Re: Are lock free algorithms possible in C++?
On 2010-07-12 03:22:44 -0400, Andy said:
Assuming I've got an atomic & fenced CAS instruction available via a
library; is it possible to use this to write a lock free algorithm in C
++?
Although the memory fence would prevent hardware re-ordering I'm
worried that compiler could reorder memory access rendering the fence
useless. For example consider the below, grossly simplified example:
bool continue = true;
while(continue) {
while(isLocked) { }
// atomically set isLocked to true if it has the value false
if(AtomicTestAndSet(&isLocked, true, false)) {
continute = false;
}
}
SharedStdVector[3] += 10;
Is there anything that prevents the compiler from reordering the
access to SharedStdVector so that it is executed before mutex is
aquired? Is there anything I can do to prevent such reordering?
It depends on the compiler. But C++0x will have atomic variables and
the implementation will take care of the compiler-specific techniques
to prevent reordering.
--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The Standard C++ Library Extensions: a Tutorial and Reference (www.petebecker.com/tr1book)
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