Subj : Re: acquiring a new value/ without any mutexes
To   : comp.programming.threads
From : David Schwartz
Date : Wed Jan 05 2005 01:35 am


"John Torjo" <jtorjo@yahoo.com> wrote in message 
news:c638aac5.0406301104.4c79808d@posting.google.com...
> Hi to all you thread gurus,
>
> Small question:
> Say on a multi-processor machine I do something like this:
>
> // global variable
> int i = 0;
>
> // at some point in time,
> // when there are a lot of threads started
> // from one thread
> //
> // (NO mutexes/thread locks at all)
> i = 10;
>
>
> Am I guaranteed that at some point in time ALL threads will get the
> new value of i,as being 10 (as opposed to manually having to do a lock
> in order for a thread to get the latest value of i - as being 10)?

    No, you are not. Specifically, code like:

while(i==0) foo();

    Will likely *never* see the new value.

> I would assume so. So, I will go for the second question:
>
> What's the longest time it could take for a thread until it will
> acquire this value (10)? Would it be safe to assume that is the order
> of 1 millisecond, at most?

    It can be arbitrarily long.

    DS

.