/*
 * 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.proton.plug.util;

import java.util.concurrent.locks.AbstractQueuedSynchronizer;

public class CreditsSemaphore {

   @SuppressWarnings("serial")
   private static class Sync extends AbstractQueuedSynchronizer {

      public Sync(int initial) {
         setState(initial);
      }

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

      @Override
      public int tryAcquireShared(final int numberOfAqcquires) {
         for (;;) {
            int actualSize = getState();
            int newValue = actualSize - numberOfAqcquires;

            if (newValue < 0) {
               if (actualSize == getState()) {
                  return -1;
               }
            }
            else if (compareAndSetState(actualSize, newValue)) {
               return newValue;
            }
         }
      }

      @Override
      public boolean tryReleaseShared(final int numberOfReleases) {
         for (;;) {
            int actualSize = getState();
            int newValue = actualSize + numberOfReleases;

            if (compareAndSetState(actualSize, newValue)) {
               return true;
            }

         }
      }

      public void setCredits(final int credits) {
         for (;;) {
            int actualState = getState();
            if (compareAndSetState(actualState, credits)) {
               // This is to wake up any pending threads that could be waiting on queued
               releaseShared(0);
               return;
            }
         }
      }
   }

   private final Sync sync;

   public CreditsSemaphore(int initialCredits) {
      sync = new Sync(initialCredits);
   }

   public void acquire() throws InterruptedException {
      sync.acquireSharedInterruptibly(1);
   }

   public boolean tryAcquire() {
      return sync.tryAcquireShared(1) >= 0;
   }

   public void release() throws InterruptedException {
      sync.releaseShared(1);
   }

   public void release(int credits) throws InterruptedException {
      sync.releaseShared(credits);
   }

   public void setCredits(int credits) {
      sync.setCredits(credits);
   }

   public int getCredits() {
      return sync.getCredits();
   }

   public boolean hasQueuedThreads() {
      return sync.hasQueuedThreads();
   }

}