From 69367db47f7df16bafa38e746d2264d8e1c3c124 Mon Sep 17 00:00:00 2001
From: nathanw <nathanw@NetBSD.org>
Date: Fri, 31 Jan 2003 04:26:50 +0000
Subject: [PATCH] Do a similar tuneup on pthread_cond_signal() and
 pthread_cond_broadcast(): use double-checked locking to avoid pthread__self()
 and pthread_spinlock() when signaling or broadcasting on a condition variable
 with no waiters.

---
 lib/libpthread/pthread_cond.c | 46 +++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/lib/libpthread/pthread_cond.c b/lib/libpthread/pthread_cond.c
index 72805ec2fe95..be083e829303 100644
--- a/lib/libpthread/pthread_cond.c
+++ b/lib/libpthread/pthread_cond.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: pthread_cond.c,v 1.3 2003/01/27 21:01:01 nathanw Exp $	*/
+/*	$NetBSD: pthread_cond.c,v 1.4 2003/01/31 04:26:50 nathanw Exp $	*/
 
 /*-
  * Copyright (c) 2001 The NetBSD Foundation, Inc.
@@ -267,21 +267,23 @@ pthread_cond_signal(pthread_cond_t *cond)
 #endif
 	PTHREADD_ADD(PTHREADD_COND_SIGNAL);
 
-	self = pthread__self();
 	SDPRINTF(("(cond signal %p) Signaling %p\n",
-	    self, cond));
+	    pthread__self(), cond));
 
-	pthread_spinlock(self, &cond->ptc_lock);
-	signaled = PTQ_FIRST(&cond->ptc_waiters);
-	if (signaled != NULL)
-		PTQ_REMOVE(&cond->ptc_waiters, signaled, pt_sleep);
+	if (!PTQ_EMPTY(&cond->ptc_waiters)) {
+		self = pthread__self();
+		pthread_spinlock(self, &cond->ptc_lock);
+		signaled = PTQ_FIRST(&cond->ptc_waiters);
+		if (signaled != NULL)
+			PTQ_REMOVE(&cond->ptc_waiters, signaled, pt_sleep);
 #ifdef ERRORCHECK
-	if (PTQ_EMPTY(&cond->ptc_waiters))
-		cond->ptc_mutex = NULL;
+		if (PTQ_EMPTY(&cond->ptc_waiters))
+			cond->ptc_mutex = NULL;
 #endif
-	if (signaled != NULL)
-		pthread__sched(self, signaled);
-	pthread_spinunlock(self, &cond->ptc_lock);
+		if (signaled != NULL)
+			pthread__sched(self, signaled);
+		pthread_spinunlock(self, &cond->ptc_lock);
+	}
 
 	return 0;
 }
@@ -298,19 +300,21 @@ pthread_cond_broadcast(pthread_cond_t *cond)
 #endif
 
 	PTHREADD_ADD(PTHREADD_COND_BROADCAST);
-	self = pthread__self();
 	SDPRINTF(("(cond signal %p) Broadcasting %p\n",
-	    self, cond));
+	    pthread__self(), cond));
 
-	pthread_spinlock(self, &cond->ptc_lock);
-	blockedq = cond->ptc_waiters;
-	PTQ_INIT(&cond->ptc_waiters);
+	if (!PTQ_EMPTY(&cond->ptc_waiters)) {
+		self = pthread__self();
+		pthread_spinlock(self, &cond->ptc_lock);
+		blockedq = cond->ptc_waiters;
+		PTQ_INIT(&cond->ptc_waiters);
 #ifdef ERRORCHECK
-	cond->ptc_mutex = NULL;
+		cond->ptc_mutex = NULL;
 #endif
-	PTQ_FOREACH(signaled, &blockedq, pt_sleep)
-	    pthread__sched(self, signaled);
-	pthread_spinunlock(self, &cond->ptc_lock);
+		PTQ_FOREACH(signaled, &blockedq, pt_sleep)
+		    pthread__sched(self, signaled);
+		pthread_spinunlock(self, &cond->ptc_lock);
+	}
 
 	return 0;