Apply HADOOP-7777 to 0.23.1

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1207628 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -6,6 +6,9 @@ Release 0.23.1 - Unreleased
 
   NEW FEATURES                                                                    
 
+    HADOOP-7777 Implement a base class for DNSToSwitchMapping implementations 
+    that can offer extra topology information. (stevel)
+
   IMPROVEMENTS
 
     HADOOP-7801. HADOOP_PREFIX cannot be overriden. (Bruno Mahé via tomwhite)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/AbstractDNSToSwitchMapping.java

@@ -0,0 +1,107 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.net;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.Configurable;
+import org.apache.hadoop.conf.Configuration;
+
+/**
+ * This is a base class for DNS to Switch mappings. <p/> It is not mandatory to
+ * derive {@link DNSToSwitchMapping} implementations from it, but it is strongly
+ * recommended, as it makes it easy for the Hadoop developers to add new methods
+ * to this base class that are automatically picked up by all implementations.
+ * <p/>
+ *
+ * This class does not extend the <code>Configured</code>
+ * base class, and should not be changed to do so, as it causes problems
+ * for subclasses. The constructor of the <code>Configured</code> calls
+ * the  {@link #setConf(Configuration)} method, which will call into the
+ * subclasses before they have been fully constructed.
+ *
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Evolving
+public abstract class AbstractDNSToSwitchMapping
+    implements DNSToSwitchMapping, Configurable {
+
+  private Configuration conf;
+
+  /**
+   * Create an unconfigured instance
+   */
+  protected AbstractDNSToSwitchMapping() {
+  }
+
+  /**
+   * Create an instance, caching the configuration file.
+   * This constructor does not call {@link #setConf(Configuration)}; if
+   * a subclass extracts information in that method, it must call it explicitly.
+   * @param conf the configuration
+   */
+  protected AbstractDNSToSwitchMapping(Configuration conf) {
+    this.conf = conf;
+  }
+
+  @Override
+  public Configuration getConf() {
+    return conf;
+  }
+
+  @Override
+  public void setConf(Configuration conf) {
+    this.conf = conf;
+  }
+
+  /**
+   * Predicate that indicates that the switch mapping is known to be
+   * single-switch. The base class returns false: it assumes all mappings are
+   * multi-rack. Subclasses may override this with methods that are more aware
+   * of their topologies.
+   *
+   * <p/>
+   *
+   * This method is used when parts of Hadoop need know whether to apply
+   * single rack vs multi-rack policies, such as during block placement.
+   * Such algorithms behave differently if they are on multi-switch systems.
+   * </p>
+   *
+   * @return true if the mapping thinks that it is on a single switch
+   */
+  public boolean isSingleSwitch() {
+    return false;
+  }
+
+  /**
+   * Query for a {@link DNSToSwitchMapping} instance being on a single
+   * switch.
+   * <p/>
+   * This predicate simply assumes that all mappings not derived from
+   * this class are multi-switch.
+   * @param mapping the mapping to query
+   * @return true if the base class says it is single switch, or the mapping
+   * is not derived from this class.
+   */
+  public static boolean isMappingSingleSwitch(DNSToSwitchMapping mapping) {
+    return mapping instanceof AbstractDNSToSwitchMapping
+        && ((AbstractDNSToSwitchMapping) mapping).isSingleSwitch();
+  }
+
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/CachedDNSToSwitchMapping.java

@@ -34,9 +34,13 @@ import org.apache.hadoop.classification.InterfaceStability;
  */
 @InterfaceAudience.Public
 @InterfaceStability.Evolving
-public class CachedDNSToSwitchMapping implements DNSToSwitchMapping {
+public class CachedDNSToSwitchMapping extends AbstractDNSToSwitchMapping {
   private Map<String, String> cache = new ConcurrentHashMap<String, String>();
-  protected DNSToSwitchMapping rawMapping;
+
+  /**
+   * The uncached mapping
+   */
+  protected final DNSToSwitchMapping rawMapping;
 
