Bug 317908

Description Phil Xue 2010-06-24 23:12:55 EDT

Build Identifier: 1.3.0.20100615-1704

Symptom: 
Wizard hangs with all UI components in disabled state. UIThread waits indefinitely on ModalContext$ModalContextThread.block() (thread dump attached)

Condition to Reproduce:
Run IRunnableWithProgress in a separate thread (ModalContextThread) in Wizard
IRunnableContext#Run(true, false, IRunnableWithProgress)

Cause:
The problem starts from when ModalContext is finishing run() method, in its finally block, it does these 3 things:
1. dispatches all queued events and wait for them to finish before running this run() which does nothing.
display.syncExec(new Runnable() {
	public void run() {
		// do nothing
	}
});

2. sets continueEventDispatching to false so the loop will exit in block()
continueEventDispatching = false;

3. wakes UIThread force event loop to exit
display.asyncExec(null);

The UIThread is blocked on ModalContext$ModalContextThread.block()#display.sleep() before (1) was called.
When (1) is executed ModalContextThread will be blocked until its empty run() method is called, in the meanwhile this wakes
up UIThread from display.sleep() which starts processing queued events with display.readAndDispatch() in UIThread, 
the last queued event is the empty run() in (1), when its turn comes the ModalContextThread will be waken up to execute
the empty run() method and eventually unblocks display.syncExec and continue to (2), at this point of time UIThread
and ModalContextThread are running concurrently. Deadlock happens when ModalContextThread finishes (2) and (3) before 
UIThread enters block()#display.sleep(), which causes UIThread to wait forever.


Workaround: 
1. set folk to false (run runnable in current thread)
2. move the wizard with mouse drag which initiates an UI update request that would wake the UIThread

Reproducible: Always