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This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

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/*
 * 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;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;

/**
 * This class will use the framework provided to by AbstractQueuedSynchronizer.
 * AbstractQueuedSynchronizer is the framework for any sort of concurrent synchronization, such as Semaphores, events, etc, based on AtomicIntegers.
 *
 * This class works just like CountDownLatch, with the difference you can also increase the counter
 *
 * It could be used for sync points when one process is feeding the latch while another will wait when everything is done. (e.g. waiting IO completions to finish)
 *
 * On ActiveMQ Artemis we have the requirement of increment and decrement a counter until the user fires a ready event (commit). At that point we just act as a regular countDown.
 *
 * Note: This latch is reusable. Once it reaches zero, you can call up again, and reuse it on further waits.
 *
 * For example: prepareTransaction will wait for the current completions, and further adds will be called on the latch. Later on when commit is called you can reuse the same latch.
 */
public class ReusableLatch {

   /**
    * Look at the doc and examples provided by AbstractQueuedSynchronizer for more information
    *
    * @see AbstractQueuedSynchronizer
    */
   @SuppressWarnings("serial")
   private static class CountSync extends AbstractQueuedSynchronizer {

      private CountSync(int count) {
         setState(count);
      }

      public int getCount() {
         return getState();
      }

      public void setCount(final int count) {
         setState(count);
      }

      @Override
      public int tryAcquireShared(final int numberOfAqcquires) {
         return getState() == 0 ? 1 : -1;
      }

      public void add() {
         for (;;) {
            int actualState = getState();
            int newState = actualState + 1;
            if (compareAndSetState(actualState, newState)) {
               return;
            }
         }
      }

      @Override
      public boolean tryReleaseShared(final int numberOfReleases) {
         for (;;) {
            int actualState = getState();
            if (actualState == 0) {
               return true;
            }

            int newState = actualState - numberOfReleases;

            if (newState < 0) {
               newState = 0;
            }

            if (compareAndSetState(actualState, newState)) {
               return newState == 0;
            }
         }
      }
   }

   private final CountSync control;

   public ReusableLatch() {
      this(0);
   }

   public ReusableLatch(final int count) {
      control = new CountSync(count);
   }

   public int getCount() {
      return control.getCount();
   }

   public void setCount(final int count) {
      control.setCount(count);
   }

   public void countUp() {
      control.add();
   }

   public void countDown() {
      control.releaseShared(1);
   }

   public void countDown(final int count) {
      control.releaseShared(count);
   }

   public void await() throws InterruptedException {
      control.acquireSharedInterruptibly(1);
   }

   public boolean await(final long milliseconds) throws InterruptedException {
      return control.tryAcquireSharedNanos(1, TimeUnit.MILLISECONDS.toNanos(milliseconds));
   }

   public boolean await(final long timeWait, TimeUnit timeUnit) throws InterruptedException {
      return control.tryAcquireSharedNanos(1, timeUnit.toNanos(timeWait));
   }
}