artemis-commons/src/main/java/org/apache/activemq/artemis/utils/actors/HandlerBase.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.activemq.artemis.utils.actors;

/**
 * This abstract class will encapsulate
 * ThreadLocals to determine when a class is a handler.
 * This is because some functionality has to be avoided if inHandler().
 *
 */
public abstract class HandlerBase {

   private static class Counter {
      int count = 1;
   }

   /** an actor could be used within an OrderedExecutor. So we need this counter to decide if there's a Handler anywhere in the stack trace */
   private static final ThreadLocal<Counter> counterThreadLocal = new ThreadLocal<>();

   protected static void enter() {
      Counter counter = counterThreadLocal.get();
      if (counter == null) {
         counter = new Counter(); // it starts at 1, so no need to increment it
         counterThreadLocal.set(counter);
      } else {
         counter.count++;
      }
   }

   public static boolean inHandler() {
      Counter counter = counterThreadLocal.get();
      if (counter == null) {
         return false;
      } else if (counter.count == 0) {
         counterThreadLocal.remove();
      }
      return counter.count > 0;
   }

   protected static void leave() {
      Counter counter = counterThreadLocal.get();
      if (counter != null) {
         if (--counter.count <= 0) {
            counterThreadLocal.remove();
         }
      }
   }

}