HDFS-5239. Allow FSNamesystem lock fairness to be configurable. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1533252 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -24,6 +24,9 @@ Release 0.23.10 - UNRELEASED
 
   OPTIMIZATIONS
 
+    HDFS-5239.  Allow FSNamesystem lock fairness to be configurable (daryn via
+    kihwal)
+
   BUG FIXES
 
     HDFS-4984. Incorrect Quota counting in INodeFile. (jing9 via kihwal)

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

@@ -350,7 +350,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
     this.systemStart = now();
     this.blockManager = new BlockManager(this, this, conf);
     this.datanodeStatistics = blockManager.getDatanodeManager().getDatanodeStatistics();
-    this.fsLock = new ReentrantReadWriteLock(true); // fair locking
+    this.fsLock = createFsLock(conf);
     setConfigurationParameters(conf);
     // For testing purposes, allow the DT secret manager to be started regardless
     // of whether security is enabled.
@@ -373,6 +373,12 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
     this.safeMode = new SafeModeInfo(conf);
   }
 
+  private static ReentrantReadWriteLock createFsLock(Configuration conf) {
+    boolean fair = conf.getBoolean("dfs.namenode.fslock.fair", true);
+    LOG.info("fsLock is fair:" + fair);
+    return new ReentrantReadWriteLock(fair);
+  }
+
   void activateSecretManager() throws IOException {
     if (dtSecretManager != null) {
       dtSecretManager.startThreads();
@@ -472,7 +478,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
    * is stored
    */
   FSNamesystem(FSImage fsImage, Configuration conf) throws IOException {
-    this.fsLock = new ReentrantReadWriteLock(true);
+    this.fsLock = createFsLock(conf);
     this.blockManager = new BlockManager(this, this, conf);
     setConfigurationParameters(conf);
     this.dir = new FSDirectory(fsImage, this, conf);
@@ -4548,4 +4554,14 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
   public SafeModeInfo getSafeModeInfoForTests() {
     return safeMode;
   }
+  
+  @VisibleForTesting
+  void setFsLockForTests(ReentrantReadWriteLock lock) {
+    this.fsLock = lock;
+  }
+  
+  @VisibleForTesting
+  ReentrantReadWriteLock getFsLockForTests() {
+    return fsLock;
+  }
 }

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

@@ -18,7 +18,7 @@
 
 package org.apache.hadoop.hdfs.server.namenode;
 
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 import java.io.IOException;
 
@@ -72,4 +72,21 @@ 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(fsImage, conf);
+    assertTrue(fsNamesystem.getFsLockForTests().isFair());
+    
+    conf.setBoolean("dfs.namenode.fslock.fair", false);
+    fsNamesystem = new FSNamesystem(fsImage, conf);
+    assertFalse(fsNamesystem.getFsLockForTests().isFair());
+  }  
 }