Olivier Langlois's blog

I have done pthread programming for a while and read a couple of books on the topic too but nothing have prepared me to the undefined behavior that I have discovered the hard way.

The POSIX standard states that when the main thread exits the process, the remaining threads will be automatically terminated. What the standard does not specify is in which order the different process cleanup will occur hence if you leave the process without terminating yourself the threads, you will get undefined behavior. In my case, it was a segmentation fault.

The undefined behavior is real especially if this is a C++ program because part of the termination cleanup, there is the destruction of the program global objects. If your threads are still running and happen to use global objects, this is a sure way to a segmentation fault.

Even in fixing the problem, I have learned again something new about pthreads programming. To fix my problem, I just sent to myself the SIGINT signal that initiates the correct termination. In my first attempt, I have replaced my exit() function call with raise(SIGINT) which I have read in my UNIX programming textbook was the equivalent to kill(getpid(), SIGINT) but by doing so, the signal was never received. After some investigation, I have found in a book, that in a multithread program, raise(SIGINT) was equivalent to pthread_kill(pthread_self(),SIGINT). In my case, calling raise was doing nothing because the signal was blocked in the thread from where the call was done. Everything finally worked fine when I replaced the raise call with kill(getpid(), SIGINT).