svn merge -c 1215358 from trunk for HADOOP-7931.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23-PB@1230898 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -50,6 +50,9 @@ Release 0.23-PB - Unreleased
 
     HADOOP-7892. IPC logs too verbose after "RpcKind" introduction (todd)
 
+    HADOOP-7931. o.a.h.ipc.WritableRpcEngine should have a way to force
+                 initialization (atm)
+
 Release 0.23.1 - Unreleased
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/WritableRpcEngine.java

@@ -48,17 +48,38 @@ import org.apache.hadoop.conf.*;
 public class WritableRpcEngine implements RpcEngine {
   private static final Log LOG = LogFactory.getLog(RPC.class);
   
-  static { // Register the rpcRequest deserializer for WritableRpcEngine 
-    org.apache.hadoop.ipc.Server.registerProtocolEngine(RpcKind.RPC_WRITABLE,
-        Invocation.class, new Server.WritableRpcInvoker());
-  }
-
-  
   //writableRpcVersion should be updated if there is a change
   //in format of the rpc messages.
   
   // 2L - added declared class to Invocation
-  public static final long writableRpcVersion = 2L; 
+  public static final long writableRpcVersion = 2L;
+  
+  /**
+   * Whether or not this class has been initialized.
+   */
+  private static boolean isInitialized = false;
+  
+  static { 
+    ensureInitialized();
+  }
+  
+  /**
+   * Initialize this class if it isn't already.
+   */
+  public static synchronized void ensureInitialized() {
+    if (!isInitialized) {
+      initialize();
+    }
+  }
+  
+  /**
+   * Register the rpcRequest deserializer for WritableRpcEngine
+   */
+  private static synchronized void initialize() {
+    org.apache.hadoop.ipc.Server.registerProtocolEngine(RpcKind.RPC_WRITABLE,
+        Invocation.class, new Server.WritableRpcInvoker());
+    isInitialized = true;
+  }
 
   
   /** A method invocation, including the method name and its parameters.*/