HDFS-14258. Introduce Java Concurrent Package To DataXceiverServer Class. Contributed by BELUGA BEHR.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -581,7 +581,15 @@ public class DataNode extends ReconfigurableBase
                       "balancer max concurrent movers must be larger than 0"));
             }
           }
-          xserver.updateBalancerMaxConcurrentMovers(movers);
+          boolean success = xserver.updateBalancerMaxConcurrentMovers(movers);
+          if (!success) {
+            rootException = new ReconfigurationException(
+                property,
+                newVal,
+                getConf().get(property),
+                new IllegalArgumentException(
+                    "Could not modify concurrent moves thread count"));
+          }
           return Integer.toString(movers);
         } catch (NumberFormatException nfe) {
           rootException = new ReconfigurationException(

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataXceiverServer.java

@@ -21,35 +21,48 @@ import java.io.IOException;
 import java.net.SocketTimeoutException;
 import java.nio.channels.AsynchronousCloseException;
 import java.util.HashMap;
-import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.Semaphore;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
+import org.apache.commons.io.IOUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.net.Peer;
 import org.apache.hadoop.hdfs.net.PeerServer;
 import org.apache.hadoop.hdfs.util.DataTransferThrottler;
-import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.util.Daemon;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
 
 import org.slf4j.Logger;
 
 /**
- * Server used for receiving/sending a block of data.
- * This is created to listen for requests from clients or 
- * other DataNodes.  This small server does not use the 
- * Hadoop IPC mechanism.
+ * Server used for receiving/sending a block of data. This is created to listen
+ * for requests from clients or other DataNodes. This small server does not use
+ * the Hadoop IPC mechanism.
  */
 class DataXceiverServer implements Runnable {
   public static final Logger LOG = DataNode.LOG;
-  
+
+  /**
+   * Default time to wait (in seconds) for the number of running threads to drop
+   * below the newly requested maximum before giving up.
+   */
+  private static final int DEFAULT_RECONFIGURE_WAIT = 30;
+
   private final PeerServer peerServer;
   private final DataNode datanode;
-  private final HashMap<Peer, Thread> peers = new HashMap<Peer, Thread>();
-  private final HashMap<Peer, DataXceiver> peersXceiver = new HashMap<Peer, DataXceiver>();
+  private final HashMap<Peer, Thread> peers = new HashMap<>();
+  private final HashMap<Peer, DataXceiver> peersXceiver = new HashMap<>();
+  private final Lock lock = new ReentrantLock();
+  private final Condition noPeers = lock.newCondition();
   private boolean closed = false;
-  
+  private int maxReconfigureWaitTime = DEFAULT_RECONFIGURE_WAIT;
+
   /**
    * Maximal number of concurrent xceivers per node.
    * Enforcing the limit is required in order to avoid data-node
@@ -58,77 +71,123 @@ class DataXceiverServer implements Runnable {
   int maxXceiverCount =
     DFSConfigKeys.DFS_DATANODE_MAX_RECEIVER_THREADS_DEFAULT;
 
-  /** A manager to make sure that cluster balancing does not
-   * take too much resources.
-   * 
-   * It limits the number of block moves for balancing and
-   * the total amount of bandwidth they can use.
+  /**
+   * A manager to make sure that cluster balancing does not take too much
+   * resources.
+   *
+   * It limits the number of block moves for balancing and the total amount of
+   * bandwidth they can use.
    */
   static class BlockBalanceThrottler extends DataTransferThrottler {
-   private int numThreads;
-   private final AtomicInteger maxThreads = new AtomicInteger(0);
+    private final Semaphore semaphore;
+    private int maxThreads;
 
-   /**Constructor
-    * 
-    * @param bandwidth Total amount of bandwidth can be used for balancing 
+   /**
+    * Constructor.
+    *
+    * @param bandwidth Total amount of bandwidth can be used for balancing
     */
     private BlockBalanceThrottler(long bandwidth, int maxThreads) {
       super(bandwidth);
-      this.maxThreads.set(maxThreads);
+      this.semaphore = new Semaphore(maxThreads, true);
+      this.maxThreads = maxThreads;
       LOG.info("Balancing bandwidth is " + bandwidth + " bytes/s");
       LOG.info("Number threads for balancing is " + maxThreads);
     }
 
