July 24, 2009
[J2ME] deadlock in canvas.paint, lcdui
If you need to have a critical section in Canvas.paint() override, double-check that you do not lock in same monitor when calling myCanvas.repaint(). Problem exists in this some specific configuration, when you have 2 threads. In [1, main for example] you do:
display.setCurrent(myCanvas); and in [2, newly created] you call:
myCanvas.repaint() in same critical section as in your paint() impl.
I had deadlock in this case, at least in some LCDUI implementations. The reason is that MIDP usually have its own critical section in setCurrent() (when calling paint() for the first time) and in repaint() (when adding repaint event into queue), so it cannot both add repaint request into queue and enter your paint()'s your critical section. Deadlock. So be careful ;-)
display.setCurrent(myCanvas); and in [2, newly created] you call:
myCanvas.repaint() in same critical section as in your paint() impl.
I had deadlock in this case, at least in some LCDUI implementations. The reason is that MIDP usually have its own critical section in setCurrent() (when calling paint() for the first time) and in repaint() (when adding repaint event into queue), so it cannot both add repaint request into queue and enter your paint()'s your critical section. Deadlock. So be careful ;-)
Labels: concurrency, critical section, deadlock, j2me, java, lcdui, multithreading, programming, synchronized, thread
