event queue:
check queue:
	time	eid	pid	event
	10	1	1	X.x := true
event queue:
check queue:
	time	eid	pid	event
	12	3	1	X.R!(X.x)
M! is in check queue, but will block 
event queue:
check queue:
	(empty)
time: 12
queue should be empty, we have deadlock 
