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#include "stdio_impl.h" #include "pthread_impl.h" int __lockfile(FILE *f) { 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->waiters) __wake(&f->lock, 1, 1); } |