nsz Git - musl/blob - src/stdio/__lockfile.c

   1 #include "stdio_impl.h"
   2 #include "pthread_impl.h"
   3
   4 #define MAYBE_WAITERS 0x40000000
   5
   6 int __lockfile(FILE *f)
   7 {
   8         int owner = f->lock, tid = __pthread_self()->tid;
   9         if ((owner & ~MAYBE_WAITERS) == tid)
  10                 return 0;
  11         for (;;) {
  12                 owner = a_cas(&f->lock, 0, tid);
  13                 if (!owner) return 1;
  14                 if (a_cas(&f->lock, owner, owner|MAYBE_WAITERS)==owner) break;
  15         }
  16         while ((owner = a_cas(&f->lock, 0, tid|MAYBE_WAITERS)))
  17                 __futexwait(&f->lock, owner, 1);
  18         return 1;
  19 }
  20
  21 void __unlockfile(FILE *f)
  22 {
  23         if (a_swap(&f->lock, 0) & MAYBE_WAITERS)
  24                 __wake(&f->lock, 1, 1);
  25 }