-    private void setMaxConcurrentMovers(int movers) {
-      this.maxThreads.set(movers);
+    /**
+     * Update the number of threads which may be used concurrently for moving
+     * blocks. The number of threads available can be scaled up or down. If
+     * increasing the number of threads, the request will be serviced
+     * immediately. However, if decreasing the number of threads, this method
+     * will block any new request for moves, wait for any existing backlog of
+     * move requests to clear, and wait for enough threads to have finished such
+     * that the total number of threads actively running is less than or equal
+     * to the new cap. If this method has been unable to successfully set the
+     * new, lower, cap within 'duration' seconds, the attempt will be aborted
+     * and the original cap will remain.
+     *
+     * @param newMaxThreads The new maximum number of threads for block moving
+     * @param duration The number of seconds to wait if decreasing threads
+     * @return true if new maximum was successfully applied; false otherwise
+     */
+    private boolean setMaxConcurrentMovers(final int newMaxThreads,
+        final int duration) {
+      Preconditions.checkArgument(newMaxThreads > 0);
+      final int delta = newMaxThreads - this.maxThreads;
+      LOG.debug("Change concurrent thread count to {} from {}", newMaxThreads,
+          this.maxThreads);
+      if (delta == 0) {
+        return true;
+      }
+      if (delta > 0) {
+        LOG.debug("Adding thread capacity: {}", delta);
+        this.semaphore.release(delta);
+        this.maxThreads = newMaxThreads;
+        return true;
+      }
+      try {
+        LOG.debug("Removing thread capacity: {}. Max wait: {}", delta,
+            duration);
+        boolean acquired = this.semaphore.tryAcquire(Math.abs(delta), duration,
+            TimeUnit.SECONDS);
+        if (acquired) {
+          this.maxThreads = newMaxThreads;
+        } else {
+          LOG.warn("Could not lower thread count to {} from {}. Too busy.",
+              newMaxThreads, this.maxThreads);
+        }
+        return acquired;
+      } catch (InterruptedException e) {
+        LOG.warn("Interrupted before adjusting thread count: {}", delta);
+        return false;
+      }
     }
 
     @VisibleForTesting
     int getMaxConcurrentMovers() {
-      return this.maxThreads.get();
+      return this.maxThreads;
     }
 
-   /** Check if the block move can start. 
-    * 
-    * Return true if the thread quota is not exceeded and 
+   /**
+    * Check if the block move can start
+    *
+    * Return true if the thread quota is not exceeded and
     * the counter is incremented; False otherwise.
     */
-    synchronized boolean acquire() {
-      if (numThreads >= maxThreads.get()) {
-        return false;
-      }
-      numThreads++;
-      return true;
+    boolean acquire() {
+      return this.semaphore.tryAcquire();
     }
 
-    /** Mark that the move is completed. The thread counter is decremented. */
-    synchronized void release() {
-      numThreads--;
+    /**
+     * Mark that the move is completed. The thread counter is decremented.
+     */
+    void release() {
+      this.semaphore.release();
     }
   }
 
