rewrite popen to use posix_spawn instead of fragile vfork hacks

[musl] / src / stdio / __lockfile.c

diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c
index 4e0239e..9d967d6 100644 (file)
--- a/src/stdio/__lockfile.c
+++ b/src/stdio/__lockfile.c
@@ -1,20 +1,28 @@
 #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);
 }