[Bug c++/55471] New: c++ mutex does not work as expected

["gustavo at atc dot ugr.es" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55471

             Bug #: 55471
           Summary: c++ mutex does not work as expected
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gustavo@atc.ugr.es


Created attachment 28780
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28780
source code with the bug

In a small test with a mutex it does not block all threads.

The bug is triggered by the place the mutex is declared:
* When the mutex is declared global it does not work.
* When it is a local variable it does work.#include <iostream>


#include <mutex>
#include <thread>

std::mutex m; // this program fails when m is a global variable

int main()
{
    const unsigned N = 10;
    // std::mutex m; // with m here everything is allright

    for(unsigned i = 0; i < N; ++i)
        new std::thread([&]()
        {
            while(true)
            {
                m.lock();
                std::cout << "[" << std::this_thread::get_id() << "]: ";
                for(unsigned i = 0; i < 10; ++i)
                    std::cout << i;
                std::cout << std::endl;
                m.unlock();
            }
        });

    std::this_thread::sleep_for(std::chrono::seconds(1));
}