Description Gary Johnston 2007-09-21 17:19:39 EDT

Build ID: I20070625-1500

Steps To Reproduce:
I'm trying to make some test automation code perform a drag & drop.  I'm using Display.post(Event event) to send user input events.  Following is an outline of how I do DnD.  Note that this is running on a separate thread (i.e., not on the UI/display thread).  Display.post(Event) doesn't require being on the display thread.

1. Post a MouseMove event to move the cursor to the location of the drag
   source.
2. Post a MouseDown (button 1) event.
3. Post a series of MouseMove events that move the cursor 
   one pixel at a time in order to trigger drag detect.
4. Post a MouseMove event to move the cursor to the location
   of the drop target.
5. Post a MouseUp (button 1) event.

On Windows this works for me.  But on GTK it hangs in Display.post(Event) in the call to OS.GDK_DISPLAY() when it tries to post the first MouseMove event in step 3 (i.e., trying to post the first MouseMove after posting the MouseDown).

More information:
If I set a breakpoint and suspend the whole VM just before the problematic MouseMove attempt I find that the display thread is sleeping in a read/dispatch loop within its windowproc.  It looks like it is waiting for user input events to cause drag detect (or not).  I also find that if I try to step my own thread through its MouseMove call to Display.post(Event) it gets blocked in the call to OS.GDK_DISPLAY(). Resuming the display thread doesn't unblock it.

So it looks like an unavoidable deadlock situation.  I cannot see a way to post the necessary user input events without getting this deadlock.