HDDS-1830 OzoneManagerDoubleBuffer#stop should wait for daemon thread to die (#1156)

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/ratis/OzoneManagerDoubleBuffer.java

@@ -21,6 +21,7 @@ package org.apache.hadoop.ozone.om.ratis;
 import java.io.IOException;
 import java.util.Queue;
 import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 
 import com.google.common.annotations.VisibleForTesting;
@@ -64,7 +65,7 @@ public class OzoneManagerDoubleBuffer {
   private final OMMetadataManager omMetadataManager;
   private final AtomicLong flushedTransactionCount = new AtomicLong(0);
   private final AtomicLong flushIterations = new AtomicLong(0);
-  private volatile boolean isRunning;
+  private final AtomicBoolean isRunning = new AtomicBoolean(false);
   private OzoneManagerDoubleBufferMetrics ozoneManagerDoubleBufferMetrics;
   private long maxFlushedTransactionsInOneIteration;
 
@@ -79,7 +80,7 @@ public class OzoneManagerDoubleBuffer {
     this.ozoneManagerDoubleBufferMetrics =
         OzoneManagerDoubleBufferMetrics.create();
 
-    isRunning = true;
+    isRunning.set(true);
     // Daemon thread which runs in back ground and flushes transactions to DB.
     daemon = new Daemon(this::flushTransactions);
     daemon.setName("OMDoubleBufferFlushThread");
@@ -92,7 +93,7 @@ public class OzoneManagerDoubleBuffer {
    * and commit to DB.
    */
   private void flushTransactions() {
-    while(isRunning) {
+    while (isRunning.get()) {
       try {
         if (canFlush()) {
           setReadyBuffer();
@@ -140,7 +141,7 @@ public class OzoneManagerDoubleBuffer {
         }
       } catch (InterruptedException ex) {
         Thread.currentThread().interrupt();
-        if (isRunning) {
+        if (isRunning.get()) {
           final String message = "OMDoubleBuffer flush thread " +
               Thread.currentThread().getName() + " encountered Interrupted " +
               "exception while running";
@@ -201,11 +202,16 @@ public class OzoneManagerDoubleBuffer {
   /**
    * Stop OM DoubleBuffer flush thread.
    */
-  public synchronized void stop() {
-    if (isRunning) {
+  public void stop() {
+    if (isRunning.compareAndSet(true, false)) {
       LOG.info("Stopping OMDoubleBuffer flush thread");
-      isRunning = false;
       daemon.interrupt();
+      try {
+        // Wait for daemon thread to exit
+        daemon.join();
+      } catch (InterruptedException e) {
+        LOG.error("Interrupted while waiting for daemon to exit.");
+      }
 
       // stop metrics.
       ozoneManagerDoubleBufferMetrics.unRegister();