   /**
    * cache a raw DNS mapping
@@ -118,4 +122,14 @@ public class CachedDNSToSwitchMapping implements DNSToSwitchMapping {
     return getCachedHosts(names);
 
   }
+
+  /**
+   * Delegate the switch topology query to the raw mapping, via
+   * {@link AbstractDNSToSwitchMapping#isMappingSingleSwitch(DNSToSwitchMapping)}
+   * @return true iff the raw mapper is considered single-switch.
+   */
+  @Override
+  public boolean isSingleSwitch() {
+    return isMappingSingleSwitch(rawMapping);
+  }
 }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/DNSToSwitchMapping.java

@@ -40,6 +40,12 @@ public interface DNSToSwitchMapping {
    * Note the hostname/ip-address is not part of the returned path.
    * The network topology of the cluster would determine the number of
    * components in the network path.
+   * <p/>
+   *
+   * If a name cannot be resolved to a rack, the implementation
+   * should return {@link NetworkTopology#DEFAULT_RACK}. This
+   * is what the bundled implementations do, though it is not a formal requirement
+   *
    * @param names the list of hosts to resolve (can be empty)
    * @return list of resolved network paths.
    * If <i>names</i> is empty, the returned list is also empty

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/ScriptBasedMapping.java

@@ -32,16 +32,21 @@ import org.apache.hadoop.fs.CommonConfigurationKeys;
 
 /**
  * This class implements the {@link DNSToSwitchMapping} interface using a 
- * script configured via the {@link CommonConfigurationKeys#NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY}
+ * script configured via the
+ * {@link CommonConfigurationKeys#NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY} option.
+ * <p/>
+ * It contains a static class <code>RawScriptBasedMapping</code> that performs
+ * the work: reading the configuration parameters, executing any defined
+ * script, handling errors and such like. The outer
+ * class extends {@link CachedDNSToSwitchMapping} to cache the delegated
+ * queries.
+ * <p/>
+ * This DNS mapper's {@link #isSingleSwitch()} predicate returns
+ * true if and only if a script is defined.
  */
 @InterfaceAudience.Public
 @InterfaceStability.Evolving
-public final class ScriptBasedMapping extends CachedDNSToSwitchMapping 
-implements Configurable
-{
-  public ScriptBasedMapping() {
-    super(new RawScriptBasedMapping());
-  }
+public final class ScriptBasedMapping extends CachedDNSToSwitchMapping {
 
   /**
    * Minimum number of arguments: {@value}
@@ -65,6 +70,18 @@ implements Configurable
   static final String SCRIPT_ARG_COUNT_KEY =
                      CommonConfigurationKeys.NET_TOPOLOGY_SCRIPT_NUMBER_ARGS_KEY ;
 
+  /**
+   * Create an instance with the default configuration.
+   * </p>
+   * Calling {@link #setConf(Configuration)} will trigger a
+   * re-evaluation of the configuration settings and so be used to
+   * set up the mapping script.
+   *
+   */
+  public ScriptBasedMapping() {
+    super(new RawScriptBasedMapping());
+  }
+
   /**
    * Create an instance from the given configuration
    * @param conf configuration
@@ -74,14 +91,31 @@ implements Configurable
     setConf(conf);
   }
 
-  @Override
-  public Configuration getConf() {
-    return ((RawScriptBasedMapping)rawMapping).getConf();
+  /**
+   * Get the cached mapping and convert it to its real type
+   * @return the inner raw script mapping.
+   */
+  private RawScriptBasedMapping getRawMapping() {
+    return (RawScriptBasedMapping)rawMapping;
   }
 
+  @Override
+  public Configuration getConf() {
+    return getRawMapping().getConf();
+  }
+
+  /**
+   * {@inheritDoc}
+   * <p/>
+   * This will get called in the superclass constructor, so a check is needed
+   * to ensure that the raw mapping is defined before trying to relaying a null
+   * configuration.
+   * @param conf
+   */
   @Override
   public void setConf(Configuration conf) {
-    ((RawScriptBasedMapping)rawMapping).setConf(conf);
+    super.setConf(conf);
+    getRawMapping().setConf(conf);
   }
 
