merge -c 1525624 FIXES: HDFS-5239. Allow FSNamesystem lock fairness to be configurable (daryn)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1525625 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -50,6 +50,8 @@ Release 2.3.0 - UNRELEASED
 
   OPTIMIZATIONS
 
+    HDFS-5239.  Allow FSNamesystem lock fairness to be configurable (daryn)
+
   BUG FIXES
     HDFS-5034.  Remove debug prints from GetFileLinkInfo (Andrew Wang via Colin
     Patrick McCabe)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -420,7 +420,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
   private final long accessTimePrecision;
 
   /** Lock to protect FSNamesystem. */
-  private ReentrantReadWriteLock fsLock = new ReentrantReadWriteLock(true);
+  private ReentrantReadWriteLock fsLock;
 
   /**
    * Used when this NN is in standby state to read from the shared edit log.
@@ -595,6 +595,9 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
    */
   FSNamesystem(Configuration conf, FSImage fsImage, boolean ignoreRetryCache)
       throws IOException {
+    boolean fair = conf.getBoolean("dfs.namenode.fslock.fair", true);
+    LOG.info("fsLock is fair:" + fair);
+    fsLock = new ReentrantReadWriteLock(fair);
     try {
       resourceRecheckInterval = conf.getLong(
           DFS_NAMENODE_RESOURCE_CHECK_INTERVAL_KEY,

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystem.java

@@ -20,8 +20,7 @@ package org.apache.hadoop.hdfs.server.namenode;
 
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_EDITS_DIR_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 import java.io.File;
 import java.io.IOException;
@@ -142,4 +141,21 @@ public class TestFSNamesystem {
     assertTrue("Replication queues weren't being populated after entering "
       + "safemode 2nd time", fsn.isPopulatingReplQueues());
   }
+  
+  @Test
+  public void testFsLockFairness() throws IOException, InterruptedException{
+    Configuration conf = new Configuration();
+
+    FSEditLog fsEditLog = Mockito.mock(FSEditLog.class);
+    FSImage fsImage = Mockito.mock(FSImage.class);
+    Mockito.when(fsImage.getEditLog()).thenReturn(fsEditLog);
+
+    conf.setBoolean("dfs.namenode.fslock.fair", true);
+    FSNamesystem fsNamesystem = new FSNamesystem(conf, fsImage);
+    assertTrue(fsNamesystem.getFsLockForTests().isFair());
+    
+    conf.setBoolean("dfs.namenode.fslock.fair", false);
+    fsNamesystem = new FSNamesystem(conf, fsImage);
+    assertFalse(fsNamesystem.getFsLockForTests().isFair());
+  }  
 }