Re: thread wait

Thomas Hawtin <>
Mon, 13 Aug 2007 00:20:50 +0100
korcs wrote:

I have a problem with suspending a thread.

It's really difficult to see what is happening with an incomplete
example. As Patricia mentioned, try to come up with a small but complete
program to demonstrate the problem.

Anyway, my thoughts on what you have selected:

As suspend() has deprecated I am trying to use the wait() - notify()
combination, but after the thread pauses it won't resume again.

Yes, look at the explanation. suspend can pause a thread whilst it is
holding a lock that you may not even be aware (perhaps in some library,
perhaps loading classes).

     class startListener implements ActionListener {

Class names should have initial caps.

Tabs work badly. Particularly in Usenet. My reader is displaying you
post indented inconsistently. Quoting doesn't help either.

             if(!clock.isAlive()) {


So clock is a thread. You can only start threads once. isAlive isn't a
good check. There is also a potential race from between isAlive, start
and the thread actually starting.

             threadsSuspended = true;

Technically this should be in a synchronised block matching reading of
the variable (you can use volatile, but that is very difficult to get

     public void run()

I'd suggest using an inner class, even if it just calls a private method
on the outer class.

Note that 'this' within an inner class refers to inner instance, not the
outer. Even Brian Goetz managed to publish a book with this mistake.

                 this.putText(new Integer(counter).toString());

I don't know the implementation of putText, but note that Swing
components should always be accessed on the AWT Event Dispatch Thread (EDT).

Integer.toString(counter) would be a better way of expressing that (or
String.valueOf(counter) if you must).

                synchronized(this) {
                    while (threadsSuspended)

Are you sleeping or waiting? (Unless it's a bug demonstration, I always
prefer timed wait to sleep as you can quite a wait without having to use
interrupt (which has some problems associated with it)).

         } // while

        } catch (InterruptedException e) {


Yay! Thread interrupts that actually interrupts rather than being
dropped and carrying on as normal.



Tom Hawtin

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