Re: [Dev-C++] C keyword 'volatile'

[<a_g...@ya...>]

I think that is the most important use. Really good answer. It is also used when working with shared memory between UNIX or UNIX like OSs.
Another interesting use of this variable is in the OS VxWorks, which has a flat gobal memory architechture. All globals are by default shared between all 'tasks', and so volatile is used there quite efficiently



Zodiaq <zo...@ac...> wrote:
Hello Louis and all Dev-C++ users,

Thursday, June 19, 2003, 3:14:13 PM, Louis wrote as follows:

LG> Can anyone explain the C keyword 'volatile'
LG> as in the statement: volatile int x;

LG> What does this do to variable x ? when does one need to use it ?

volatile is very interesting keyword - it does nothing to variable but
does something IMPORTANT to compiler optimization concering this
variable... and what it does? It turns OFF optimizations like checking
value of variable... normally variable value might be checked once in
a loop (if it does not change during the loop) at first use but with
volatile you force compiler to ALWAYS check it even if use it inside a loop...
where is this keyword mainly used?? Hmmm... from my point of view its
use is mainly useful in multithreaded application to check statesments
that other threads might set - in few of my apps main thread launches
child threads to do some work... this work is sometime very time
consuming, so if user decides to stop this thread main thread sets one
variable of child thread (lets say named Stopped) to true so its knows
to stop working... before it returns it makes memory cleanup - frees
memory used by thread... If I would just kill it (using
TerminateThread) I'd get memory leaks - memory that child thread
allocated isn't freed if it's stopped by TerminateThread... so child
just checks this Stopped variable in few places (in loops of course)
and if its value changes to true it knows to free memory and return...
without volatile on Stopped thanks to compiler optimisations this
child thread might never know that this value changed - child thread
did not change it so why to check its value so often??? volatile does
the job! I don't know about any other usages of volatile, but I'd
gladly hear about some...

-- 
regards, Zodiaq



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