   final BlockBalanceThrottler balanceThrottler;
-  
+
   /**
-   * We need an estimate for block size to check if the disk partition has
-   * enough space. Newer clients pass the expected block size to the DataNode.
-   * For older clients we just use the server-side default block size.
+   * Stores an estimate for block size to check if the disk partition has enough
+   * space. Newer clients pass the expected block size to the DataNode. For
+   * older clients, just use the server-side default block size.
    */
   final long estimateBlockSize;
-  
-  
+
   DataXceiverServer(PeerServer peerServer, Configuration conf,
       DataNode datanode) {
     this.peerServer = peerServer;
     this.datanode = datanode;
-    
-    this.maxXceiverCount = 
+
+    this.maxXceiverCount =
       conf.getInt(DFSConfigKeys.DFS_DATANODE_MAX_RECEIVER_THREADS_KEY,
                   DFSConfigKeys.DFS_DATANODE_MAX_RECEIVER_THREADS_DEFAULT);
-    
+
     this.estimateBlockSize = conf.getLongBytes(DFSConfigKeys.DFS_BLOCK_SIZE_KEY,
         DFSConfigKeys.DFS_BLOCK_SIZE_DEFAULT);
-    
+
     //set up parameter for cluster balancing
     this.balanceThrottler = new BlockBalanceThrottler(
         conf.getLongBytes(DFSConfigKeys.DFS_DATANODE_BALANCE_BANDWIDTHPERSEC_KEY,
@@ -161,25 +220,25 @@ class DataXceiverServer implements Runnable {
         // another thread closed our listener socket - that's expected during shutdown,
         // but not in other circumstances
         if (datanode.shouldRun && !datanode.shutdownForUpgrade) {
-          LOG.warn(datanode.getDisplayName() + ":DataXceiverServer: ", ace);
+          LOG.warn("{}:DataXceiverServer", datanode.getDisplayName(), ace);
         }
       } catch (IOException ie) {
-        IOUtils.cleanup(null, peer);
-        LOG.warn(datanode.getDisplayName() + ":DataXceiverServer: ", ie);
+        IOUtils.closeQuietly(peer);
+        LOG.warn("{}:DataXceiverServer", datanode.getDisplayName(), ie);
       } catch (OutOfMemoryError ie) {
-        IOUtils.cleanup(null, peer);
+        IOUtils.closeQuietly(peer);
         // DataNode can run out of memory if there is too many transfers.
         // Log the event, Sleep for 30 seconds, other transfers may complete by
         // then.
         LOG.error("DataNode is out of memory. Will retry in 30 seconds.", ie);
         try {
-          Thread.sleep(30 * 1000);
+          Thread.sleep(TimeUnit.SECONDS.toMillis(30L));
         } catch (InterruptedException e) {
           // ignore
         }
       } catch (Throwable te) {
-        LOG.error(datanode.getDisplayName()
-            + ":DataXceiverServer: Exiting due to: ", te);
+        LOG.error("{}:DataXceiverServer: Exiting.", datanode.getDisplayName(),
+            te);
         datanode.shouldRun = false;
       }
     }
@@ -189,8 +248,8 @@ class DataXceiverServer implements Runnable {
       peerServer.close();
       closed = true;
     } catch (IOException ie) {
-      LOG.warn(datanode.getDisplayName()
-          + " :DataXceiverServer: close exception", ie);
+      LOG.warn("{}:DataXceiverServer: close exception",
+          datanode.getDisplayName(), ie);
     }
 
     // if in restart prep stage, notify peers before closing them.
@@ -200,16 +259,10 @@ class DataXceiverServer implements Runnable {
       // to send an OOB message to the client, but blocked on network for
       // long time, we need to force its termination.
       LOG.info("Shutting down DataXceiverServer before restart");
-      // Allow roughly up to 2 seconds.
-      for (int i = 0; getNumPeers() > 0 && i < 10; i++) {
-        try {
-          Thread.sleep(200);
-        } catch (InterruptedException e) {
-          // ignore
-        }
-      }
+
+      waitAllPeers(2L, TimeUnit.SECONDS);
     }
-    // Close all peers.
+
     closeAllPeers();
   }
 
@@ -221,81 +274,158 @@ class DataXceiverServer implements Runnable {
       this.peerServer.close();
       this.closed = true;
     } catch (IOException ie) {
-      LOG.warn(datanode.getDisplayName() + ":DataXceiverServer.kill(): ", ie);
+      LOG.warn("{}:DataXceiverServer.kill()", datanode.getDisplayName(), ie);
     }
   }
-  
-  synchronized void addPeer(Peer peer, Thread t, DataXceiver xceiver)
+
+  void addPeer(Peer peer, Thread t, DataXceiver xceiver)
       throws IOException {
-    if (closed) {
-      throw new IOException("Server closed.");
+    lock.lock();
+    try {
+      if (closed) {
+        throw new IOException("Server closed.");
+      }
+      peers.put(peer, t);
+      peersXceiver.put(peer, xceiver);
+      datanode.metrics.incrDataNodeActiveXceiversCount();
+    } finally {
+      lock.unlock();
     }
-    peers.put(peer, t);
-    peersXceiver.put(peer, xceiver);
-    datanode.metrics.incrDataNodeActiveXceiversCount();
   }
 
-  synchronized void closePeer(Peer peer) {
-    peers.remove(peer);
-    peersXceiver.remove(peer);
-    datanode.metrics.decrDataNodeActiveXceiversCount();
-    IOUtils.cleanup(null, peer);
+  void closePeer(Peer peer) {
+    lock.lock();
+    try {
+      peers.remove(peer);
+      peersXceiver.remove(peer);
+      datanode.metrics.decrDataNodeActiveXceiversCount();
+      IOUtils.closeQuietly(peer);
+      if (peers.isEmpty()) {
+        this.noPeers.signalAll();
+      }
+    } finally {
+      lock.unlock();
+    }
   }
 
