WARNING: ThreadSanitizer: data race (pid=9337)
  Write of size 4 at 0x7fe3c3075190 by thread T1:
    #0 foo2() simple_stack2.cc:20 (exe+0x000000003d0c)
    #1 bar2() simple_stack2.cc:29 (exe+0x000000003d74)
    #2 main simple_stack2.cc:41 (exe+0x000000003ddb)

  Previous read of size 4 at 0x7fe3c3075190 by main thread:
    #0 foo1() simple_stack2.cc:9 (exe+0x000000003c9a)
    #1 bar1() simple_stack2.cc:16 (exe+0x000000003ce4)
    #2 Thread1(void*) simple_stack2.cc:34 (exe+0x000000003d99)

  Thread T1 (tid=9338, running) created at:
    #0 pthread_create tsan_interceptors.cc:683 (exe+0x00000000de83)
    #1 main simple_stack2.cc:40 (exe+0x000000003dd6)