   /**
@@ -89,29 +123,26 @@ implements Configurable
    * by the superclass {@link CachedDNSToSwitchMapping}
    */
   private static final class RawScriptBasedMapping
-      implements DNSToSwitchMapping {
+      extends AbstractDNSToSwitchMapping {
     private String scriptName;
-    private Configuration conf;
     private int maxArgs; //max hostnames per call of the script
-    private static Log LOG =
+    private static final Log LOG =
         LogFactory.getLog(ScriptBasedMapping.class);
 
     /**
-     * Set the configuration and
-     * @param conf extract the configuration parameters of interest
+     * Set the configuration and extract the configuration parameters of interest
+     * @param conf the new configuration
      */
+    @Override
     public void setConf (Configuration conf) {
-      this.scriptName = conf.get(SCRIPT_FILENAME_KEY);
-      this.maxArgs = conf.getInt(SCRIPT_ARG_COUNT_KEY, DEFAULT_ARG_COUNT);
-      this.conf = conf;
-    }
-
-    /**
-     * Get the configuration
-     * @return the configuration
-     */
-    public Configuration getConf () {
-      return conf;
+      super.setConf(conf);
+      if (conf != null) {
+        scriptName = conf.get(SCRIPT_FILENAME_KEY);
+        maxArgs = conf.getInt(SCRIPT_ARG_COUNT_KEY, DEFAULT_ARG_COUNT);
+      } else {
+        scriptName = null;
+        maxArgs = 0;
+      }
     }
 
     /**
@@ -122,42 +153,42 @@ implements Configurable
 
     @Override
     public List<String> resolve(List<String> names) {
-    List <String> m = new ArrayList<String>(names.size());
-    
-    if (names.isEmpty()) {
-      return m;
-    }
+      List<String> m = new ArrayList<String>(names.size());
 
-    if (scriptName == null) {
-      for (int i = 0; i < names.size(); i++) {
-        m.add(NetworkTopology.DEFAULT_RACK);
+      if (names.isEmpty()) {
+        return m;
       }
-      return m;
-    }
-    
-    String output = runResolveCommand(names);
-    if (output != null) {
-      StringTokenizer allSwitchInfo = new StringTokenizer(output);
-      while (allSwitchInfo.hasMoreTokens()) {
-        String switchInfo = allSwitchInfo.nextToken();
-        m.add(switchInfo);
+
+      if (scriptName == null) {
+        for (String name : names) {
+          m.add(NetworkTopology.DEFAULT_RACK);
+        }
+        return m;
       }
-      
-      if (m.size() != names.size()) {
-        // invalid number of entries returned by the script
-        LOG.error("Script " + scriptName + " returned "
-            + Integer.toString(m.size()) + " values when "
-            + Integer.toString(names.size()) + " were expected.");
+
+      String output = runResolveCommand(names);
+      if (output != null) {
+        StringTokenizer allSwitchInfo = new StringTokenizer(output);
+        while (allSwitchInfo.hasMoreTokens()) {
+          String switchInfo = allSwitchInfo.nextToken();
+          m.add(switchInfo);
+        }
+
+        if (m.size() != names.size()) {
+          // invalid number of entries returned by the script
+          LOG.error("Script " + scriptName + " returned "
+              + Integer.toString(m.size()) + " values when "
+              + Integer.toString(names.size()) + " were expected.");
+          return null;
+        }
+      } else {
+        // an error occurred. return null to signify this.
+        // (exn was already logged in runResolveCommand)
         return null;
       }
-    } else {
-      // an error occurred. return null to signify this.
-      // (exn was already logged in runResolveCommand)
-      return null;
+
+      return m;
     }
-    
-    return m;
-  }
 
