From a37452430f93700aeb122d693959ad79d8e43ada Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Thu, 24 Mar 2011 23:16:52 -0400
Subject: [PATCH] simplify and optimize FILE lock handling

---
 src/internal/stdio_impl.h |  5 ++---
 src/stdio/__lockfile.c    | 13 +++++++------
 src/stdio/ftrylockfile.c  |  6 +++---
 src/stdio/vsnprintf.c     |  2 +-
 src/stdio/vswprintf.c     |  2 +-
 5 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
index 4e6d3503..b977df68 100644
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -23,8 +23,8 @@
 
 #define UNGET 4
 
-#define FLOCK(f) ((libc.lockfile && (f)->owner>=0) ? (libc.lockfile((f)),0) : 0)
-#define FUNLOCK(f) ((f)->lockcount && (--(f)->lockcount || ((f)->owner=(f)->lock=0)))
+#define FLOCK(f) ((libc.lockfile && (f)->lock>=0) ? (libc.lockfile((f)),0) : 0)
+#define FUNLOCK(f) ((f)->lockcount && (--(f)->lockcount || ((f)->lock=0)))
 
 #define F_PERM 1
 #define F_NORD 4
@@ -59,7 +59,6 @@ struct __FILE_s {
 	off_t (*seek)(FILE *, off_t, int);
 	int mode;
 	int (*close)(FILE *);
-	int owner;
 };
 
 size_t __stdio_read(FILE *, unsigned char *, size_t);
diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c
index e4320f05..93c94867 100644
--- a/src/stdio/__lockfile.c
+++ b/src/stdio/__lockfile.c
@@ -3,17 +3,18 @@
 
 void __lockfile(FILE *f)
 {
-	int spins;
-	if (f->owner < 0) return;
-	if (f->owner && f->owner == __pthread_self()->tid) {
+	int spins=100000;
+	int tid;
+
+	if (f->lock < 0) return;
+	tid = __pthread_self()->tid;
+	if (f->lock == tid) {
 		while (f->lockcount == INT_MAX);
 		f->lockcount++;
 		return;
 	}
-	spins = 100000;
-	while (a_swap(&f->lock, 1))
+	while (f->lock || a_cas(&f->lock, 0, tid))
 		if (spins) spins--, a_spin();
 		else syscall(SYS_sched_yield);
-	f->owner = __pthread_self()->tid;
 	f->lockcount = 1;
 }
diff --git a/src/stdio/ftrylockfile.c b/src/stdio/ftrylockfile.c
index 1d0a1ff8..67f4b6a0 100644
--- a/src/stdio/ftrylockfile.c
+++ b/src/stdio/ftrylockfile.c
@@ -3,16 +3,16 @@
 
 int ftrylockfile(FILE *f)
 {
+	int tid = pthread_self()->tid;
 	if (!libc.lockfile) libc.lockfile = __lockfile;
-	if (f->owner && f->owner == pthread_self()->tid) {
+	if (f->lock == tid) {
 		if (f->lockcount == INT_MAX)
 			return -1;
 		f->lockcount++;
 		return 0;
 	}
-	if (a_swap(&f->lock, 1))
+	if (f->lock || a_cas(&f->lock, 0, tid))
 		return -1;
-	f->owner = pthread_self()->tid;
 	f->lockcount = 1;
 	return 0;
 }
diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c
index ff792e17..5d3f0c5f 100644
--- a/src/stdio/vsnprintf.c
+++ b/src/stdio/vsnprintf.c
@@ -17,7 +17,7 @@ int vsnprintf(char *s, size_t n, const char *fmt, va_list ap)
 	f.write = sn_write;
 	f.buf_size = 1;
 	f.buf = buf;
-	f.owner = -1;
+	f.lock = -1;
 	if (n > INT_MAX) {
 		errno = EOVERFLOW;
 		return -1;
diff --git a/src/stdio/vswprintf.c b/src/stdio/vswprintf.c
index 4ad581fb..31ea1875 100644
--- a/src/stdio/vswprintf.c
+++ b/src/stdio/vswprintf.c
@@ -32,7 +32,7 @@ int vswprintf(wchar_t *s, size_t n, const wchar_t *fmt, va_list ap)
 	f.write = sw_write;
 	f.buf_size = sizeof buf;
 	f.buf = buf;
-	f.owner = -1;
+	f.lock = -1;
 	f.cookie = &c;
 	if (!n) {
 		return -1;
-- 
2.25.1