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IllegalMonitorStateException

Posted on 2000-04-30
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Last Modified: 2012-06-22
How to avoid IllegalMonitorStateException with wait?

here is my code:

public class OutServerPool extends Thread {
  OutServer server;
  private Vector v;
public OutServerPool(OutServer server) {
  super();
  this.server=server;
  v=new Vector();
}
public synchronized void close() {
  if (this.isAlive())
    this.stop();
    server=null;
    v=null;
}
public synchronized Message poll() {
  if (v.size()==0)
    return null;
  Message msg=(Message)v.elementAt(0);
  v.removeElementAt(0);
  return msg;
}
public synchronized void push(Message msg) {
  v.addElement(msg);
  this.resume();
}
public void run() {
  while (true) {
    Message msg=null;
    while ((msg=poll())!=null) {
      if (server.oos!=null) {
        try {
          server.oos.writeObject(msg);
        } catch (Exception e) {
          System.err.println(this.getClass().getName()+":"+e);
          server.quit();
        }
      }
    }
    try {
      this.wait(); // raise the IllegalMonitorException always
    } catch(InterruptedException e) {
  }
}
}

Is there something that I don't know about wait() ?

Please help me.
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Question by:threshold
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Accepted Solution

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adam923 earned 100 total points
ID: 2765253
yes there is, you must call wait from within a synchronized method (or block)
if you do otherObject.wait() then it must be synchronized for that other object.
the reason for this is that wait means "give up the lock and pause this thread until notified" so it only makes sense when you have the lock on that object
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by:threshold
ID: 2765263
This question has a deletion request Pending
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by:adam923
ID: 2765267
This question no longer is pending deletion
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Expert Comment

by:adam923
ID: 2765268
please explain why you wish to delete the question?
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Author Comment

by:threshold
ID: 2765461
Sorry, because I found the answer in the other Questions.

And, I try to replace wait/notify with  suspend/resume. It is successful.

Sorry, i hadn't notice your comment when I deleted the question.
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Expert Comment

by:adam923
ID: 2766543
i'd suggest that you not use suspend and resume, they're very dangerous and have since been removed from the language completely.  wait and notify should be all you need for thread management.... suspend and resume will shoot you in the foot quickly!
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Author Comment

by:threshold
ID: 2768712
You r right!

For your suggestion, I fixed the code with wait/notify.

Thank you for your help.
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by:adam923
ID: 2770580
you're welcome
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