code: /**
   * 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 edu.utexas.cs.utopia.cortado.githubbenchmarks.org.apache.hadoop.metrics2.impl;
  
  import java.util.ConcurrentModificationException;
  
  /**
   * A half-blocking (nonblocking for producers, blocking for consumers) queue
   * for metrics sinks.
   *
   * New elements are dropped when the queue is full to preserve "interesting"
   * elements at the onset of queue filling events
   */
  class SinkQueue<T> {
  
      interface Consumer<T> {
          void consume(T object) throws InterruptedException;
      }
  
      // A fixed size circular buffer to minimize garbage
      private final T[] data;
      private int head; // head position
      private int tail; // tail position
      private int size; // number of elements
      private Thread currentConsumer = null;
  
      @SuppressWarnings("unchecked")
      SinkQueue(int capacity) {
          this.data = (T[]) new Object[Math.max(1, capacity)];
          head = tail = size = 0;
      }
  
      synchronized boolean enqueue(T e) {
          if (data.length == size) {
              return false;
          }
          ++size;
          tail = (tail + 1) % data.length;
          data[tail] = e;
          notify();
          return true;
      }
  
      /**
       * Consume one element, will block if queue is empty
       * Only one consumer at a time is allowed
       * @param consumer  the consumer callback object
       */
      void consume(Consumer<T> consumer) throws InterruptedException {
          T e = waitForData();
  
          try {
              consumer.consume(e);  // can take forever
              _dequeue();
          }
          finally {
              clearConsumerLock();
          }
      }
  
      /**
       * Consume all the elements, will block if queue is empty
       * @param consumer  the consumer callback object
       * @throws InterruptedException
       */
      void consumeAll(Consumer<T> consumer) throws InterruptedException {
          waitForData();
  
          try {
              for (int i = size(); i-- > 0; ) {
                  consumer.consume(front()); // can take forever
                  _dequeue();
              }
          }
          finally {
              clearConsumerLock();
          }
      }
  
      /**
       * Dequeue one element from head of the queue, will block if queue is empty
       * @return  the first element
       * @throws InterruptedException
       */
      synchronized T dequeue() throws InterruptedException {
          checkConsumer();
  
          while (0 == size) {
              wait();
          }
          return _dequeue();
      }
  
      private synchronized T waitForData() throws InterruptedException {
          checkConsumer();
  
          while (0 == size) {
              wait();
          }
          setConsumerLock();
          return front();
      }
  
      private synchronized void checkConsumer() {
          if (currentConsumer != null) {
              throw new ConcurrentModificationException("The "+
                      currentConsumer.getName() +" thread is consuming the queue.");
          }
      }
  
      private synchronized void setConsumerLock() {
          currentConsumer = Thread.currentThread();
      }
  
      private synchronized void clearConsumerLock() {
          currentConsumer = null;
      }
  
      private synchronized T _dequeue() {
          if (0 == size) {
              throw new IllegalStateException("Size must > 0 here.");
          }
          --size;
          head = (head + 1) % data.length;
          T ret = data[head];
          data[head] = null;  // hint to gc
          return ret;
      }
  
      synchronized T front() {
          return data[(head + 1) % data.length];
      }
  
      synchronized T back() {
          return data[tail];
      }
  
      synchronized void clear() {
          checkConsumer();
  
          for (int i = data.length; i-- > 0; ) {
              data[i] = null;
          }
          size = 0;
      }
  
      synchronized int size() {
          return size;
      }
  
      int capacity() {
          return data.length;
      }
  }