   // Sending OOB to all peers
-  public synchronized void sendOOBToPeers() {
-    if (!datanode.shutdownForUpgrade) {
-      return;
-    }
-
-    for (Peer p : peers.keySet()) {
-      try {
-        peersXceiver.get(p).sendOOB();
-      } catch (IOException e) {
-        LOG.warn("Got error when sending OOB message.", e);
-      } catch (InterruptedException e) {
-        LOG.warn("Interrupted when sending OOB message.");
+  public void sendOOBToPeers() {
+    lock.lock();
+    try {
+      if (!datanode.shutdownForUpgrade) {
+        return;
       }
+      for (Peer p : peers.keySet()) {
+        try {
+          peersXceiver.get(p).sendOOB();
+        } catch (IOException e) {
+          LOG.warn("Got error when sending OOB message.", e);
+        } catch (InterruptedException e) {
+          LOG.warn("Interrupted when sending OOB message.");
+        }
+      }
+    } finally {
+      lock.unlock();
     }
   }
 
-  public synchronized void stopWriters() {
-    for (Peer p : peers.keySet()) {
-      peersXceiver.get(p).stopWriter();
+  public void stopWriters() {
+    lock.lock();
+    try {
+      peers.keySet().forEach(p -> peersXceiver.get(p).stopWriter());
+    } finally {
+      lock.unlock();
     }
   }
-  
-  // Notify all peers of the shutdown and restart.
-  // datanode.shouldRun should still be true and datanode.restarting should
-  // be set true before calling this method.
-  synchronized void restartNotifyPeers() {
-    assert (datanode.shouldRun == true && datanode.shutdownForUpgrade);
-    for (Thread t : peers.values()) {
+
+  /**
+   * Notify all peers of the shutdown and restart. 'datanode.shouldRun' should
+   * still be true and 'datanode.restarting' should be set true before calling
+   * this method.
+   */
+  void restartNotifyPeers() {
+    assert (datanode.shouldRun && datanode.shutdownForUpgrade);
+    lock.lock();
+    try {
       // interrupt each and every DataXceiver thread.
-      t.interrupt();
+      peers.values().forEach(t -> t.interrupt());
+    } finally {
+      lock.unlock();
     }
   }
 
-  // Close all peers and clear the map.
-  synchronized void closeAllPeers() {
+  /**
+   * Close all peers and clear the map.
+   */
+  void closeAllPeers() {
     LOG.info("Closing all peers.");
-    for (Peer p : peers.keySet()) {
-      IOUtils.cleanup(null, p);
+    lock.lock();
+    try {
+      peers.keySet().forEach(p -> IOUtils.closeQuietly(p));
+      peers.clear();
+      peersXceiver.clear();
+      datanode.metrics.setDataNodeActiveXceiversCount(0);
+      this.noPeers.signalAll();
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  /**
+   * Causes a thread to block until all peers are removed, a certain amount of
+   * time has passed, or the thread is interrupted.
+   *
+   * @param timeout the maximum time to wait, in nanoseconds
+   * @param unit the unit of time to wait
+   * @return true if thread returned because all peers were removed; false
+   *         otherwise
+   */
+  private boolean waitAllPeers(long timeout, TimeUnit unit) {
+    long nanos = unit.toNanos(timeout);
+    lock.lock();
+    try {
+      while (!peers.isEmpty()) {
+        if (nanos <= 0L) {
+          return false;
+        }
+        nanos = noPeers.awaitNanos(nanos);
+      }
+    } catch (InterruptedException e) {
+      LOG.debug("Interrupted waiting for peers to close");
+      return false;
+    } finally {
+      lock.unlock();
     }
-    peers.clear();
-    peersXceiver.clear();
-    datanode.metrics.setDataNodeActiveXceiversCount(0);
+    return true;
   }
 
-  // Return the number of peers.
-  synchronized int getNumPeers() {
-    return peers.size();
+  /**
+   * Return the number of peers.
+   *
+   * @return the number of active peers
+   */
+  int getNumPeers() {
+    lock.lock();
+    try {
+      return peers.size();
+    } finally {
+      lock.unlock();
+    }
   }
 
