From 4bace216b91c9f8244976305f462fd212b0e20c3 Mon Sep 17 00:00:00 2001
From: "Timothy A. Bish" <tabish@apache.org>
Date: Tue, 21 Aug 2012 23:28:50 +0000
Subject: [PATCH] updated fix: https://issues.apache.org/jira/browse/AMQ-3982

Instead of locking on the PList iterator which forces a lock on every access to hasNext we should lock down at the PageFile level in readPage making the seek and read an atomic operation.  Since many reads on a single already loaded page don't need to be synchronized we pay a higher price for locking in the specific PList case than we do buy creating this atomic read operation in PageFile.

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@1375852 13f79535-47bb-0310-9956-ffa450edef68
---
 .../apache/activemq/store/kahadb/plist/PList.java   |  4 +---
 .../main/java/org/apache/kahadb/page/PageFile.java  | 13 +++++++++++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/activemq-core/src/main/java/org/apache/activemq/store/kahadb/plist/PList.java b/activemq-core/src/main/java/org/apache/activemq/store/kahadb/plist/PList.java
index 09fbab2856..953be74cbd 100644
--- a/activemq-core/src/main/java/org/apache/activemq/store/kahadb/plist/PList.java
+++ b/activemq-core/src/main/java/org/apache/activemq/store/kahadb/plist/PList.java
@@ -202,9 +202,7 @@ public class PList extends ListIndex<String, Location> {
 
         @Override
         public boolean hasNext() {
-            synchronized (indexLock) {
-                return iterator.hasNext();
-            }
+            return iterator.hasNext();
         }
 
         @Override
diff --git a/kahadb/src/main/java/org/apache/kahadb/page/PageFile.java b/kahadb/src/main/java/org/apache/kahadb/page/PageFile.java
index 77dbf3c723..144cccb934 100644
--- a/kahadb/src/main/java/org/apache/kahadb/page/PageFile.java
+++ b/kahadb/src/main/java/org/apache/kahadb/page/PageFile.java
@@ -16,7 +16,16 @@
  */
 package org.apache.kahadb.page;
 
-import java.io.*;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.io.RandomAccessFile;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -862,7 +871,7 @@ public class PageFile {
         return nextTxid.incrementAndGet();
     }
 
-    void readPage(long pageId, byte[] data) throws IOException {
+    synchronized void readPage(long pageId, byte[] data) throws IOException {
         readFile.seek(toOffset(pageId));
         readFile.readFully(data);
     }