YARN-8435. Fix NPE when the same client simultaneously contact for the first time Yarn Router. Contributed by Rang Jiaheng.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/clientrm/RouterClientRMService.java

@@ -430,13 +430,15 @@ public GetAllResourceTypeInfoResponse getResourceTypeInfo(
     return pipeline.getRootInterceptor().getResourceTypeInfo(request);
   }
 
-  private RequestInterceptorChainWrapper getInterceptorChain()
+  @VisibleForTesting
+  protected RequestInterceptorChainWrapper getInterceptorChain()
       throws IOException {
     String user = UserGroupInformation.getCurrentUser().getUserName();
-    if (!userPipelineMap.containsKey(user)) {
-      initializePipeline(user);
+    RequestInterceptorChainWrapper chain = userPipelineMap.get(user);
+    if (chain != null && chain.getRootInterceptor() != null) {
+      return chain;
     }
-    return userPipelineMap.get(user);
+    return initializePipeline(user);
   }
 
   /**
@@ -503,37 +505,34 @@ protected ClientRequestInterceptor createRequestInterceptorChain() {
    *
    * @param user
    */
-  private void initializePipeline(String user) {
-    RequestInterceptorChainWrapper chainWrapper = null;
+  private RequestInterceptorChainWrapper initializePipeline(String user) {
     synchronized (this.userPipelineMap) {
       if (this.userPipelineMap.containsKey(user)) {
         LOG.info("Request to start an already existing user: {}"
             + " was received, so ignoring.", user);
-        return;
+        return userPipelineMap.get(user);
       }
 
-      chainWrapper = new RequestInterceptorChainWrapper();
-      this.userPipelineMap.put(user, chainWrapper);
-    }
-
-    // We register the pipeline instance in the map first and then initialize it
-    // later because chain initialization can be expensive and we would like to
-    // release the lock as soon as possible to prevent other applications from
-    // blocking when one application's chain is initializing
+      RequestInterceptorChainWrapper chainWrapper =
+          new RequestInterceptorChainWrapper();
+      try {
+        // We should init the pipeline instance after it is created and then
+        // add to the map, to ensure thread safe.
         LOG.info("Initializing request processing pipeline for application "
             + "for the user: {}", user);
 
-    try {
         ClientRequestInterceptor interceptorChain =
             this.createRequestInterceptorChain();
         interceptorChain.init(user);
         chainWrapper.init(interceptorChain);
       } catch (Exception e) {
-      synchronized (this.userPipelineMap) {
-        this.userPipelineMap.remove(user);
-      }
+        LOG.error("Init ClientRequestInterceptor error for user: " + user, e);
         throw e;
       }
+
+      this.userPipelineMap.put(user, chainWrapper);
+      return chainWrapper;
+    }
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/rmadmin/RouterRMAdminService.java

@@ -165,13 +165,15 @@ private List<String> getInterceptorClassNames(Configuration conf) {
     return interceptorClassNames;
   }
 
-  private RequestInterceptorChainWrapper getInterceptorChain()
+  @VisibleForTesting
+  protected RequestInterceptorChainWrapper getInterceptorChain()
       throws IOException {
     String user = UserGroupInformation.getCurrentUser().getUserName();
-    if (!userPipelineMap.containsKey(user)) {
-      initializePipeline(user);
+    RequestInterceptorChainWrapper chain = userPipelineMap.get(user);
+    if (chain != null && chain.getRootInterceptor() != null) {
+      return chain;
     }
-    return userPipelineMap.get(user);
+    return initializePipeline(user);
   }
 
   /**
@@ -239,36 +241,33 @@ protected RMAdminRequestInterceptor createRequestInterceptorChain() {
    *
    * @param user
    */
-  private void initializePipeline(String user) {
-    RequestInterceptorChainWrapper chainWrapper = null;
+  private RequestInterceptorChainWrapper initializePipeline(String user) {
     synchronized (this.userPipelineMap) {
       if (this.userPipelineMap.containsKey(user)) {
         LOG.info("Request to start an already existing user: {}"
             + " was received, so ignoring.", user);
-        return;
+        return userPipelineMap.get(user);
       }
 