-  // Return the number of peers and DataXceivers.
+  /**
+   * Return the number of peers and DataXceivers.
+   *
+   * @return the number of peers and DataXceivers.
+   */
   @VisibleForTesting
-  synchronized int getNumPeersXceiver() {
-    return peersXceiver.size();
+  int getNumPeersXceiver() {
+    lock.lock();
+    try {
+      return peersXceiver.size();
+    } finally {
+      lock.unlock();
+    }
   }
 
   @VisibleForTesting
@@ -303,13 +433,42 @@ class DataXceiverServer implements Runnable {
     return peerServer;
   }
 
-  synchronized void releasePeer(Peer peer) {
-    peers.remove(peer);
-    peersXceiver.remove(peer);
-    datanode.metrics.decrDataNodeActiveXceiversCount();
+  /**
+   * Release a peer.
+   *
+   * @param peer The peer to release
+   */
+  void releasePeer(Peer peer) {
+    lock.lock();
+    try {
+      peers.remove(peer);
+      peersXceiver.remove(peer);
+      datanode.metrics.decrDataNodeActiveXceiversCount();
+    } finally {
+      lock.unlock();
+    }
   }
 
-  public void updateBalancerMaxConcurrentMovers(int movers) {
-    balanceThrottler.setMaxConcurrentMovers(movers);
+  /**
+   * Update the number of threads which may be used concurrently for moving
+   * blocks.
+   *
+   * @param movers The new maximum number of threads for block moving
+   * @return true if new maximum was successfully applied; false otherwise
+   */
+  public boolean updateBalancerMaxConcurrentMovers(final int movers) {
+    return balanceThrottler.setMaxConcurrentMovers(movers,
+        this.maxReconfigureWaitTime);
+  }
+
+  /**
+   * Update the maximum amount of time to wait for reconfiguration of the
+   * maximum number of block mover threads to complete.
+   *
+   * @param max The new maximum number of threads for block moving, in seconds
+   */
+  @VisibleForTesting
+  void setMaxReconfigureWaitTime(int max) {
+    this.maxReconfigureWaitTime = max;
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeReconfiguration.java

@@ -176,55 +176,96 @@ public class TestDataNodeReconfiguration {
   @Test
   public void testAcquireWithMaxConcurrentMoversGreaterThanDefault()
       throws IOException, ReconfigurationException {
-    testAcquireWithMaxConcurrentMoversShared(10);
+    final DataNode[] dns = createDNsForTest(1);
+    try {
+      testAcquireOnMaxConcurrentMoversReconfiguration(dns[0], 10);
+    } finally {
+      dns[0].shutdown();
+    }
   }
 
   @Test
   public void testAcquireWithMaxConcurrentMoversLessThanDefault()
       throws IOException, ReconfigurationException {
-    testAcquireWithMaxConcurrentMoversShared(3);
+    final DataNode[] dns = createDNsForTest(1);
+    try {
+      testAcquireOnMaxConcurrentMoversReconfiguration(dns[0], 3);
+    } finally {
+      dns[0].shutdown();
+    }
   }
 
-  private void testAcquireWithMaxConcurrentMoversShared(
-      int maxConcurrentMovers)
+  /**
+   * Simulates a scenario where the DataNode has been reconfigured with fewer
+   * mover threads, but all of the current treads are busy and therefore the
+   * DataNode is unable to honor this request within a reasonable amount of
+   * time. The DataNode eventually gives up and returns a flag indicating that
+   * the request was not honored.
+   */
+  @Test
+  public void testFailedDecreaseConcurrentMovers()
       throws IOException, ReconfigurationException {
-    DataNode[] dns = null;
+    final DataNode[] dns = createDNsForTest(1);
+    final DataNode dataNode = dns[0];
     try {
-      dns = createDNsForTest(1);
-      testAcquireOnMaxConcurrentMoversReconfiguration(dns[0],
-          maxConcurrentMovers);
-    } catch (IOException ioe) {
-      throw ioe;
-    } catch (ReconfigurationException re) {
-      throw re;
+      // Set the current max to 2
+      dataNode.xserver.updateBalancerMaxConcurrentMovers(2);
+
+      // Simulate grabbing 2 threads
+      dataNode.xserver.balanceThrottler.acquire();
+      dataNode.xserver.balanceThrottler.acquire();
+
+      dataNode.xserver.setMaxReconfigureWaitTime(1);
+
+      // Attempt to set new maximum to 1
+      final boolean success =
+          dataNode.xserver.updateBalancerMaxConcurrentMovers(1);
+      Assert.assertFalse(success);
     } finally {
-      shutDownDNs(dns);
+      dataNode.shutdown();
     }
   }
 
