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);
+ owner = a_cas(&f->lock, 0, tid);
+ if (!owner) return 1;
+ while ((owner = a_cas(&f->lock, 0, tid|MAYBE_WAITERS))) {
+ if ((owner & MAYBE_WAITERS) ||
+ a_cas(&f->lock, owner, owner|MAYBE_WAITERS)==owner)
+ __futexwait(&f->lock, owner|MAYBE_WAITERS, 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);
}