[src/trunk]: src/lib/libpthread Do a similar tuneup on pthread_cond_signal() and

[nathanw <nathanw%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/20b4a32d6f4e
branches:  trunk
changeset: 542504:20b4a32d6f4e
user:      nathanw <nathanw%NetBSD.org@localhost>
date:      Fri Jan 31 04:26:50 2003 +0000

description:
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.

diffstat:

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

diffs (75 lines):

diff -r f18600139ee7 -r 20b4a32d6f4e lib/libpthread/pthread_cond.c
--- a/lib/libpthread/pthread_cond.c     Fri Jan 31 02:55:00 2003 +0000
+++ b/lib/libpthread/pthread_cond.c     Fri Jan 31 04:26:50 2003 +0000
@@ -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 @@
 #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 @@
 #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;