From 0d47aa2d3aca0752f9913814457f1632e7df2bc6 Mon Sep 17 00:00:00 2001
From: Mark Riddoch <mriddoch@ks211278.kimsufi.com>
Date: Thu, 5 Sep 2013 22:05:55 +0200
Subject: [PATCH] Remove some contention on the DCB zombie queue spinlock

A fix for final free beign called when a DCB has not yet had a session created
---
 server/core/dcb.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/server/core/dcb.c b/server/core/dcb.c
index ec6b7553b..5723de960 100644
--- a/server/core/dcb.c
+++ b/server/core/dcb.c
@@ -161,6 +161,7 @@ dcb_add_to_zombieslist(DCB *dcb)
         if (dcb->state == DCB_STATE_ZOMBIE)
         {
                 ss_dassert(zombies != NULL);
+		spinlock_release(&zombiespin);
                 return;
         }
 
@@ -215,7 +216,7 @@ dcb_add_to_zombieslist(DCB *dcb)
 static void
 dcb_final_free(DCB *dcb)
 {
-SERVICE *service;
+SERVICE *service = NULL;
 
         CHK_DCB(dcb);
         ss_info_dassert(dcb->state == DCB_STATE_DISCONNECTED,
@@ -249,7 +250,8 @@ SERVICE *service;
         /**
          * Terminate router session.
          */
-        service = dcb->session->service;
+	if (dcb->session)
+	        service = dcb->session->service;
 
         if (service != NULL &&
             service->router != NULL &&
@@ -320,6 +322,16 @@ DCB*    dcb_list = NULL;
 DCB*    dcb = NULL;
 bool    succp = false;
 
+	/*
+	 * Perform a dirty read to see if there is anything in the queue.
+	 * This avoids threads hitting the queue spinlock when the queue 
+	 * is empty. This will really help when the only entry is being
+	 * freed, since the queue is updated before the expensive call to
+	 * dcb_final_free.
+	 */
+	if (!zombies)
+		return;
+
 	spinlock_acquire(&zombiespin);
 	ptr = zombies;
 	lptr = NULL;