Re: Threading : What's wrong with this ?

Mark Space <>
Sun, 20 Jul 2008 14:03:03 -0700
Patricia Shanahan wrote:

Ian Semmel wrote:

    public void run ()
        this.taskQ = new LinkedBlockingQueue<Object> ();

            taskQ.wait ();
        catch ( InterruptedException ie )
            System.out.println ( ie.getMessage () );
            System.exit ( 255 );

Exception is "java.lang.IllegalMonitorStateException: current thread
not owner" on the wait()

Seeing as how I just created the Q, what thread is the owner ?

PS I don't know much about java.

Given the PS, I'm going to question the assumption that you should be
calling taskQ.wait at all. For example, if you just want to suspend
until you can remove an item from taskQ, call taskQ.take().

This is a superb point. If the OP is merely trying to learn about the
basics of synchronization, he could use any object. Objects in
java.util.concerent are not required.

Runnable myRunnable = new Runnable() {
   String hello = "Hello WOrld!\n";
   public void run() {
    try {
     synchronize( hello ) {
    } catch( InterruptedException ex ) {

Does exactly the same thing as the op's (corrected) example. (Note: I
didn't compile or spell check that at all.)

offer() and take() look like they are much better alternatives when
using a BlockingQueue. I haven't read the API carefully, but I'm sure
that offer(), take() and most other methods are synchronized already,
which means you don't have to synchronize on the object yourself. It's
done for you. The OP may be missing this essential point.

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