Ways to Find a Race Condition

Question

I have a bit of code with a race condition in it... I know that it is a race condition because it does not happen consistently, and it seems to happen more often on dual core ma

Answer 1

There is a tool included in CLang and gcc 4.8+ called ThreadSanitizer.

You compile your code using the -fsanitize=thread flag

Example:

$ cat simple_race.cc
#include 
#include 

int Global;

void *Thread1(void *x) {
  Global++;
  return NULL;
}

void *Thread2(void *x) {
  Global--;
  return NULL;
}

int main() {
  pthread_t t[2];
  pthread_create(&t[0], NULL, Thread1, NULL);
  pthread_create(&t[1], NULL, Thread2, NULL);
  pthread_join(t[0], NULL);
  pthread_join(t[1], NULL);
}

And the output

$ clang++ simple_race.cc -fsanitize=thread -fPIE -pie -g
$ ./a.out 
==================
WARNING: ThreadSanitizer: data race (pid=26327)
  Write of size 4 at 0x7f89554701d0 by thread T1:
    #0 Thread1(void*) simple_race.cc:8 (exe+0x000000006e66)

  Previous write of size 4 at 0x7f89554701d0 by thread T2:
    #0 Thread2(void*) simple_race.cc:13 (exe+0x000000006ed6)

  Thread T1 (tid=26328, running) created at:
    #0 pthread_create tsan_interceptors.cc:683 (exe+0x00000001108b)
    #1 main simple_race.cc:19 (exe+0x000000006f39)

  Thread T2 (tid=26329, running) created at:
    #0 pthread_create tsan_interceptors.cc:683 (exe+0x00000001108b)
    #1 main simple_race.cc:20 (exe+0x000000006f63)
==================
ThreadSanitizer: reported 1 warnings