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The Volatile Modifier

Started by Evil Bill Jul 22, 2002 at 4:25 PM 4 replies 250+ views

Original Post

Jul 22, 2002 at 4:25 PM

I''m writing a small chat program with WinSock, and i was wondering if people ever use the volatile modifier. My code goes like this:

  
DWORD Socket::ListenThreadProc()
{
   s_bListenThreadActive = TRUE;
   while(s_bListenThreadActive)
   {
   }
   return 0;
}

where "s_bListenThreadActive" is a volatile static BOOL. When the socket is closed, s_bListenThreadActive is set to FALSE, so the thread proc exits. As i said, do people ever use the volatile keyword? Cheers, Steve Steve
DirectX Programmer
Soon to be the new Bill Gates

niyaw

Jul 22, 2002 at 4:31 PM

i always do.

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Anon Mike

117

Anon Mike

Jul 22, 2002 at 7:34 PM

If you don''t your app will probably fail when you build in release mode because the while loop will be optimized away and you''ll go into an infinite loop.

Evil Bill

Author

Evil Bill

Jul 22, 2002 at 7:40 PM

Yeah, thats what i was thinking.
I only ask because i only discovered this a wee while ago, and it hasn''t been mentioned in any multi-threading tutorials i''ve seen - probably because this is a really bad way to do it

I''ve changed my code anyway, so i don''t use threads.

Thanks for the replies, Steve

Steve
DirectX Programmer
Soon to be the new Bill Gates

Shannon Barber

Mod

368

Shannon Barber

Jul 22, 2002 at 9:45 PM

That''s not a bad way to do it, it''s simple & it works - so long as that bool is volatile

BaelWrath

Jul 23, 2002 at 1:51 AM

Volatile bools arent so bad but if you are ever using something more complicated (say to hold an interupt value) I suggest you copy the value to another variable first then test on the none volatile variable.

This is because the system reads a volatile variable every time it finds it, even if you are using it twice on the same line (say in a case to select a number of subprocedures with the value as a paramter). In other words it can change after the test.

They also make a mess of any optimisation and because of the ''always read'' premise can increase the number of cycles a loop uses quite dramatically.

Regards

BaelWrath

If it is not nailed down it''s mine and if I can prise it loose,
it''s not nailed down!

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