Re: [Boost-users] Thread cancellation

From: Paul (elegant_dice_at_[hidden])
Date: 2005-02-10 19:46:32

> Synchronous cancellation may be simulated by setting a simple flag 
> polled by the cancellable thread.  (Appropriate memory barriers must be 
> placed after setting and before polling the flag.  In the absence of 
> portable memory barrier facilities, one may protect the flag with a 
> mutex, though that's annoyingly heavyweight.)  However this does not 

just out of curiousity, why do you think you need a memory barrier on a 
flag?  you would have 1 writer and 1 reader...  either the reader reads 
false or true, and once the writer has set it to true... thats it, the 
reader will read true on the next pass.

even if the reader is reading the same time as the writer is writing, 
and byte-sized memory writes are not atomic (which i think they are), 
then the read will still evaluate to true, which is what is desired anyway.

so theres no need for a mutex in this case?   even if there were 
multiple writers, its a one-way flag set operation, all would be trying 
to set the flag to true if all were writing at the same time, so all 
would get the desired result?

thanks
Paul