currentThread().wait in applet gives IlleagalMonitorException

[Holger Wiechert]

Hi,

I tried to let an applet wait it's execution at some point for a few
seconds. The code looks like this:

public class Applet1 extends Applet
{
public void init()
{
//...
stopApplet();

}

private synchronized void stopApplet()
{

Thread currentThread=Thread.currentThread();
debug("waiting for 3 seconds...");
try
{
currentThread.wait(3000);
}
catch (java.lang.InterruptedException e) {}
debug("... it's over.");
}
}

Can anybody please tell me, why I get the following error and what to do in
order to let the applet wait?

Thanks for your time, Holger

waiting for 3 seconds...
java.lang.IllegalMonitorStateException: current thread not owner
at java.lang.Object.wait(Native Method)
at Applet1.stopApplet(Applet1.java:48)
at Applet1.init(Applet1.java:37)
at sun.applet.AppletPanel.run(AppletPanel.java:333)
at java.lang.Thread.run(Thread.java:479)

[Patricia Shanahan]

In order to use wait or notify, you need to be synchronized on the
object whose wait/notify you are going to use. In this case you are
synchronized on your Applet object, but waiting on the semaphore
associated with the newly created currentThread.

The purpose of wait is to wait for someone else to notify the waiting
thread of an event, and since you are waiting on a newly created thread
without telling anyone about it, you are unlikely to get notified.

If you just want the thread you are running in to sleep for 3 seconds,
use Thread.sleep(3000).

Patricia

[Konstantin A Goudkov]

Try currentThread.sleep(3000);

unless you need to notify that thread or it locks some synchronized clasess
you can use sleep(time)

"Holger Wiechert" <holger....@coconet.de> wrote in message
news:398aa3f7$1...@news.isis.de...

[Thomas Hawtin]

Konstantin A Goudkov wrote:

> Try currentThread.sleep(3000);

That's an incredibly misleading way to put it. Better is:

Thread.sleep(3000);

as sleep(long) and sleep(long,int) are static methods.

> "Holger Wiechert" <holger....@coconet.de> wrote in message
> news:398aa3f7$1...@news.isis.de...

> > private synchronized void stopApplet()
> > [...]
> > currentThread.wait(3000);
> > [...]

> > java.lang.IllegalMonitorStateException: current thread not owner

wait() is a method in Object. You need to synchronise to the same object
in order to wait or notify. So other than using sleep there are a number
of solutions available:

synchronized (currentThread) (
currentThread.wait(3000);
}

You probably don't want to synchronize onto your current thread.

wait(3000); // On this.

or

Object lock = new Object();
synchronized (lock) (
lock.wait(3000);
}

Probably best to use sleep(). Or better don't use multithreading at all.
Do a timed repaint() and check to see that the time has elapsed.
Threading is difficult, dangerous and can be resource intensive.

BTW: Never block in the AWT event dispatch thread, including file,
socket and URLConnection access but excluding guaranteed quick
synchronized blocks.

Tackline