java.lang.IllegalMonitorStateException: object not locked by thread before wait()

Question

But I am synchronizing on the 'roster' object everywhere it gets new'ed. How come ?

The offending code:

 public Roster getRoster() {
    if (roster == null) {
        return null;
    }

    if (!roster.rosterInitialized) {
        try {
            synchronized (roster) {
                roster.reload();
                long waitTime = SmackConfiguration.getPacketReplyTimeout();
                long start = System.currentTimeMillis();
                while (!roster.rosterInitialized) {
                    if (waitTime <= 0) {
                        break;
                    }
                    roster.wait(waitTime);
                    long now = System.currentTimeMillis();
                    waitTime -= now - start;
                    start = now;
                }
            }
        }
        catch (InterruptedException ie) {
            // Ignore.
        }
    }
    return roster;
}

Answer 1

With "gets new'ed" you mean you create a new roster object?

Are you sure you are synchronizing correctly? Synchronizsation happens on instances, not on variables. So if you do e.g.

synchronized(roster) {
  roster = new Roster();
  // do something
}

Then you only synchronized to the old, not the new roster.

So the following code should produce the same error:

Roster roster = new Roster();
Roster othervariable = roster;
synchronized(othervariable) {
  roster = new Roster(); // create a new roster
  othervariable.wait(1000); // OK, since synchronized with this instance!
  roster.wait(1000); // NOT OK, not synchronized with *new* roster!
}

Synchronizsation does not happen on the name of the variable, but on the contents. If you overwrite the contents, you do not re-synchronize to the new value!