[src/trunk]: src/lib/libpthread add comments

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

details:   https://anonhg.NetBSD.org/src/rev/01b0abb6a63a
branches:  trunk
changeset: 785258:01b0abb6a63a
user:      yamt <yamt%NetBSD.org@localhost>
date:      Wed Mar 06 11:31:34 2013 +0000

description:
add comments
whitespace

diffstat:

 lib/libpthread/pthread_mutex.c |  22 +++++++++++++++++++---
 1 files changed, 19 insertions(+), 3 deletions(-)

diffs (64 lines):

diff -r f5a8cab3d02f -r 01b0abb6a63a lib/libpthread/pthread_mutex.c
--- a/lib/libpthread/pthread_mutex.c    Wed Mar 06 11:30:56 2013 +0000
+++ b/lib/libpthread/pthread_mutex.c    Wed Mar 06 11:31:34 2013 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pthread_mutex.c,v 1.54 2012/08/16 04:49:47 matt Exp $  */
+/*     $NetBSD: pthread_mutex.c,v 1.55 2013/03/06 11:31:34 yamt Exp $  */
 
 /*-
  * Copyright (c) 2001, 2003, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -47,7 +47,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: pthread_mutex.c,v 1.54 2012/08/16 04:49:47 matt Exp $");
+__RCSID("$NetBSD: pthread_mutex.c,v 1.55 2013/03/06 11:31:34 yamt Exp $");
 
 #include <sys/types.h>
 #include <sys/lwpctl.h>
@@ -130,7 +130,6 @@
        return 0;
 }
 
-
 int
 pthread_mutex_destroy(pthread_mutex_t *ptm)
 {
@@ -465,6 +464,12 @@
        return error;
 }
 
+/*
+ * pthread__mutex_wakeup: unpark threads waiting for us
+ *
+ * unpark threads on the ptm->ptm_waiters list and self->pt_waiters.
+ */
+
 static void
 pthread__mutex_wakeup(pthread_t self, pthread_mutex_t *ptm)
 {
@@ -530,6 +535,7 @@
                }
        }
 }
+
 int
 pthread_mutexattr_init(pthread_mutexattr_t *attr)
 {
@@ -578,6 +584,16 @@
        }
 }
 
+/*
+ * pthread__mutex_deferwake: try to defer unparking threads in self->pt_waiters
+ *
+ * In order to avoid unnecessary contention on the interlocking mutex,
+ * we defer waking up threads until we unlock the mutex.  The threads will
+ * be woken up when the calling thread (self) releases the first mutex with
+ * MUTEX_DEFERRED_BIT set.  It likely be the mutex 'ptm', but no problem
+ * even if it isn't.
+ */
+
 void
 pthread__mutex_deferwake(pthread_t self, pthread_mutex_t *ptm)
 {