-      chainWrapper = new RequestInterceptorChainWrapper();
-      this.userPipelineMap.put(user, chainWrapper);
-    }
-
-    // We register the pipeline instance in the map first and then initialize it
-    // later because chain initialization can be expensive and we would like to
-    // release the lock as soon as possible to prevent other applications from
-    // blocking when one application's chain is initializing
-    LOG.info("Initializing request processing pipeline for the user: {}", user);
-
+      RequestInterceptorChainWrapper chainWrapper =
+          new RequestInterceptorChainWrapper();
       try {
+        // We should init the pipeline instance after it is created and then
+        // add to the map, to ensure thread safe.
+        LOG.info("Initializing request processing pipeline for user: {}", user);
+
         RMAdminRequestInterceptor interceptorChain =
             this.createRequestInterceptorChain();
         interceptorChain.init(user);
         chainWrapper.init(interceptorChain);
       } catch (Exception e) {
-      synchronized (this.userPipelineMap) {
-        this.userPipelineMap.remove(user);
-      }
+        LOG.error("Init RMAdminRequestInterceptor error for user: " + user, e);
         throw e;
       }
+
+      this.userPipelineMap.put(user, chainWrapper);
+      return chainWrapper;
+    }
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/webapp/RouterWebServices.java

@@ -173,10 +173,11 @@ protected RequestInterceptorChainWrapper getInterceptorChain(
     } catch (IOException e) {
       LOG.error("Cannot get user: {}", e.getMessage());
     }
-    if (!userPipelineMap.containsKey(user)) {
-      initializePipeline(user);
+    RequestInterceptorChainWrapper chain = userPipelineMap.get(user);
+    if (chain != null && chain.getRootInterceptor() != null) {
+      return chain;
     }
-    return userPipelineMap.get(user);
+    return initializePipeline(user);
   }
 
   /**
@@ -242,36 +243,33 @@ protected RESTRequestInterceptor createRequestInterceptorChain() {
    *
    * @param user
    */
-  private void initializePipeline(String user) {
-    RequestInterceptorChainWrapper chainWrapper = null;
+  private RequestInterceptorChainWrapper initializePipeline(String user) {
     synchronized (this.userPipelineMap) {
       if (this.userPipelineMap.containsKey(user)) {
         LOG.info("Request to start an already existing user: {}"
             + " was received, so ignoring.", user);
-        return;
+        return userPipelineMap.get(user);
       }
 
-      chainWrapper = new RequestInterceptorChainWrapper();
-      this.userPipelineMap.put(user, chainWrapper);
-    }
-
-    // We register the pipeline instance in the map first and then initialize it
-    // later because chain initialization can be expensive and we would like to
-    // release the lock as soon as possible to prevent other applications from
-    // blocking when one application's chain is initializing
-    LOG.info("Initializing request processing pipeline for the user: {}", user);
-
+      RequestInterceptorChainWrapper chainWrapper =
+          new RequestInterceptorChainWrapper();
       try {
+        // We should init the pipeline instance after it is created and then
+        // add to the map, to ensure thread safe.
+        LOG.info("Initializing request processing pipeline for user: {}", user);
+
         RESTRequestInterceptor interceptorChain =
             this.createRequestInterceptorChain();
         interceptorChain.init(user);
         chainWrapper.init(interceptorChain);
       } catch (Exception e) {
-      synchronized (this.userPipelineMap) {
-        this.userPipelineMap.remove(user);
-      }
+        LOG.error("Init RESTRequestInterceptor error for user: " + user, e);
         throw e;
       }
+
+      this.userPipelineMap.put(user, chainWrapper);
+      return chainWrapper;
+    }
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/clientrm/TestRouterClientRMService.java

@@ -19,8 +19,10 @@
 package org.apache.hadoop.yarn.server.router.clientrm;
 
 import java.io.IOException;
+import java.security.PrivilegedExceptionAction;
 import java.util.Map;
 
