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.test.microbench;
  
  import org.openjdk.jmh.annotations.*;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  
  @BenchmarkMode(Mode.SampleTime)
  @OutputTimeUnit(TimeUnit.NANOSECONDS)
  @Warmup(iterations = 1, time = 1, timeUnit = TimeUnit.SECONDS)
  @Measurement(iterations = 2, time = 10, timeUnit = TimeUnit.SECONDS)
  @Fork(value = 2)
  @Threads(4)
  @State(Scope.Benchmark)
  public class TimedMonitorBench
  {
      @Param({"A", "B"})
      private String type;
  
      private Lock lock;
  
      @State(Scope.Thread)
      public static class ThreadState
      {
          Lock lock;
  
          @Setup(Level.Iteration)
          public void setup(TimedMonitorBench benchState) throws Throwable
          {
              if (benchState.type.equals("A")) lock = new A();
              else if (benchState.type.equals("B")) lock = new B();
              else throw new IllegalStateException();
          }
      }
  
      @Setup(Level.Trial)
      public void setup() throws Throwable
      {
          if (type.equals("A")) lock = new A();
          else if (type.equals("B")) lock = new B();
          else throw new IllegalStateException();
      }
  
      interface Lock
      {
          boolean lock(long deadline);
          void maybeUnlock();
      }
  
      static class A implements Lock
      {
          private volatile Thread lockedBy;
          private volatile int waiting;
  
          private static final AtomicReferenceFieldUpdater<A, Thread> lockedByUpdater = AtomicReferenceFieldUpdater.newUpdater(A.class, Thread.class, "lockedBy");
  
          public boolean lock(long deadline)
          {
              try
              {
                  Thread thread = Thread.currentThread();
                  if (lockedByUpdater.compareAndSet(this, null, thread))
                      return true;
  
                  synchronized (this)
                  {
                      waiting++;
  
                      try
                      {
                          while (true)
                          {
                              if (lockedByUpdater.compareAndSet(this, null, thread))
                                  return true;
  
                              while (lockedBy != null)
                              {
                                  long now = System.nanoTime();
                                  if (now >= deadline)
                                      return false;
  
                                  wait(1 + ((deadline - now) - 1) / 1000000);
                              }
                          }
                      }
                      finally
                      {
                          waiting--;
                      }
                  }
              }
              catch (InterruptedException e)
              {
                  Thread.currentThread().interrupt();
                  return false;
              }
          }
  
          public void maybeUnlock()
          {
              // no visibility requirements, as if we hold the lock it was last updated by us
              if (lockedBy == null)
                  return;
  
              Thread thread = Thread.currentThread();
  
              if (lockedBy == thread)
              {
                  lockedBy = null;
                  if (waiting > 0)
                  {
                      synchronized (this)
                      {
                          notify();
                      }
                  }
              }
          }
      }
  
      static class B implements Lock
      {
          private Thread lockedBy;
  
          public synchronized boolean lock(long deadline)
          {
              try
              {
                  Thread thread = Thread.currentThread();
                  while (lockedBy != null)
                  {
                      long now = System.nanoTime();
                      if (now >= deadline)
                          return false;
  
                      wait(1 + ((deadline - now) - 1) / 1000000);
                  }
                  lockedBy = thread;
                  return true;
              }
              catch (InterruptedException e)
              {
                  Thread.currentThread().interrupt();
                  return false;
              }
          }
  
          public void maybeUnlock()
          {
              // no visibility requirements, as if we hold the lock it was last updated by us
              if (lockedBy == null)
                  return;
  
              Thread thread = Thread.currentThread();
  
              if (lockedBy == thread)
              {
                  synchronized (this)
                  {
                      lockedBy = null;
                      notify();
                  }
              }
          }
      }
  
      @Benchmark
      public void unshared(ThreadState state)
      {
          state.lock.lock(Long.MAX_VALUE);
          state.lock.maybeUnlock();
      }
  
      @Benchmark
      public void shared()
      {
          lock.lock(Long.MAX_VALUE);
          lock.maybeUnlock();
      }
  }
  