     /**
      * Build and execute the resolution command. The command is
@@ -195,10 +226,10 @@ implements Configurable
           dir = new File(userDir);
         }
         ShellCommandExecutor s = new ShellCommandExecutor(
-            cmdList.toArray(new String[0]), dir);
+            cmdList.toArray(new String[cmdList.size()]), dir);
         try {
           s.execute();
-          allOutput.append(s.getOutput() + " ");
+          allOutput.append(s.getOutput()).append(" ");
         } catch (Exception e) {
           LOG.warn("Exception: ", e);
           return null;
@@ -207,5 +238,15 @@ implements Configurable
       }
       return allOutput.toString();
     }
+
+    /**
+     * Declare that the mapper is single-switched if a script was not named
+     * in the configuration.
+     * @return true iff there is no script
+     */
+    @Override
+    public boolean isSingleSwitch() {
+      return scriptName == null;
+    }
   }
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/StaticMapping.java

@@ -17,34 +17,80 @@
  */
 package org.apache.hadoop.net;
 
-import java.util.*;
-
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.conf.Configured;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 /**
  * Implements the {@link DNSToSwitchMapping} via static mappings. Used
- * in testcases that simulate racks.
+ * in testcases that simulate racks, and in the
+ * {@link org.apache.hadoop.hdfs.MiniDFSCluster}
  *
+ * A shared, static mapping is used; to reset it call {@link #resetMap()}.
+ *
+ * When an instance of the class has its {@link #setConf(Configuration)}
+ * method called, nodes listed in the configuration will be added to the map.
+ * These do not get removed when the instance is garbage collected.
  */
-public class StaticMapping extends Configured implements DNSToSwitchMapping {
-  public void setconf(Configuration conf) {
-    String[] mappings = conf.getStrings("hadoop.configured.node.mapping");
-    if (mappings != null) {
-      for (int i = 0; i < mappings.length; i++) {
-        String str = mappings[i];
-        String host = str.substring(0, str.indexOf('='));
-        String rack = str.substring(str.indexOf('=') + 1);
-        addNodeToRack(host, rack);
+public class StaticMapping extends AbstractDNSToSwitchMapping  {
+
+  /**
+   * key to define the node mapping as a comma-delimited list of host=rack
+   * mappings, e.g. <code>host1=r1,host2=r1,host3=r2</code>.
+   * </p>
+   * <b>Important: </b>spaces not trimmed and are considered significant.
+   */
+  public static final String KEY_HADOOP_CONFIGURED_NODE_MAPPING =
+      "hadoop.configured.node.mapping";
+
+  /**
+   * Configure the mapping by extracting any mappings defined in the
+   * {@link #KEY_HADOOP_CONFIGURED_NODE_MAPPING} field
+   * @param conf new configuration
+   */
+  @Override
+  public void setConf(Configuration conf) {
+    super.setConf(conf);
+    if (conf != null) {
+      String[] mappings = conf.getStrings(KEY_HADOOP_CONFIGURED_NODE_MAPPING);
+      if (mappings != null) {
+        for (String str : mappings) {
+          String host = str.substring(0, str.indexOf('='));
+          String rack = str.substring(str.indexOf('=') + 1);
+          addNodeToRack(host, rack);
+        }
       }
     }
   }
-  /* Only one instance per JVM */
-  private static Map<String, String> nameToRackMap = new HashMap<String, String>();
-  
-  static synchronized public void addNodeToRack(String name, String rackId) {
-    nameToRackMap.put(name, rackId);
+
+  /**
+   * retained lower case setter for compatibility reasons; relays to
+   * {@link #setConf(Configuration)}
+   * @param conf new configuration
+   */
+  public void setconf(Configuration conf) {
+    setConf(conf);
   }
+
+  /* Only one instance per JVM */
+  private static final Map<String, String> nameToRackMap = new HashMap<String, String>();
+
+  /**
+   * Add a node to the static map. The moment any entry is added to the map,
+   * the map goes multi-rack.
+   * @param name node name
+   * @param rackId rack ID
+   */
+  public static void addNodeToRack(String name, String rackId) {
+    synchronized (nameToRackMap) {
+      nameToRackMap.put(name, rackId);
+    }
+  }
+
+  @Override
   public List<String> resolve(List<String> names) {
     List<String> m = new ArrayList<String>();
     synchronized (nameToRackMap) {
@@ -59,4 +105,24 @@ public class StaticMapping extends Configured implements DNSToSwitchMapping {
       return m;
     }
   }
+
+  /**
+   * This mapping is only single switch if the map is empty
+   * @return the current switching status
+   */
+  @Override
+  public boolean isSingleSwitch() {
+    synchronized (nameToRackMap) {
+      return nameToRackMap.isEmpty();
+    }
+  }
+
+  /**
+   * Clear the map and revert to being a single switch
+   */
+  public static void resetMap() {
+    synchronized (nameToRackMap) {
+      nameToRackMap.clear();
+    }
+  }
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/TestScriptBasedMapping.java

