svn commit: r1533191 - /hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java

[liyin]

Author: liyin
Date: Thu Oct 17 18:18:20 2013
New Revision: 1533191

URL: http://svn.apache.org/r1533191
Log:
[HBASE-6371] [0.89-fb] BugFix: concurrency problem, was locking on an Integer 
created by auto-boxing ; now uses a lock-free integer (AtomicLong) to avoid 
locking and concurrency issues.

Author: jmarg

Summary: BugFix: concurrency problem, was locking on an Integer created by 
auto-boxing ; now uses a lock-free integer (AtomicLong) to avoid locking and 
concurrency issues.

Test Plan:
Run the test suite of HBase using maven:
  $ mvn test

Reviewers: aaiyer, manukranthk

Reviewed By: aaiyer

CC: san, rongrong

Differential Revision: https://phabricator.fb.com/D1014395

Task ID: 3008730

Modified:
    
hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java

Modified: 
hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java
URL: 
http://svn.apache.org/viewvc/hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java?rev=1533191&r1=1533190&r2=1533191&view=diff
==============================================================================
--- 
hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java
 (original)
+++ 
hbase/branches/0.89-fb/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSelection.java
 Thu Oct 17 18:18:20 2013
@@ -18,10 +18,21 @@
  * limitations under the License.
  */
 
+/**
+ * This class is NOT thread-safe.
+ *
+ * It does support concurrent access by multiple threads only if each object
+ * is accessed by only one thread.
+ *
+ * The synchronisation is done so that the static fields of the class are
+ * consistents.
+ */
+
 package org.apache.hadoop.hbase.regionserver;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicLong;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -42,7 +53,7 @@ public class CompactSelection {
   List<StoreFile> filesToCompact = new ArrayList<StoreFile>();
   // number of off peak compactions either in the compaction queue or  
   // happening now
-  public static Integer numOutstandingOffPeakCompactions = 0;
+  private static AtomicLong numOutstandingOffPeakCompactions = new 
AtomicLong(0);
   // was this compaction promoted to an off-peak
   boolean isOffPeakCompaction = false;
   // Remember the set of expired storeFiles
@@ -70,13 +81,11 @@ public class CompactSelection {
    */
   public void finishRequest() {
     if (isOffPeakCompaction) {
-      synchronized(numOutstandingOffPeakCompactions) {
-        numOutstandingOffPeakCompactions--;
-        isOffPeakCompaction = false;
-      }
-      LOG.info("Compaction done, numOutstandingOffPeakCompactions is now " + 
-          numOutstandingOffPeakCompactions);
+      numOutstandingOffPeakCompactions.decrementAndGet();
+      isOffPeakCompaction = false;
     }
+    LOG.info("Compaction done, numOutstandingOffPeakCompactions is now " +
+        numOutstandingOffPeakCompactions.get());
   }
   
   public List<StoreFile> getFilesToCompact() {
@@ -90,14 +99,12 @@ public class CompactSelection {
   public void emptyFileList() {
     filesToCompact.clear();
     if (isOffPeakCompaction) {
-      synchronized(numOutstandingOffPeakCompactions) {
-        // reset the off peak count
-        numOutstandingOffPeakCompactions--;
-        isOffPeakCompaction = false;
-      }
-      LOG.info("Nothing to compact, numOutstandingOffPeakCompactions is now " 
+ 
-          numOutstandingOffPeakCompactions);
+      // reset the off peak count
+      numOutstandingOffPeakCompactions.decrementAndGet();
+      isOffPeakCompaction = false;
     }
+    LOG.info("Nothing to compact, numOutstandingOffPeakCompactions is now " +
+        numOutstandingOffPeakCompactions.get());
   }
   
   public boolean isOffPeakCompaction() {
@@ -105,16 +112,12 @@ public class CompactSelection {
   }
 
   void setOffPeak() {
-    synchronized (numOutstandingOffPeakCompactions) {
-      numOutstandingOffPeakCompactions++;
-      isOffPeakCompaction = true;
-    }
+    numOutstandingOffPeakCompactions.incrementAndGet();
+    isOffPeakCompaction = true;
   }
 
- static int getNumOutStandingOffPeakCompactions() {
-   synchronized(numOutstandingOffPeakCompactions) {
-    return numOutstandingOffPeakCompactions;
-   }
+ static long getNumOutStandingOffPeakCompactions() {
+   return numOutstandingOffPeakCompactions.get();
  }
   
   public CompactSelection subList(int start, int end) {