GNU bug report logs - #6729
[PATCH] sort: omit unnecessary mutex unlock+lock; simplify heap access

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From: Paul Eggert <eggert <at> CS.UCLA.EDU>
To: 6729 <at> debbugs.gnu.org
Subject: bug#6729: [PATCH] sort: omit unnecessary mutex unlock+lock; simplify heap access
Date: Sun, 25 Jul 2010 20:57:24 -0700

This removes an unnecessary mutex lock+unlock
and prepares for a refactoring patch to heap.c that I'll
install shortly.

From 7cc2429f13db9b0b70572ac1879506f4e444f4c6 Mon Sep 17 00:00:00 2001
From: Paul R. Eggert <eggert <at> cs.ucla.edu>
Date: Sun, 25 Jul 2010 20:54:55 -0700
Subject: [PATCH] sort: omit unnecessary mutex unlock+lock; simplify heap access

* src/sort.c (queue_pop): Omit unnecessary unlock+lock after
pthread_cond_wait returns.  Don't access "count" member of the
heap; any efficiency gains should be quite minor, the access
complicates this code, and "count" should be private anyway.
---
 src/sort.c |   19 +++++--------------
 1 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/src/sort.c b/src/sort.c
index ea2720f..577521d 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -3173,20 +3173,11 @@ queue_insert (struct merge_node_queue *queue, struct merge_node *node)
 static inline struct merge_node *
 queue_pop (struct merge_node_queue *queue)
 {
-  struct merge_node *node = NULL;
-
-  while (!node)
-    {
-      pthread_mutex_lock (&queue->mutex);
-      if (queue->priority_queue->count)
-        node = heap_remove_top (queue->priority_queue);
-      else
-        {
-          /* Go into conditional wait if no NODE is immediately available.  */
-          pthread_cond_wait (&queue->cond, &queue->mutex);
-        }
-      pthread_mutex_unlock (&queue->mutex);
-    }
+  struct merge_node *node;
+  pthread_mutex_lock (&queue->mutex);
+  while (! (node = heap_remove_top (queue->priority_queue)))
+    pthread_cond_wait (&queue->cond, &queue->mutex);
+  pthread_mutex_unlock (&queue->mutex);
   lock_node (node);
   node->queued = false;
   return node;
-- 
1.7.1

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