@@ -23,30 +23,59 @@ import java.util.List;
 import org.apache.hadoop.conf.Configuration;
 
 import junit.framework.TestCase;
+import org.junit.Test;
 
 public class TestScriptBasedMapping extends TestCase {
 
-  private ScriptBasedMapping mapping;
-  private Configuration conf;
-  private List<String> names;
+
   
   public TestScriptBasedMapping() {
-    mapping = new ScriptBasedMapping();
 
-    conf = new Configuration();
-    conf.setInt(ScriptBasedMapping.SCRIPT_ARG_COUNT_KEY,
-        ScriptBasedMapping.MIN_ALLOWABLE_ARGS - 1);
-    conf.set(ScriptBasedMapping.SCRIPT_FILENAME_KEY, "any-filename");
-
-    mapping.setConf(conf);    
   }
 
+  @Test
   public void testNoArgsMeansNoResult() {
-    names = new ArrayList<String>();
+    Configuration conf = new Configuration();
+    conf.setInt(ScriptBasedMapping.SCRIPT_ARG_COUNT_KEY,
+                ScriptBasedMapping.MIN_ALLOWABLE_ARGS - 1);
+    conf.set(ScriptBasedMapping.SCRIPT_FILENAME_KEY, "any-filename");
+    conf.set(ScriptBasedMapping.SCRIPT_FILENAME_KEY, "any-filename");
+    ScriptBasedMapping mapping = createMapping(conf);
+    List<String> names = new ArrayList<String>();
     names.add("some.machine.name");
     names.add("other.machine.name");
     List<String> result = mapping.resolve(names);
-    assertNull(result);
+    assertNull("Expected an empty list", result);
   }
 
+  @Test
+  public void testNoFilenameMeansSingleSwitch() throws Throwable {
+    Configuration conf = new Configuration();
+    ScriptBasedMapping mapping = createMapping(conf);
+    assertTrue("Expected to be single switch", mapping.isSingleSwitch());
+    assertTrue("Expected to be single switch",
+               AbstractDNSToSwitchMapping.isMappingSingleSwitch(mapping));
+  }
+
+  @Test
+  public void testFilenameMeansMultiSwitch() throws Throwable {
+    Configuration conf = new Configuration();
+    conf.set(ScriptBasedMapping.SCRIPT_FILENAME_KEY, "any-filename");
+    ScriptBasedMapping mapping = createMapping(conf);
+    assertFalse("Expected to be multi switch", mapping.isSingleSwitch());
+    mapping.setConf(new Configuration());
+    assertTrue("Expected to be single switch", mapping.isSingleSwitch());
+  }
+
+  @Test
+  public void testNullConfig() throws Throwable {
+    ScriptBasedMapping mapping = createMapping(null);
+    assertTrue("Expected to be single switch", mapping.isSingleSwitch());
+
+  }
+  private ScriptBasedMapping createMapping(Configuration conf) {
+    ScriptBasedMapping mapping = new ScriptBasedMapping();
+    mapping.setConf(conf);
+    return mapping;
+  }
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/TestStaticMapping.java

