com.sun.electric.tool.util.concurrent.datastructures.BDEQueue Maven / Gradle / Ivy
/* -*- tab-width: 4 -*-
*
* Electric(tm) VLSI Design System
*
* File: BDEQueue.java
*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
*
* Electric(tm) is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* Electric(tm) is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Electric(tm); see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, Mass 02111-1307, USA.
*/
package com.sun.electric.tool.util.concurrent.datastructures;
import java.util.List;
import java.util.concurrent.atomic.AtomicStampedReference;
import com.sun.electric.tool.util.concurrent.utils.ConcurrentCollectionFactory;
/**
*
* Bounded double ended queue
*
* @param
*
* @author Felix Schmidt
*/
public class BDEQueue extends IDEStructure {
private List objects;
private volatile int bottom;
private AtomicStampedReference top;
private int capacity;
private volatile int amount;
/**
* Constructor
*
* @param capacity
* of bounded double ended queue
*/
public BDEQueue(int capacity) {
objects = ConcurrentCollectionFactory.createArrayList();
top = new AtomicStampedReference(0, 0);
this.capacity = capacity;
bottom = 0;
amount = 0;
}
/**
* @return element from the top of the data structure
*/
@Override
public T getFromTop() {
int[] stamp = new int[1];
int oldTop = top.get(stamp);
int newTop = oldTop + 1;
int oldStamp = stamp[0];
int newStamp = oldStamp + 1;
if (bottom <= oldTop)
return null;
T tmp = objects.get(oldTop);
if (top.compareAndSet(oldTop, newTop, oldStamp, newStamp)) {
amount--;
return tmp;
}
return null;
}
/**
* Add a item to the data structure
*/
@Override
public void add(T item) {
this.tryAdd(item);
}
/**
* return true if the data structure is empty; otherwise false
*/
@Override
public boolean isEmpty() {
return !(top.getReference() < bottom);
}
@Override
public T remove() {
if (bottom == 0) {
return null;
}
bottom--;
T tmp = objects.get(bottom);
int[] stamp = new int[1];
int oldTop = top.get(stamp);
int newTop = oldTop + 1;
int oldStamp = stamp[0];
int newStamp = oldStamp + 1;
if (bottom > oldTop) {
amount--;
return tmp;
}
if (bottom == oldTop) {
bottom = 0;
if (top.compareAndSet(oldTop, newTop, oldStamp, newStamp)) {
amount--;
return tmp;
}
}
top.set(newTop, newStamp);
return null;
}
@Override
public boolean isFull() {
return (amount == capacity);
}
public boolean tryAdd(T item) {
if (this.isFull())
return false;
objects.add(item);
bottom++;
amount++;
return true;
}
}