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.cassandra.utils.concurrent;
  
  import java.util.concurrent.TimeUnit;
  
  import org.apache.cassandra.utils.Intercept;
  import org.apache.cassandra.utils.Shared;
  
  import static org.apache.cassandra.utils.Clock.Global.nanoTime;
  import static org.apache.cassandra.utils.Shared.Scope.SIMULATION;
  
  @Shared(scope = SIMULATION)
  public interface Semaphore
  {
      /**
       * @return the number of permits presently in this semaphore
       */
      int permits();
  
      /**
       * set the number of permits in this semaphore to zero
       */
      int drain();
  
      /**
       * Increase the number of available permits and signal any waiters that may be served by the release
       */
      void release(int permits);
  
      /**
       * Try to take permits, returning immediately
       * @return true iff permits acquired
       */
      boolean tryAcquire(int acquire);
  
      /**
       * Try to take permits, waiting up to timeout
       * @return true iff permits acquired
       * @throws InterruptedException if interrupted
       */
      boolean tryAcquire(int acquire, long time, TimeUnit unit) throws InterruptedException;
  
      /**
       * Try to take permits, waiting until the deadline
       * @return true iff permits acquired
       * @throws InterruptedException if interrupted
       */
      boolean tryAcquireUntil(int acquire, long nanoTimeDeadline) throws InterruptedException;
  
      /**
       * Take permits, waiting indefinitely until available
       * @throws InterruptedException if interrupted
       */
      void acquire(int acquire) throws InterruptedException;
  
      /**
       * Take permits, waiting indefinitely until available
       * @throws UncheckedInterruptedException if interrupted
       */
      void acquireThrowUncheckedOnInterrupt(int acquire) throws UncheckedInterruptedException;
  
      /**
       * Factory method used to capture and redirect instantiations for simulation
       *
       * Construct an unfair Semaphore initially holding the specified number of permits
       */
      @Intercept
      public static Semaphore newSemaphore(int permits)
      {
          return new Standard(permits, false);
      }
  
      /**
       * Factory method used to capture and redirect instantiations for simulation
       *
       * Construct a fair Semaphore initially holding the specified number of permits
       */
      @Intercept
      public static Semaphore newFairSemaphore(int permits)
      {
          return new Standard(permits, true);
      }
  
      public static class Standard extends java.util.concurrent.Semaphore implements Semaphore
      {
          private static final long serialVersionUID = 0;  // for simulator support
          public Standard(int permits)
          {
              this(permits, false);
          }
  
          public Standard(int permits, boolean fair)
          {
              super(permits, fair);
          }
  
          /**
           * {@link Semaphore#drain()}
           */
          public int drain()
          {
              return drainPermits();
          }
  
          /**
           * Number of permits that are available to be acquired. {@link Semaphore#permits()}
           */
          public int permits()
          {
              return availablePermits();
          }
  
          /**
           * Number of permits that have been acquired in excess of available. {@link Semaphore#permits()}
           */
          public int waiting()
          {
              return getQueueLength();
          }
  
          /**
           * {@link Semaphore#tryAcquireUntil(int, long)}
           */
          public boolean tryAcquireUntil(int acquire, long nanoTimeDeadline) throws InterruptedException
          {
              long wait = nanoTimeDeadline - nanoTime();
              return tryAcquire(acquire, Math.max(0, wait), TimeUnit.NANOSECONDS);
          }
  
          @Override
          public void acquireThrowUncheckedOnInterrupt(int acquire) throws UncheckedInterruptedException
          {
              try
              {
                  acquire(acquire);
              }
              catch (InterruptedException e)
              {
                  throw new UncheckedInterruptedException(e);
              }
          }
      }
  }
  