diff options
Diffstat (limited to 'src/stdio/__lockfile.c')
| -rw-r--r-- | src/stdio/__lockfile.c | 29 |
1 files changed, 13 insertions, 16 deletions
diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c index 9d967d6e..2ff75d8a 100644 --- a/src/stdio/__lockfile.c +++ b/src/stdio/__lockfile.c @@ -1,28 +1,25 @@ #include "stdio_impl.h" #include "pthread_impl.h" +#define MAYBE_WAITERS 0x40000000 + int __lockfile(FILE *f) { - int owner, tid = __pthread_self()->tid; - if (f->lock == tid) + int owner = f->lock, tid = __pthread_self()->tid; + if ((owner & ~MAYBE_WAITERS) == tid) return 0; - while ((owner = a_cas(&f->lock, 0, tid))) - __wait(&f->lock, &f->waiters, owner, 1); + for (;;) { + owner = a_cas(&f->lock, 0, tid); + if (!owner) return 1; + if (a_cas(&f->lock, owner, owner|MAYBE_WAITERS)==owner) break; + } + while ((owner = a_cas(&f->lock, 0, tid|MAYBE_WAITERS))) + __futexwait(&f->lock, owner, 1); return 1; } void __unlockfile(FILE *f) { - a_store(&f->lock, 0); - - /* The following read is technically invalid under situations - * of self-synchronized destruction. Another thread may have - * called fclose as soon as the above store has completed. - * Nonetheless, since FILE objects always live in memory - * obtained by malloc from the heap, it's safe to assume - * the dereferences below will not fault. In the worst case, - * a spurious syscall will be made. If the implementation of - * malloc changes, this assumption needs revisiting. */ - - if (f->waiters) __wake(&f->lock, 1, 1); + if (a_swap(&f->lock, 0) & MAYBE_WAITERS) + __wake(&f->lock, 1, 1); } |