/*
 *  This file is part of the Jikes RVM project (http://jikesrvm.org).
 *
 *  This file is licensed to You under the Eclipse Public License (EPL);
 *  You may not use this file except in compliance with the License. You
 *  may obtain a copy of the License at
 *
 *      http://www.opensource.org/licenses/eclipse-1.0.php
 *
 *  See the COPYRIGHT.txt file distributed with this work for information
 *  regarding copyright ownership.
 */
package org.mmtk.utility.deque;

import org.mmtk.utility.Constants;

import org.mmtk.vm.VM;

import org.vmmagic.unboxed.*;
import org.vmmagic.pragma.*;

/**
 * This supports <i>unsynchronized</i> enqueuing and dequeuing of
 * address pairs
 */
@Uninterruptible public class AddressPairDeque extends LocalDeque implements Constants {

  /****************************************************************************
   *
   * Public instance methods
   */

  /**
   * Constructor
   *
   * @param queue The shared queue to which this queue will append
   * its buffers (when full or flushed) and from which it will aquire new
   * buffers when it has exhausted its own.
   */
  public AddressPairDeque(SharedDeque queue) {
    super(queue);
  }

  /**
   * Insert an address pair into the address queue.
   *
   * @param addr1 the first address to be inserted into the address queue
   * @param addr2 the second address to be inserted into the address queue
   */
  public final void insert(Address addr1, Address addr2) {
    if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!addr1.isZero());
    if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!addr2.isZero());
    checkTailInsert(2);
    uncheckedTailInsert(addr1);
    uncheckedTailInsert(addr2);
  }

  /**
   * Push an address pair onto the address queue.
   *
   * @param addr1 the first value to be pushed onto the address queue
   * @param addr2 the second value to be pushed onto the address queue
   */
  public final void push(Address addr1, Address addr2) {
    if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!addr1.isZero());
    if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!addr2.isZero());
    checkHeadInsert(2);
    uncheckedHeadInsert(addr2);
    uncheckedHeadInsert(addr1);
  }

  /**
   * Pop the first address in a pair from the address queue, return
   * zero if the queue is empty.
   *
   * @return The next address in the address queue, or zero if the
   * queue is empty
   */
  public final Address pop1() {
    if (checkDequeue(2))
      return uncheckedDequeue();
    else
      return Address.zero();
  }

  /**
   * Pop the second address in a pair from the address queue.
   *
   * @return The next address in the address queue
   */
  public final Address pop2() {
    return uncheckedDequeue();
  }

  public final boolean isEmpty() {
    return !checkDequeue(2);
  }
}