown flag completely and sending a shutdown command to the queue.

Also be aware that if your shutdown flag is not volatile (or AtomicBoolean ) then one thread may not see it being set by the other due to caching inside the CPU.

Answer 2

This is what the BlockingQueue is for:

    BlockingQueue queue = new ArrayBlockingQueue(5);
    // ...
    while (!isShutdown()) {
        Object poll = queue.poll(5, TimeUnit.SECONDS);
    }

Answer 3

you should change the design as advised above, or if you don't want to change your code, change your setShutdown() method body and statement to notify the queue.

public void setShutdown(boolean shutdown) {
  this.shutdown = shutdown;
  this.queue.notifyAll();
}

Answer 4

Using wait/notify methods is the old way to create a Consumer-Producer pattern.

It is better to use BlockingQueue.

BlockingQueue.put() - for Producer, and BlockingQueue.poll() - for Consumer.

BlockingQueue hides wait method underneath BlockingQueue.poll , BlockingQueue.put and will block a Consumer thread until Producer adds value to queue.

To fix the example above, you should make it wait for a finite amount of time like queue.wait(1000) , or wake consumer thread explicitly calling queue.notify() .