+ 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. */