#include "stdio_impl.h"
#include "pthread_impl.h"
-void __lockfile(FILE *f)
+int __lockfile(FILE *f)
{
- int spins=100000;
- int tid;
+ int owner, tid = __pthread_self()->tid;
+ if (f->lock == tid)
+ return 0;
+ while ((owner = a_cas(&f->lock, 0, tid)))
+ __wait(&f->lock, &f->waiters, 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->lock < 0) return;
- tid = __pthread_self()->tid;
- if (f->lock == tid) {
- while (f->lockcount == INT_MAX);
- f->lockcount++;
- return;
- }
- while (a_cas(&f->lock, 0, tid))
- if (spins) spins--, a_spin();
- else syscall(SYS_sched_yield);
- f->lockcount = 1;
+ if (f->waiters) __wake(&f->lock, 1, 1);
}