code: /*
   * Copyright (c) 2017-2018 The Regents of the University of California
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   * 1. Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package edu.berkeley.cs.jqf.instrument.util;
  
  /**
   * A blocking queue for single-producer and single-consumer where the producer and
   * consumer never change and are distinct threads.
   *
   * This allows reading and writing from the queue without using system
   * locks. The only synchronization is via {@code volatile} pointers for the producer
   * and consumer in a fixed-size circular buffer.
   *
   * Reading from an empty queue and writing to a full queue results in a spinning wait,
   * and therefore the producer and consumer <em>must</em> be distinct in order to avoid
   * deadlocks.
   *
   * @author Rohan Padhye
   */
  public final class FastBlockingQueue<T> {
      private final int size;
      private final Object[] buffer;
      private volatile int producer = 0;
      private volatile int consumer = 0;
  
      public FastBlockingQueue(int size) {
          this.size = size;
          this.buffer = new Object[size];
      }
  
      private int increment(int idx) {
          return (idx + 1) % size;
      }
  
      public final boolean isEmpty() {
          return producer == consumer;
      }
  
      public final boolean isFull() {
          return increment(producer) == consumer;
      }
  
      public final void put(T item) {
          while (isFull()) {
              // Spin-block
          }
          buffer[producer] = item;
          producer = increment(producer);
      }
  
      public final T remove(long timeout) {
          long ticks = 0;
          while(isEmpty()) {
              if (++ticks > timeout) {
                  return null;
              }
          }
          @SuppressWarnings("unchecked")
          T item = (T) buffer[consumer];
          consumer = increment(consumer);
          return item;
      }
  }
  