From: Ray Tomlinson <###@###.###>
To: ###@###.###
Cc: ###@###.###
Subject: JDialog.setVisible fails to notify waiting thread
Date: Fri, 14 Nov 1997 12:02:13 -0500

The setVisible method of JDialog contains a race: super.setVisible is done
after notifyAll with the result that a thread waiting in blockingShow may
be activated, find that the dialog is still visible, and continue waiting.
After this, the thread setting visibility false continues, the dialog
becomes invisible and the blockingShow thread stays blocked -- forever.

Below is the relevant bytecode:

Method void setVisible(boolean)
   0 iload_1
   1 ifne 27
   4 aload_0
   5 invokevirtual #75 <Method boolean isVisible()>
   8 ifeq 27
  11 aload_0
  12 astore_2
  13 aload_2
  14 monitorenter
  15 aload_0
  16 invokevirtual #76 <Method void notifyAll()>
  19 aload_2
  20 monitorexit
  21 goto 27
  24 aload_2
  25 monitorexit
  26 athrow
  27 aload_0
  28 iload_1
  29 invokespecial #86 <Method void setVisible(boolean)>
  32 return

The corresponding source (which Sun has failed to provide), but deduced
from the bytecode is:

public void setVisible(boolean newVisible)
{
  if (!newVisible && isVisible()) {
    synchronized(this) {
      notifyAll();
    }
  }
  super.setVisible(newVisible);
}

The code should probably be:

public void setVisible(boolean newVisible)
{
  boolean doNotify = (!newVisible && isVisible());
  super.setVisible(newVisible);
  if (doNotify) {
    synchronized(this) {
      notifyAll();
    }
  }
}

Ray Tomlinson


From: Scott Violet <sky@southampton>
To: ###@###.###
CC: swing-feedback@taller
Subject: Re: JDialog.setVisible fails to notify waiting thread
Date: Fri, 14 Nov 1997 11:09:09 -0800

Hi,
   Thanks for the excellent diagnosis of the bug! You are correct,
super.setVisible() is incorrectly being messaged after notifyAll() is
messaged. We will change this for a future release.
Thanks again,

-Scott Violet (###@###.###)