Merge pull request #1881 from duhenglucky/issue_1879

[ISSUE #1879] Prevent blocked by group transfer service

broker/src/main/java/org/apache/rocketmq/broker/BrokerController.java

@@ -1240,6 +1240,7 @@ public class BrokerController {
         }
     }
 
-
-
+    public ExecutorService getSendMessageExecutor() {
+        return sendMessageExecutor;
+    }
 }

broker/src/main/java/org/apache/rocketmq/broker/processor/SendMessageProcessor.java

@@ -79,7 +79,7 @@ public class SendMessageProcessor extends AbstractSendMessageProcessor implement
 
     @Override
     public void asyncProcessRequest(ChannelHandlerContext ctx, RemotingCommand request, RemotingResponseCallback responseCallback) throws Exception {
-        asyncProcessRequest(ctx, request).thenAccept(responseCallback::callback);
+        asyncProcessRequest(ctx, request).thenAcceptAsync(responseCallback::callback, this.brokerController.getSendMessageExecutor());
     }
 
     public CompletableFuture<RemotingCommand> asyncProcessRequest(ChannelHandlerContext ctx,