Re: C++ Threads, what's the status quo?
Le Chaud Lapin wrote:
Mirek Fidler wrote:
Ahh... I guess you should seriously reconsider the issue.
Recommended reading is e.g. google: "why double checked guard does not
work".
Just for starters, if you have
Shared y;
Mutex y_lock;
void fn() {
y_lock.Lock();
y = 10;
y_lock.Unlock();
}
nothing in C++ standard prevents C++ compiler to generate machine code
equivalent to
void fn() {
y = 10;
y_lock.Lock();
y_lock.Unlock();
}
Are you saying that the C++ standard does not prescribe sequential
execution of statements in a single-threaded program?
Yes. It just prescribes that observable behavior is the same as if
statements were executed in sequential order. In this case, if compiler
is able to detect that Lock and Unlock do not touch y, it can produce
the code above.
If that is the case, then I could write a single-threaded application
that would not behave as a programmer would expect using an example
very similar to the one you gave.
No, see above.
Also, do you have a link regarding the quote above for Google? I
looked, and did not find what I think you were suggesting.
Well, I suggested that quote not because of particular pattern, but
because discussion of problems nicely introduces you to associated
troubles.
--
Mirek Fidler
U++ team leader. http://www.ultimatepp.org
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