id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
7892,boost.atomic misbehaves with Apple clang version 4.1 and -O2,Andreas Beisler <ebfx@…>,timblechmann,"There seems to be an issue, when assigning to an atomic in a ""while (true)"" loop (without break statement!).

{{{
#include <boost/atomic.hpp>

void this_works()
{
    boost::atomic_bool b(false);
    std::cout << b << std::endl; // 0
    b = true;
    std::cout << b << std::endl; // 1
}

void this_works_too()
{
    boost::atomic_bool b(false);
    while (true)
    {
        std::cout << b << std::endl; // 0
        b = true;
        std::cout << b << std::endl; // 1
        break;
    }
}

void this_doesnt_work()
{
    boost::atomic_bool b(false);
    while (true)
    {
        std::cout << b << std::endl; // 0
        b = true;
        std::cout << b << std::endl; // 0
    }
}

// Issue arises when compiled with Apple LLVM 4.1 and -O2:
//     clang++ -O2 main.cpp

int main(int argc, char ** argv)
{
    this_works();
    this_works_too();
    this_doesnt_work();
    return 0;
}
}}}

This happens only when the optimization level is set to at least 2. It happens in clang++ 4.1, but works in clang++ 3.2. Maybe it's possible to work around that issue, since std::atomic works fine.

Best regards,
Andreas
",Bugs,closed,To Be Determined,atomic,Boost Release Branch,Problem,wontfix,,