From 2768eef1dc34f6496eeaa4781308792c00276a35 Mon Sep 17 00:00:00 2001
From: Jay J Wylie <jay.j.wylie@gmail.com>
Date: Thu, 8 Nov 2012 14:48:38 -0800
Subject: [PATCH] Changed reset and destroyRequestQueue to avoid any heavy
 weight synchronization methods. This should fix deadlock issue.

---
 .../utils/pool/QueuedKeyedResourcePool.java   | 23 ++++++++++++-------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/java/voldemort/utils/pool/QueuedKeyedResourcePool.java b/src/java/voldemort/utils/pool/QueuedKeyedResourcePool.java
index e545019ce1..9c5cdc7bd2 100644
--- a/src/java/voldemort/utils/pool/QueuedKeyedResourcePool.java
+++ b/src/java/voldemort/utils/pool/QueuedKeyedResourcePool.java
@@ -243,11 +243,13 @@ protected void destroyRequest(AsyncResourceRequest<V> resourceRequest) {
      * @param requestQueue The queue for which all resource requests are to be
      *        destroyed.
      */
-    private synchronized void destroyRequestQueue(Queue<AsyncResourceRequest<V>> requestQueue) {
-        AsyncResourceRequest<V> resourceRequest = requestQueue.poll();
-        while(resourceRequest != null) {
-            destroyRequest(resourceRequest);
-            resourceRequest = requestQueue.poll();
+    private void destroyRequestQueue(Queue<AsyncResourceRequest<V>> requestQueue) {
+        if(requestQueue != null) {
+            AsyncResourceRequest<V> resourceRequest = requestQueue.poll();
+            while(resourceRequest != null) {
+                destroyRequest(resourceRequest);
+                resourceRequest = requestQueue.poll();
+            }
         }
     }
 
@@ -283,9 +285,14 @@ public void close() {
     @Override
     public void reset(K key) {
         // First, destroy enqueued resource requests (if any exist).
-        Queue<AsyncResourceRequest<V>> requestQueue = requestQueueMap.get(key);
-        if(requestQueue != null) {
-            destroyRequestQueue(requestQueue);
+        Queue<AsyncResourceRequest<V>> requestQueueToDestroy = requestQueueMap.get(key);
+        if(requestQueueToDestroy != null) {
+            // Swap in a new requestQueue so that the current requestQueue can
+            // be destroyed without the need of any synchronization primitives
+            Queue<AsyncResourceRequest<V>> newRequestQueue = new ConcurrentLinkedQueue<AsyncResourceRequest<V>>();
+            if(requestQueueMap.replace(key, requestQueueToDestroy, newRequestQueue)) {
+                destroyRequestQueue(requestQueueToDestroy);
+            }
         }
 
         // Second, destroy resources in the pool.