[fpc-devel] volatile variables
mschnell at lumino.de
Wed Jun 29 16:31:32 CEST 2011
On 06/29/2011 03:17 PM, Nikolai Zhubr wrote:
> All places where any non-readonly data could be accessed by 2 or more
> threads should be protected. Thats it.
So this is not supposed to work:
myThread := TmyThread.Create(True);
while not myThread.Suspended sleep(0); //give up time slice to
allow the worker thread to start
myList := TThreadlist.Create; // set the variable
in cache 1
myThread.Suspended := False;
sleep(100); // have the
worker thread run
myList := NIL; // set the variable in the
Suspended := True;
myList.Add(..... //has the variable been
synchronized from the other cache ????
Here the variable myList is not protected.
As assigning a value to myList in one thread is only a very short time
before the other thread reads it, it's very likely that the wrong value
is still be in the cache of the worker thread's processor and make it
But is is just a very extreme example of a behavior that mostly is
assumed to work and according to your wording would be bound to fail.
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