-  private void shutDownDNs(DataNode[] dns) {
-    if (dns == null) {
-      return;
-    }
-
-    for (int i = 0; i < dns.length; i++) {
-      try {
-        if (dns[i] == null) {
-          continue;
-        }
-        dns[i].shutdown();
-      } catch (Exception e) {
-        LOG.error("Cannot close: ", e);
-      }
+  /**
+   * Test with invalid configuration.
+   */
+  @Test(expected = ReconfigurationException.class)
+  public void testFailedDecreaseConcurrentMoversReconfiguration()
+      throws IOException, ReconfigurationException {
+    final DataNode[] dns = createDNsForTest(1);
+    final DataNode dataNode = dns[0];
+    try {
+      // Set the current max to 2
+      dataNode.xserver.updateBalancerMaxConcurrentMovers(2);
+
+      // Simulate grabbing 2 threads
+      dataNode.xserver.balanceThrottler.acquire();
+      dataNode.xserver.balanceThrottler.acquire();
+
+      dataNode.xserver.setMaxReconfigureWaitTime(1);
+
+      // Now try reconfigure maximum downwards with threads released
+      dataNode.reconfigurePropertyImpl(
+          DFS_DATANODE_BALANCE_MAX_NUM_CONCURRENT_MOVES_KEY, "1");
+    } catch (ReconfigurationException e) {
+      Assert.assertEquals(DFS_DATANODE_BALANCE_MAX_NUM_CONCURRENT_MOVES_KEY,
+          e.getProperty());
+      Assert.assertEquals("1", e.getNewValue());
+      throw e;
+    } finally {
+      dataNode.shutdown();
     }
   }
 
   private void testAcquireOnMaxConcurrentMoversReconfiguration(
       DataNode dataNode, int maxConcurrentMovers) throws IOException,
       ReconfigurationException {
-    int defaultMaxThreads = dataNode.getConf().getInt(
+    final int defaultMaxThreads = dataNode.getConf().getInt(
         DFSConfigKeys.DFS_DATANODE_BALANCE_MAX_NUM_CONCURRENT_MOVES_KEY,
         DFSConfigKeys.DFS_DATANODE_BALANCE_MAX_NUM_CONCURRENT_MOVES_DEFAULT);
+
+    /** Test that the default setup is working */
+
     for (int i = 0; i < defaultMaxThreads; i++) {
       assertEquals("should be able to get thread quota", true,
           dataNode.xserver.balanceThrottler.acquire());
@@ -233,25 +274,24 @@ public class TestDataNodeReconfiguration {
     assertEquals("should not be able to get thread quota", false,
         dataNode.xserver.balanceThrottler.acquire());
 
+    // Give back the threads
+    for (int i = 0; i < defaultMaxThreads; i++) {
+      dataNode.xserver.balanceThrottler.release();
+    }
+
+    /** Test that the change is applied correctly */
+
     // change properties
     dataNode.reconfigureProperty(
         DFS_DATANODE_BALANCE_MAX_NUM_CONCURRENT_MOVES_KEY,
         String.valueOf(maxConcurrentMovers));
 
     assertEquals("thread quota is wrong", maxConcurrentMovers,
-        dataNode.xserver.balanceThrottler.getMaxConcurrentMovers()); // thread quota
+        dataNode.xserver.balanceThrottler.getMaxConcurrentMovers());
 
-    int val = Math.abs(maxConcurrentMovers - defaultMaxThreads);
-    if (defaultMaxThreads < maxConcurrentMovers) {
-      for (int i = 0; i < val; i++) {
-        assertEquals("should be able to get thread quota", true,
-            dataNode.xserver.balanceThrottler.acquire());
-      }
-    } else if (defaultMaxThreads > maxConcurrentMovers) {
-      for (int i = 0; i < val; i++) {
-        assertEquals("should not be able to get thread quota", false,
-            dataNode.xserver.balanceThrottler.acquire());
-      }
+    for (int i = 0; i < maxConcurrentMovers; i++) {
+      assertEquals("should be able to get thread quota", true,
+          dataNode.xserver.balanceThrottler.acquire());
     }
 
     assertEquals("should not be able to get thread quota", false,