content: /*
   * 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 = 0;
     }
  
     // There is only going to be a single Thread using the counter, so it is safe to cache this instance
     private final Counter cachedCounter = new Counter();
  
     /**
      * 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 void enter() {
        Counter counter = counterThreadLocal.get();
        if (counter == null) {
           cachedCounter.count = 1;
           counterThreadLocal.set(cachedCounter);
        } else {
           counter.count++;
        }
     }
  
     public boolean inHandler() {
        Counter counter = counterThreadLocal.get();
        if (counter == null) {
           return false;
        } else if (counter.count == 0) {
           counterThreadLocal.remove();
        }
        return counter.count > 0;
     }
  
     protected void leave() {
        Counter counter = counterThreadLocal.get();
        if (counter != null && --counter.count <= 0) {
           counterThreadLocal.remove();
        }
     }
  
  }
  