From 15bf5db9c7ee5f48ba5b5c35af24f51cba23b92c Mon Sep 17 00:00:00 2001
From: Alan Bateman <alanb@openjdk.org>
Date: Thu, 2 Apr 2009 11:19:34 +0100
Subject: [PATCH] 6666739: (ref) ReferenceQueue.poll() doesn't scale well
 6711667: (ref) Update SoftReference timestamp only if clock advances

Forward port from 6u14; originally fixed by Tom Rodriguez in earlier update

Reviewed-by: martin
---
 jdk/src/share/classes/java/lang/ref/ReferenceQueue.java | 4 +++-
 jdk/src/share/classes/java/lang/ref/SoftReference.java  | 9 ++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java b/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java
index 872ee14f8e2..9882844e5a8 100644
--- a/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java
+++ b/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java
@@ -51,7 +51,7 @@ public class ReferenceQueue<T> {
 
     static private class Lock { };
     private Lock lock = new Lock();
-    private Reference<? extends T> head = null;
+    private volatile Reference<? extends T> head = null;
     private long queueLength = 0;
 
     boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
@@ -95,6 +95,8 @@ public class ReferenceQueue<T> {
      *          otherwise <code>null</code>
      */
     public Reference<? extends T> poll() {
+        if (head == null)
+            return null;
         synchronized (lock) {
             return reallyPoll();
         }
diff --git a/jdk/src/share/classes/java/lang/ref/SoftReference.java b/jdk/src/share/classes/java/lang/ref/SoftReference.java
index 35c6710d18e..4a6428efaf4 100644
--- a/jdk/src/share/classes/java/lang/ref/SoftReference.java
+++ b/jdk/src/share/classes/java/lang/ref/SoftReference.java
@@ -63,11 +63,13 @@ package java.lang.ref;
 
 public class SoftReference<T> extends Reference<T> {
 
-    /* Timestamp clock, updated by the garbage collector
+    /**
+     * Timestamp clock, updated by the garbage collector
      */
     static private long clock;
 
-    /* Timestamp updated by each invocation of the get method.  The VM may use
+    /**
+     * Timestamp updated by each invocation of the get method.  The VM may use
      * this field when selecting soft references to be cleared, but it is not
      * required to do so.
      */
@@ -108,7 +110,8 @@ public class SoftReference<T> extends Reference<T> {
      */
     public T get() {
         T o = super.get();
-        if (o != null) this.timestamp = clock;
+        if (o != null && this.timestamp != clock)
+            this.timestamp = clock;
         return o;
     }