How to use

getDatanodeByHost

method

in

org.apache.hadoop.hdfs.server.blockmanagement.Host2NodesMap

/** @return the datanode descriptor for the host. */
public DatanodeDescriptor getDatanodeByHost(final String host) {
 return host2DatanodeMap.getDatanodeByHost(host);
}

/** get a data node by its hostname. This should be used if only one 
 * datanode service is running on a hostname. If multiple datanodes
 * are running on a hostname then use methods getDataNodeByXferAddr and
 * getDataNodeByHostNameAndPort.
 * @return DatanodeDescriptor if found; otherwise null.
 */
DatanodeDescriptor getDataNodeByHostName(String hostname) {
 if(hostname == null) {
  return null;
 }
 
 hostmapLock.readLock().lock();
 try {
  String ipAddr = mapHost.get(hostname);
  if(ipAddr == null) {
   return null;
  } else {  
   return getDatanodeByHost(ipAddr);
  }
 } finally {
  hostmapLock.readLock().unlock();
 }
}

/** @return the datanode descriptor for the host. */
public DatanodeDescriptor getDatanodeByHost(final String host) {
 return host2DatanodeMap.getDatanodeByHost(host);
}

/** @return the datanode descriptor for the host. */
public DatanodeDescriptor getDatanodeByHost(final String host) {
 return host2DatanodeMap.getDatanodeByHost(host);
}

/** get a data node by its hostname. This should be used if only one 
 * datanode service is running on a hostname. If multiple datanodes
 * are running on a hostname then use methods getDataNodeByXferAddr and
 * getDataNodeByHostNameAndPort.
 * @return DatanodeDescriptor if found; otherwise null.
 */
DatanodeDescriptor getDataNodeByHostName(String hostname) {
 if(hostname == null) {
  return null;
 }
 
 hostmapLock.readLock().lock();
 try {
  String ipAddr = mapHost.get(hostname);
  if(ipAddr == null) {
   return null;
  } else {  
   return getDatanodeByHost(ipAddr);
  }
 } finally {
  hostmapLock.readLock().unlock();
 }
}

/** get a data node by its hostname. This should be used if only one 
 * datanode service is running on a hostname. If multiple datanodes
 * are running on a hostname then use methods getDataNodeByXferAddr and
 * getDataNodeByHostNameAndPort.
 * @return DatanodeDescriptor if found; otherwise null.
 */
DatanodeDescriptor getDataNodeByHostName(String hostname) {
 if(hostname == null) {
  return null;
 }
 
 hostmapLock.readLock().lock();
 try {
  String ipAddr = mapHost.get(hostname);
  if(ipAddr == null) {
   return null;
  } else {  
   return getDatanodeByHost(ipAddr);
  }
 } finally {
  hostmapLock.readLock().unlock();
 }
}

@Test
public void testGetDatanodeByHost() throws Exception {
 assertEquals(map.getDatanodeByHost("1.1.1.1"), dataNodes[0]);
 assertEquals(map.getDatanodeByHost("2.2.2.2"), dataNodes[1]);
 DatanodeDescriptor node = map.getDatanodeByHost("3.3.3.3");
 assertTrue(node == dataNodes[2] || node == dataNodes[3]);
 assertNull(map.getDatanodeByHost("4.4.4.4"));
}

@Test
public void testRemove() throws Exception {
 DatanodeDescriptor nodeNotInMap =
  DFSTestUtil.getDatanodeDescriptor("3.3.3.3", "/d1/r4");
 assertFalse(map.remove(nodeNotInMap));
 
 assertTrue(map.remove(dataNodes[0]));
 assertTrue(map.getDatanodeByHost("1.1.1.1.")==null);
 assertTrue(map.getDatanodeByHost("2.2.2.2")==dataNodes[1]);
 DatanodeDescriptor node = map.getDatanodeByHost("3.3.3.3");
 assertTrue(node==dataNodes[2] || node==dataNodes[3]);
 assertNull(map.getDatanodeByHost("4.4.4.4"));
 
 assertTrue(map.remove(dataNodes[2]));
 assertNull(map.getDatanodeByHost("1.1.1.1"));
 assertEquals(map.getDatanodeByHost("2.2.2.2"), dataNodes[1]);
 assertEquals(map.getDatanodeByHost("3.3.3.3"), dataNodes[3]);
 
 assertTrue(map.remove(dataNodes[3]));
 assertNull(map.getDatanodeByHost("1.1.1.1"));
 assertEquals(map.getDatanodeByHost("2.2.2.2"), dataNodes[1]);
 assertNull(map.getDatanodeByHost("3.3.3.3"));
 
 assertFalse(map.remove(null));
 assertTrue(map.remove(dataNodes[1]));
 assertFalse(map.remove(dataNodes[1]));
}