--- /dev/null
+#include "stdio_impl.h"
+#include "pthread_impl.h"
+
+#ifdef __GNUC__
+__attribute__((__noinline__))
+#endif
+static int locking_putc(int c, FILE *f, int tid)
+{
+ if (a_cas(&f->lock, 0, tid)) __lockfile(f);
+ c = putc_unlocked(c, f);
+ if (a_swap(&f->lock, 0) & MAYBE_WAITERS)
+ __wake(&f->lock, 1, 1);
+ return c;
+}
+
+static inline int do_putc(int c, FILE *f)
+{
+ int tid, l = f->lock;
+ if (l < 0 || (l & ~MAYBE_WAITERS) == (tid=__pthread_self()->tid))
+ return putc_unlocked(c, f);
+ return locking_putc(c, f, tid);
+}