Silly question about IORefs and MVars

Nicolas Oury
Sun, 17 Nov 2002 19:33:18 +0100

I have a silly question about IORefs and MVars.

When do we have to use MVars if a var is accessed by multiple threads. 
In fact, I wonder why IORefs updates aren't safe :
it seems that preemptive scheduling takes place during memory allocation 
and I can't see where there could be an allocation (and so a switch) in 
a read or a write of an IORef.

Related question : how less performant is a MVar comparated to simple 

best regards,
Nicolas Oury