HADOOP-18625. Fix method name of RPC.Builder#setnumReaders (#5301)

Changes method name of RPC.Builder#setnumReaders to setNumReaders()

The original method is still there, just marked deprecated.
It is the one which should be used when working with older branches.

Contributed by Haiyang Hu

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

@@ -896,15 +896,29 @@ public class RPC {
       this.numHandlers = numHandlers;
       return this;
     }
-    
+
     /**
      * @return Default: -1.
      * @param numReaders input numReaders.
+     * @deprecated call {@link #setNumReaders(int value)} instead.
      */
+    @Deprecated
     public Builder setnumReaders(int numReaders) {
       this.numReaders = numReaders;
       return this;
     }
+
+    /**
+     * Set the number of reader threads.
+     *
+     * @return this builder.
+     * @param value input numReaders.
+     * @since HADOOP-18625.
+     */
+    public Builder setNumReaders(int value) {
+      this.numReaders = value;
+      return this;
+    }
     
     /**
      * @return Default: -1.

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestRPC.java

@@ -378,7 +378,7 @@ public class TestRPC extends TestRpcBase {
     assertEquals(confReaders, server.getNumReaders());
 
     server = newServerBuilder(conf)
-        .setNumHandlers(1).setnumReaders(3).setQueueSizePerHandler(200)
+        .setNumHandlers(1).setNumReaders(3).setQueueSizePerHandler(200)
         .setVerbose(false).build();
 
     assertEquals(3, server.getNumReaders());

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcServer.java

@@ -333,7 +333,7 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol,
         .setBindAddress(confRpcAddress.getHostName())
         .setPort(confRpcAddress.getPort())
         .setNumHandlers(handlerCount)
-        .setnumReaders(readerCount)
+        .setNumReaders(readerCount)
         .setQueueSizePerHandler(handlerQueueSize)
         .setVerbose(false)
         .setAlignmentContext(routerStateIdContext)