@@ -0,0 +1,103 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.net;
+
+import org.apache.hadoop.conf.Configuration;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Test the static mapping class.
+ * Because the map is actually static, this map needs to be reset for every test
+ */
+public class TestStaticMapping extends Assert {
+
+  /**
+   * Reset the map then create a new instance of the {@link StaticMapping}
+   * class
+   * @return a new instance
+   */
+  private StaticMapping newInstance() {
+    StaticMapping.resetMap();
+    return new StaticMapping();
+  }
+
+  @Test
+  public void testStaticIsSingleSwitch() throws Throwable {
+    StaticMapping mapping = newInstance();
+    assertTrue("Empty maps are not single switch", mapping.isSingleSwitch());
+  }
+
+
+  @Test
+  public void testCachingRelaysQueries() throws Throwable {
+    StaticMapping staticMapping = newInstance();
+    CachedDNSToSwitchMapping mapping =
+        new CachedDNSToSwitchMapping(staticMapping);
+    assertTrue("Expected single switch", mapping.isSingleSwitch());
+    StaticMapping.addNodeToRack("n1", "r1");
+    assertFalse("Expected to be multi switch",
+                mapping.isSingleSwitch());
+  }
+
+  @Test
+  public void testAddResolveNodes() throws Throwable {
+    StaticMapping mapping = newInstance();
+    StaticMapping.addNodeToRack("n1", "r1");
+    List<String> l1 = new ArrayList<String>(2);
+    l1.add("n1");
+    l1.add("unknown");
+    List<String> mappings = mapping.resolve(l1);
+    assertEquals(2, mappings.size());
+    assertEquals("r1", mappings.get(0));
+    assertEquals(NetworkTopology.DEFAULT_RACK, mappings.get(1));
+    assertFalse("Mapping is still single switch", mapping.isSingleSwitch());
+  }
+
+  @Test
+  public void testReadNodesFromConfig() throws Throwable {
+    StaticMapping mapping = newInstance();
+    Configuration conf = new Configuration();
+    conf.set(StaticMapping.KEY_HADOOP_CONFIGURED_NODE_MAPPING, "n1=r1,n2=r2");
+    mapping.setConf(conf);
+    List<String> l1 = new ArrayList<String>(3);
+    l1.add("n1");
+    l1.add("unknown");
+    l1.add("n2");
+    List<String> mappings = mapping.resolve(l1);
+    assertEquals(3, mappings.size());
+    assertEquals("r1", mappings.get(0));
+    assertEquals(NetworkTopology.DEFAULT_RACK, mappings.get(1));
+    assertEquals("r2", mappings.get(2));
+    assertFalse("Expected to be multi switch",
+                AbstractDNSToSwitchMapping.isMappingSingleSwitch(mapping));
+  }
+
+  @Test
+  public void testNullConfiguration() throws Throwable {
+    StaticMapping mapping = newInstance();
+    mapping.setConf(null);
+    assertTrue("Null maps is not single switch", mapping.isSingleSwitch());
+    assertTrue("Expected to be single switch",
+               AbstractDNSToSwitchMapping.isMappingSingleSwitch(mapping));
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/TestSwitchMapping.java

@@ -0,0 +1,53 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.net;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.List;
+
+/**
+ * Test some other details of the switch mapping
+ */
+public class TestSwitchMapping extends Assert {
+
+  @Test
+  public void testStandaloneClassesAssumedMultiswitch() throws Throwable {
+    DNSToSwitchMapping mapping = new StandaloneSwitchMapping();
+    assertFalse("Expected to be multi switch",
+                AbstractDNSToSwitchMapping.isMappingSingleSwitch(mapping));
+  }
+
+
+  @Test
+  public void testCachingRelays() throws Throwable {
+    CachedDNSToSwitchMapping mapping =
+        new CachedDNSToSwitchMapping(new StandaloneSwitchMapping());
+    assertFalse("Expected to be multi switch",
+                mapping.isSingleSwitch());
+  }
+
+  private static class StandaloneSwitchMapping implements DNSToSwitchMapping {
+    @Override
+    public List<String> resolve(List<String> names) {
+      return names;
+    }
+  }
+}