YARN-3626. On Windows localized resources are not moved to the front of the classpath when they should be. Contributed by Craig Welch.

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/job/impl/TaskAttemptImpl.java

@@ -931,10 +931,16 @@ static ContainerLaunchContext createContainerLaunchContext(
     // Fill in the fields needed per-container that are missing in the common
     // spec.
 
+    boolean userClassesTakesPrecedence =
+      conf.getBoolean(MRJobConfig.MAPREDUCE_JOB_USER_CLASSPATH_FIRST, false);
+
     // Setup environment by cloning from common env.
     Map<String, String> env = commonContainerSpec.getEnvironment();
     Map<String, String> myEnv = new HashMap<String, String>(env.size());
     myEnv.putAll(env);
+    if (userClassesTakesPrecedence) {
+      myEnv.put(Environment.CLASSPATH_PREPEND_DISTCACHE.name(), "true");
+    }
     MapReduceChildJVM.setVMEnv(myEnv, remoteTask);
 
     // Set up the launch command

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-common/src/main/java/org/apache/hadoop/mapreduce/v2/util/MRApps.java

@@ -241,11 +241,6 @@ public static void setClasspath(Map<String, String> environment,
     boolean userClassesTakesPrecedence = 
       conf.getBoolean(MRJobConfig.MAPREDUCE_JOB_USER_CLASSPATH_FIRST, false);
 
-    if (userClassesTakesPrecedence) {
-      conf.set(YarnConfiguration.YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE,
-        "true");
-    }
-
     String classpathEnvVar =
       conf.getBoolean(MRJobConfig.MAPREDUCE_JOB_CLASSLOADER, false)
         ? Environment.APP_CLASSPATH.name() : Environment.CLASSPATH.name();

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/ApplicationConstants.java

@@ -19,6 +19,7 @@
 package org.apache.hadoop.yarn.api;
 
 import org.apache.hadoop.classification.InterfaceAudience.Public;
+import org.apache.hadoop.classification.InterfaceAudience.Private;
 import org.apache.hadoop.classification.InterfaceStability.Evolving;
 import org.apache.hadoop.classification.InterfaceStability.Unstable;
 import org.apache.hadoop.security.UserGroupInformation;
@@ -190,6 +191,13 @@ public enum Environment {
      */
     HADOOP_YARN_HOME("HADOOP_YARN_HOME"),
 
+    /**
+     * $CLASSPATH_PREPEND_DISTCACHE
+     * Private, Windows specific
+     */
+    @Private
+    CLASSPATH_PREPEND_DISTCACHE("CLASSPATH_PREPEND_DISTCACHE"),
+
     /**
      * $CONTAINER_ID
      * Final, exported by NodeManager and non-modifiable by users.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/conf/YarnConfiguration.java

@@ -611,6 +611,7 @@ private static void addDeprecatedKeys() {
       ApplicationConstants.Environment.HADOOP_COMMON_HOME.key(),
       ApplicationConstants.Environment.HADOOP_HDFS_HOME.key(),
       ApplicationConstants.Environment.HADOOP_CONF_DIR.key(),
+      ApplicationConstants.Environment.CLASSPATH_PREPEND_DISTCACHE.key(),
       ApplicationConstants.Environment.HADOOP_YARN_HOME.key()));
   
   /** address of node manager IPC.*/
@@ -1279,16 +1280,6 @@ private static void addDeprecatedKeys() {
   public static final String YARN_APPLICATION_CLASSPATH = YARN_PREFIX
       + "application.classpath";
 
-  /**
-   * Whether or not entries from the distributed cache should be preferred over
-   * the rest of the YARN CLASSPATH
-   */
-  public static final String YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE =
-    YARN_PREFIX + "application.classpath.prepend.distcache";
-
-  public static final boolean
-    DEFAULT_YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE = false;
-
   /**
    * Default platform-agnostic CLASSPATH for YARN applications. A
    * comma-separated list of CLASSPATH entries. The parameter expansion marker

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/launcher/ContainerLaunch.java

@@ -749,11 +749,12 @@ public void sanitizeEnv(Map<String, String> environment, Path pwd,
         //jar is created and so they "are lost" and have to be explicitly
         //added to the classpath instead.  This also means that their position
         //is lost relative to other non-distcache classpath entries which will
-        //break things like mapreduce.job.user.classpath.first.
+        //break things like mapreduce.job.user.classpath.first.  An environment
+        //variable can be set to indicate that distcache entries should come
+        //first
 
-        boolean preferLocalizedJars = conf.getBoolean(
-          YarnConfiguration.YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE,
-          YarnConfiguration.DEFAULT_YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE
+        boolean preferLocalizedJars = Boolean.valueOf(
+          environment.get(Environment.CLASSPATH_PREPEND_DISTCACHE.name())
           );
 
         boolean needsSeparator = false;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/test/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/launcher/TestContainerLaunch.java

@@ -417,7 +417,7 @@ public void testPrependDistcache() throws Exception {
     userSetEnv.put(Environment.LOGNAME.name(), "user_set_LOGNAME");
     userSetEnv.put(Environment.PWD.name(), "user_set_PWD");
     userSetEnv.put(Environment.HOME.name(), "user_set_HOME");
-    userSetEnv.put(Environment.CLASSPATH.name(), "SYSTEM_CLPATH");
+    userSetEnv.put(Environment.CLASSPATH.name(), "APATH");
     containerLaunchContext.setEnvironment(userSetEnv);
     Container container = mock(Container.class);
     when(container.getContainerId()).thenReturn(cId);
@@ -463,14 +463,12 @@ public void handle(Event event) {
     Assert.assertTrue(
       result.get(result.size() - 1).endsWith("userjarlink.jar"));
 
-    //Now move userjar to the front
+    //Then, with user classpath first
+    userSetEnv.put(Environment.CLASSPATH_PREPEND_DISTCACHE.name(), "true");
 
     cId = ContainerId.newContainerId(appAttemptId, 1);
     when(container.getContainerId()).thenReturn(cId);
 
-    conf.set(YarnConfiguration.YARN_APPLICATION_CLASSPATH_PREPEND_DISTCACHE,
-      "true");
-
     launch = new ContainerLaunch(distContext, conf,
         dispatcher, exec, null, container, dirsHandler, containerManager);