How to stop a Java thread?

Question

Possible Duplicate:
How do you kill a thread in Java?
How to start/stop/restart a thread in Java?

Thread has the following functions:

destroy()
stop()
suspend()

but they are all deprecated.
What do you use to stop a thread?

You don't stop a thread, just make the `run` method finish its execution. — Luiggi Mendoza, Oct 21 '12 at 07:22
Could you elaborate on your use case on why you want to stop a thread? — Vikdor, Oct 21 '12 at 07:24
For completeness, the other way is to terminate the entire process - that will work. — Martin James, Oct 21 '12 at 08:28
set a flag outside the Thread or on a field in the Thread, and have the thread check when the flag changes to true. When it does, make the run method return. Set the flag to make the thread quit itself. simples — , Jun 25 '13 at 13:53

score 4 · Answer 1 · edited Jan 26 '13 at 10:34

4

You should make sure that it just runs through / exits itself when its supposed to.

Check this for explanation.

edited Jan 26 '13 at 10:34

Make My World

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3

answered Oct 21 '12 at 07:24

Udo Held

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score 3 · Answer 2 · edited Dec 20 '14 at 12:29

You can use a boolean flag to stop the thread. Also you can make use of Thread.isInterrupted() to check if thread was interrupted and ignore the rest of the work same as boolean flag.

class Worker implements Runnable {
    private volatile boolean shouldRun = true;

    @Override
    public void run() {
        while (shouldRun) {
            // your code here
        }
    }

    public void cancel()
    {
        shouldRun = false;
    }
}

If you wan to know why these functions are deprecated you can check Java Thread Primitive Deprecation

score 2 · Answer 3 · answered Oct 21 '12 at 07:26

2

You could do it like this:

private boolean running = true;

public void stop () {
    running = false;
}    

public void run () {
    while (running) { 
        //your code goes here
    }
}

This is just a simple way of letting the run-method simply die out.

answered Oct 21 '12 at 07:26

Heskja

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1

+1 running needs to be `volatile` otherwise the run() might never stop. – Peter Lawrey Oct 21 '12 at 09:01

score 2 · Answer 4 · answered Oct 21 '12 at 07:27

You ask him politely to end it's work. The thread should be well behaved and it should end it's work when asked.

To ask you use Thread.interrupt() which will either throw in InterruptedException (if the thread is waiting) or set a flag in the thread (if not waiting).

The thread should then exit it's work when it catches an InterruptException or if it does a lot a long work (without sleep/wait) it should check from time to time if it was interrupted and exit if so.

score 0 · Answer 5 · answered Oct 21 '12 at 07:31

The methods you mentioned are deprecated because once used they could bring system to unstable state: it is just like kill process. Using these methods does not give the thread any chance to exit gracefully.

The conclusion is that each thread you are implementing should have its own mechanism for graceful exit. Typically you do the following. Create boolean flag exit that is false by default. The thread's run() method should implement loop like:

while (!exit) {
    // do the job
}

Add method exit() that turns this flag to true, so when the method is called from outside your thread will leave the while loop at the next iteration. You should care about closing resources etc when exiting.

Obviously you can improve the mechanism by sending sing

score 0 · Answer 6 · answered Oct 21 '12 at 07:44

Any thread runs to do its work. It should determine itself if there is more work to do. When you want to stop a working thread, this means the thread thinks the work exists, but you do not want the thread to do it. This is definitely a problem in your design. In a good designed problem, there is no need to stop/resume threads.

How to stop a Java thread?

6 Answers6