[Boost-bugs] [Boost C++ Libraries] #12394: boost::lockfree::queue with gcc-4.6 + optimization

Subject: [Boost-bugs] [Boost C++ Libraries] #12394: boost::lockfree::queue with gcc-4.6 + optimization
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-08-15 15:21:25

#12394: boost::lockfree::queue with gcc-4.6 + optimization
------------------------------+--------------------------
 Reporter:  ygabay@…          |      Owner:  timblechmann
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  lockfree
  Version:  Boost 1.58.0      |   Severity:  Problem
 Keywords:  lockfree, queue   |
------------------------------+--------------------------
 I am seeing a potential issue with lockfree queue when using gcc-4.6 with
 compilation optimization turned on.

 The behavior i'm seeing is that call to push() which returns true does not
 guarantee that the pushed element is consumable immediately. (i.e. a
 subsequent call to pop() might return false. after further debugging it
 seems like the element _will become_ consumable but it might take few more
 cpu cycles till this happens. this issue is not happening when turning the
 compiler optimizations off or when using gcc-4.8.

 here is the test program i am using to reproduce the issue, which is
 spawning 2 threads, each of them looping through push() and then pop(),
 and at one point, the call to pop() fails which should never fail.

 compilation line:

 {{{
 g++-4.6 -O1 -g -fno-inline -pthread -m64 -I/usr/local/include -c
 lockfree_test.cpp -o lockfree_test.cpp.o
 }}}


 sample program:

 {{{
 struct SemTask
 {
  int x;
 };
 boost::lockfree::queue<SemTask * > queue(1);

 void* runner(void* arg)
 {
     std::cout << '.' << std::endl;
     while (!t_exit)
     {
       SemTask * task = new SemTask();
       assert(queue.push(task));
       assert(queue.pop(task));
       delete task;
     }
     return NULL;
 }

 int main(int argc, char** argv)
 {
   assert(queue.is_lock_free());
   #define NUM_THRD 2
   pthread_t inc_x_thread[NUM_THRD];

   for (int i = 0; i < NUM_THRD; ++i) {
     if(pthread_create(&inc_x_thread[i], NULL, runner, NULL)) {
       fprintf(stderr, "Error creating thread\n");
       return -1;
     }
   }

   for (int i = 0; i < NUM_THRD; ++i) {
     if(pthread_join(inc_x_thread[i], NULL)) {
       fprintf(stderr, "Error joining thread\n");
       return -1;
     }
   }

   return 0;
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12394>
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