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Groups > comp.lang.java.programmer > #32938

Re: thread sleeping until event

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On 10/27/2015 5:41 AM, Philipp Kraus wrote:
> Hello,
>
> I have got a main thread running which can be stay in a pause definition. At the moment the main structure is:
>
> volatile boolean mypause = true;
>
> public voud run()
> {
> while (true)
> {
>      if (mypause)
>           Thread.sleep(1000);
>
>      // thread is working
>
> }
> }
>
> public void pause()
> {
>     mypause = !mypause;
> }
>
>
>
>
> If mypause is switch to false the thread should running. So my question is, how can I do a good pause state, so the thread create minimal system  load.

     There are several ways.  The "traditional" approach is to use
wait() and notify() or notifyAll():

	private boolean paused = true;

	public void run() {
	    while (true) {
	        synchronized(this) {
	            while(paused) {
	                this.wait();
	            }
	        }
	        do_work();
	    }
	}

	public synchronized void pauseOrResume() {
	    paused = !paused;
	    this.notifyAll();
	}

(I wrote the "this." pieces for clarity's sake; they could be omitted.)

     A few remarks:

     - Your pause() method, which I renamed to pauseOrResume() to better
       indicate what it does, seems peculiar.  An external agency might
       know when it wants the thread to start working, but it won't know
       when to tell the thread *not* to work: It doesn't know whether the
       thread has or has not yet seen the "Go" sign.

     - Along the same lines, I find it surprising that the worker thread
       does not set `paused' to true after (or before) do_work().  As it
       stands, the thread will just run and run and run until an external
       caller flips the `paused' switch.

     - The pause() method in your original code is *not* thread-safe.  It
       manipulates a `volatile' variable, yes, but it both reads *and*
       writes the value.  The read is thread-safe and so is the write,
       but the two operations taken as a pair are not.  That's why I used
       `synchronized' to guard the variable.

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM

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thread sleeping until event Philipp Kraus <philipp.kraus.flashpixx@gmail.com> - 2015-10-27 02:41 -0700
  Re: thread sleeping until event Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-27 08:36 -0400
    Re: thread sleeping until event Philipp Kraus <philipp.kraus.flashpixx@gmail.com> - 2015-10-27 14:22 -0700

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