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: simplify and optimize FILE lock handling

---
 src/stdio/__lockfile.c   | 13 +++++++------
 src/stdio/ftrylockfile.c |  6 +++---
 src/stdio/vsnprintf.c    |  2 +-
 src/stdio/vswprintf.c    |  2 +-
 4 files changed, 12 insertions(+), 11 deletions(-)

(limited to 'src/stdio')

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;
-- 
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