From e0881448c13ada1972f41685d2a6716681b7d192 Mon Sep 17 00:00:00 2001
From: Francesco Nigro <nigro.fra@gmail.com>
Date: Mon, 21 Aug 2017 15:03:17 +0200
Subject: [PATCH] ARTEMIS-1356 Avoid allocations and atomic operations to
 recognize handler's thread

---
 .../core/ServerSessionPacketHandler.java      | 30 +++++++++++++++----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/artemis-server/src/main/java/org/apache/activemq/artemis/core/protocol/core/ServerSessionPacketHandler.java b/artemis-server/src/main/java/org/apache/activemq/artemis/core/protocol/core/ServerSessionPacketHandler.java
index 7b45c9f8d6..58518a93e1 100644
--- a/artemis-server/src/main/java/org/apache/activemq/artemis/core/protocol/core/ServerSessionPacketHandler.java
+++ b/artemis-server/src/main/java/org/apache/activemq/artemis/core/protocol/core/ServerSessionPacketHandler.java
@@ -19,7 +19,6 @@ package org.apache.activemq.artemis.core.protocol.core;
 import javax.transaction.xa.XAResource;
 import javax.transaction.xa.Xid;
 import java.util.List;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.activemq.artemis.api.core.ActiveMQException;
 import org.apache.activemq.artemis.api.core.ActiveMQExceptionType;
@@ -159,7 +158,11 @@ public class ServerSessionPacketHandler implements ChannelHandler {
 
    private final boolean direct;
 
-   private static final ThreadLocal<AtomicBoolean> inHandler = ThreadLocal.withInitial(AtomicBoolean::new);
+   //marker instance used to recognize if a thread is performing a packet handling
+   private static final Object DUMMY = Boolean.TRUE;
+
+   //a thread that has its thread-local map populated with DUMMY is performing a packet handling
+   private static final ThreadLocal<Object> inHandler = new ThreadLocal<>();
 
    public ServerSessionPacketHandler(final ActiveMQServer server,
                                      final CoreProtocolManager manager,
@@ -227,8 +230,25 @@ public class ServerSessionPacketHandler implements ChannelHandler {
       ActiveMQServerLogger.LOGGER.clearingUpSession(session.getName());
    }
 
+   private static void onStartMessagePacketHandler() {
+      assert inHandler.get() != null : "recursion on packet handling is not supported";
+      inHandler.set(DUMMY);
+   }
+
+   private static boolean inHandler() {
+      final Object dummy = inHandler.get();
+      //sanity check: can't exist a thread using a marker different from DUMMY
+      assert ((dummy != null && dummy == DUMMY) || dummy == null) : "wrong marker";
+      return dummy != null;
+   }
+
+   private static void onExitMessagePacketHandler() {
+      assert inHandler.get() == null : "marker not set";
+      inHandler.set(null);
+   }
+
    public void flushExecutor() {
-      if (!inHandler.get().get()) {
+      if (!inHandler()) {
          packetActor.flush();
          callExecutor.flush();
       }
@@ -261,7 +281,7 @@ public class ServerSessionPacketHandler implements ChannelHandler {
       if (logger.isTraceEnabled()) {
          logger.trace("ServerSessionPacketHandler::handlePacket," + packet);
       }
-      inHandler.get().set(true);
+      onStartMessagePacketHandler();
       try {
          final byte type = packet.getType();
          switch (type) {
@@ -287,7 +307,7 @@ public class ServerSessionPacketHandler implements ChannelHandler {
                break;
          }
       } finally {
-         inHandler.get().set(false);
+         onExitMessagePacketHandler();
       }
    }