+import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.yarn.api.protocolrecords.GetClusterMetricsResponse;
 import org.apache.hadoop.yarn.api.protocolrecords.GetClusterNodeLabelsResponse;
 import org.apache.hadoop.yarn.api.protocolrecords.GetClusterNodesResponse;
@@ -207,4 +209,62 @@ public void testUsersChainMapWithLRUCache()
     Assert.assertNull("test2 should have been evicted", chain);
   }
 
+  /**
+   * This test validates if the ClientRequestInterceptor chain for the user
+   * can build and init correctly when a multi-client process begins to
+   * request RouterClientRMService for the same user simultaneously.
+   */
+  @Test
+  public void testClientPipelineConcurrent() throws InterruptedException {
+    final String user = "test1";
+
+    /*
+     * ClientTestThread is a thread to simulate a client request to get a
+     * ClientRequestInterceptor for the user.
+     */
+    class ClientTestThread extends Thread {
+      private ClientRequestInterceptor interceptor;
+      @Override public void run() {
+        try {
+          interceptor = pipeline();
+        } catch (IOException | InterruptedException e) {
+          e.printStackTrace();
+        }
+      }
+      private ClientRequestInterceptor pipeline()
+          throws IOException, InterruptedException {
+        return UserGroupInformation.createRemoteUser(user).doAs(
+            new PrivilegedExceptionAction<ClientRequestInterceptor>() {
+              @Override
+              public ClientRequestInterceptor run() throws Exception {
+                RequestInterceptorChainWrapper wrapper =
+                    getRouterClientRMService().getInterceptorChain();
+                ClientRequestInterceptor interceptor =
+                    wrapper.getRootInterceptor();
+                Assert.assertNotNull(interceptor);
+                LOG.info("init client interceptor success for user " + user);
+                return interceptor;
+              }
+            });
+      }
+    }
+
+    /*
+     * We start the first thread. It should not finish initing a chainWrapper
+     * before the other thread starts. In this way, the second thread can
+     * init at the same time of the first one. In the end, we validate that
+     * the 2 threads get the same chainWrapper without going into error.
+     */
+    ClientTestThread client1 = new ClientTestThread();
+    ClientTestThread client2 = new ClientTestThread();
+    client1.start();
+    client2.start();
+    client1.join();
+    client2.join();
+
+    Assert.assertNotNull(client1.interceptor);
+    Assert.assertNotNull(client2.interceptor);
+    Assert.assertTrue(client1.interceptor == client2.interceptor);
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/rmadmin/TestRouterRMAdminService.java

@@ -19,8 +19,10 @@
 package org.apache.hadoop.yarn.server.router.rmadmin;
 
 import java.io.IOException;
+import java.security.PrivilegedExceptionAction;
 import java.util.Map;
 
+import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.yarn.exceptions.YarnException;
 import org.apache.hadoop.yarn.server.api.protocolrecords.AddToClusterNodeLabelsResponse;
 import org.apache.hadoop.yarn.server.api.protocolrecords.CheckForDecommissioningNodesResponse;
@@ -216,4 +218,62 @@ public void testUsersChainMapWithLRUCache()
     Assert.assertNull("test2 should have been evicted", chain);
   }
 
+  /**
+   * This test validates if the RMAdminRequestInterceptor chain for the user
+   * can build and init correctly when a multi-client process begins to
+   * request RouterRMAdminService for the same user simultaneously.
+   */
+  @Test
+  public void testRMAdminPipelineConcurrent() throws InterruptedException {
+    final String user = "test1";
+
+    /*
+     * ClientTestThread is a thread to simulate a client request to get a
+     * RMAdminRequestInterceptor for the user.
+     */
+    class ClientTestThread extends Thread {
+      private RMAdminRequestInterceptor interceptor;
+      @Override public void run() {
+        try {
+          interceptor = pipeline();
+        } catch (IOException | InterruptedException e) {
+          e.printStackTrace();
+        }
+      }
+      private RMAdminRequestInterceptor pipeline()
+          throws IOException, InterruptedException {
+        return UserGroupInformation.createRemoteUser(user).doAs(
+            new PrivilegedExceptionAction<RMAdminRequestInterceptor>() {
+              @Override
+              public RMAdminRequestInterceptor run() throws Exception {
+                RequestInterceptorChainWrapper wrapper =
+                    getRouterRMAdminService().getInterceptorChain();
+                RMAdminRequestInterceptor interceptor =
+                    wrapper.getRootInterceptor();
+                Assert.assertNotNull(interceptor);
+                LOG.info("init rm admin interceptor success for user" + user);
+                return interceptor;
+              }
+            });
+      }
+    }
+
+    /*
+     * We start the first thread. It should not finish initing a chainWrapper
+     * before the other thread starts. In this way, the second thread can
+     * init at the same time of the first one. In the end, we validate that
+     * the 2 threads get the same chainWrapper without going into error.
+     */
+    ClientTestThread client1 = new ClientTestThread();
+    ClientTestThread client2 = new ClientTestThread();
+    client1.start();
+    client2.start();
+    client1.join();
+    client2.join();
+
+    Assert.assertNotNull(client1.interceptor);
+    Assert.assertNotNull(client2.interceptor);
+    Assert.assertTrue(client1.interceptor == client2.interceptor);
+  }
+
 }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/TestRouterWebServices.java

