src/thread/pthread_once.c

   1 #include "pthread_impl.h"
   2
   3 static void undo(void *control)
   4 {
   5         a_store(control, 0);
   6         __wake(control, 1, 0);
   7 }
   8
   9 int pthread_once(pthread_once_t *control, void (*init)(void))
  10 {
  11         static int waiters;
  12
  13         /* Return immediately if init finished before */
  14         if (*control == 2) return 0;
  15
  16         /* Try to enter initializing state. Three possibilities:
  17          *  0 - we're the first or the other cancelled; run init
  18          *  1 - another thread is running init; wait
  19          *  2 - another thread finished running init; just return */
  20
  21         for (;;) switch (a_swap(control, 1)) {
  22         case 0:
  23                 pthread_cleanup_push(undo, control);
  24                 init();
  25                 pthread_cleanup_pop(0);
  26
  27                 a_store(control, 2);
  28                 if (waiters) __wake(control, -1, 0);
  29                 return 0;
  30         case 1:
  31                 __wait(control, &waiters, 1, 0);
  32                 continue;
  33         case 2:
  34                 a_store(control, 2);
  35                 return 0;
  36         }
  37 }