@@ -19,10 +19,12 @@
 package org.apache.hadoop.yarn.server.router.webapp;
 
 import java.io.IOException;
+import java.security.PrivilegedExceptionAction;
 import java.util.Map;
 
 import javax.ws.rs.core.Response;
 
+import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.yarn.exceptions.YarnException;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.ActivitiesInfo;
 import org.apache.hadoop.yarn.server.resourcemanager.webapp.dao.AppActivitiesInfo;
@@ -49,12 +51,17 @@
 import org.apache.hadoop.yarn.server.webapp.dao.ContainersInfo;
 import org.junit.Assert;
 import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Test class to validate the WebService interceptor model inside the Router.
  */
 public class TestRouterWebServices extends BaseRouterWebServicesTest {
 
+  private static final Logger LOG =
+      LoggerFactory.getLogger(TestRouterWebServices.class);
+
   private String user = "test1";
 
   /**
@@ -266,4 +273,62 @@ public void testUsersChainMapWithLRUCache()
     Assert.assertNull("test2 should have been evicted", chain);
   }
 
+  /**
+   * This test validates if the RESTRequestInterceptor chain for the user
+   * can build and init correctly when a multi-client process begins to
+   * request RouterWebServices for the same user simultaneously.
+   */
+  @Test
+  public void testWebPipelineConcurrent() throws InterruptedException {
+    final String user = "test1";
+
+    /*
+     * ClientTestThread is a thread to simulate a client request to get a
+     * RESTRequestInterceptor for the user.
+     */
+    class ClientTestThread extends Thread {
+      private RESTRequestInterceptor interceptor;
+      @Override public void run() {
+        try {
+          interceptor = pipeline();
+        } catch (IOException | InterruptedException e) {
+          e.printStackTrace();
+        }
+      }
+      private RESTRequestInterceptor pipeline()
+          throws IOException, InterruptedException {
+        return UserGroupInformation.createRemoteUser(user).doAs(
+            new PrivilegedExceptionAction<RESTRequestInterceptor>() {
+              @Override
+              public RESTRequestInterceptor run() throws Exception {
+                RequestInterceptorChainWrapper wrapper =
+                    getInterceptorChain(user);
+                RESTRequestInterceptor interceptor =
+                    wrapper.getRootInterceptor();
+                Assert.assertNotNull(interceptor);
+                LOG.info("init web interceptor success for user" + user);
+                return interceptor;
+              }
+            });
+      }
+    }
+
+    /*
+     * We start the first thread. It should not finish initing a chainWrapper
+     * before the other thread starts. In this way, the second thread can
+     * init at the same time of the first one. In the end, we validate that
+     * the 2 threads get the same chainWrapper without going into error.
+     */
+    ClientTestThread client1 = new ClientTestThread();
+    ClientTestThread client2 = new ClientTestThread();
+    client1.start();
+    client2.start();
+    client1.join();
+    client2.join();
+
+    Assert.assertNotNull(client1.interceptor);
+    Assert.assertNotNull(client2.interceptor);
+    Assert.assertTrue(client1.interceptor == client2.interceptor);
+  }
+
 }