/* -*- tab-width: 4 -*-
*
* Electric(tm) VLSI Design System
*
* File: DEQueue.java
* Written by Team 7: Felix Schmidt, Daniel Lechner
*
* This code has been developed at the Karlsruhe Institute of Technology (KIT), Germany,
* as part of the course "Multicore Programming in Practice: Tools, Models, and Languages".
* Contact instructor: Dr. Victor Pankratius (pankratius@ipd.uka.de)
*
* Copyright (c) 2010 Sun Microsystems and Static Free Software
*
* 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.placement.forceDirected2.utils.concurrent;
import java.util.concurrent.atomic.AtomicReference;
/**
*
* Parallel Placement
*
* <br />
* <b>How to use this class?</b> <br />
* This class is intentionaly implemented for work stealing. It provides a add
* and get method. This methods works like a stack. add pushes a item into the
* queue and get retrieves this item in a LIFO way. Work stealing needs a double
* ended version of a queue or stack. So this class provides also a getFromTop
* method. This method returns a element from the top of the stack. In addition
* with the add method this class works like a FIFO queue.
*
* @param <T>
* type of elements
*/
public class DEQueue<T> extends IDEStructure<T> {
// start capcacity of the circular array
// the array uses: 1 << LOG_CAPCITY
// for LOG_CAPACITY = 4: 1 << 4: b10000 = d16
private final static int LOG_CAPACITY = 4;
private volatile CircularArray items;
private volatile int bottom;
private AtomicReference<Integer> top;
/**
* Constructor
*/
public DEQueue() {
this.items = new CircularArray(LOG_CAPACITY);
this.top = new AtomicReference<Integer>(Integer.valueOf(0));
this.bottom = 0;
}
/**
* add a element at the bottom
*/
@Override
public void add(T item) {
int oldBottom = this.bottom;
int oldTop = this.top.get().intValue();
CircularArray currentTasks = this.items;
int size = oldBottom - oldTop;
if (size >= currentTasks.getCapacity() - 1) {
currentTasks = currentTasks.resize(oldBottom, oldTop);
this.items = currentTasks;
}
this.items.add(oldBottom, (Runnable) item);
this.bottom = oldBottom + 1;
this.size = new Integer(this.size.intValue() + 1);
}
/**
* retrieves a element from the bottom
*/
@SuppressWarnings("unchecked")
@Override
public T get() throws EmptyException {
this.bottom--;
int oldTop = this.top.get().intValue();
int newTop = oldTop + 1;
int size = this.bottom - oldTop;
if (size < 0) {
this.bottom = oldTop;
return null;
}
T item = (T) this.items.get(this.bottom);
if (size > 0) {
this.size = new Integer(this.size.intValue() - 1);
return item;
}
if (!this.top.compareAndSet(new Integer(oldTop), new Integer(newTop))) {
item = null;
}
this.bottom = oldTop + 1;
this.size = new Integer(this.size.intValue() - 1);
return item;
}
/**
* @return element from the top
*/
@SuppressWarnings("unchecked")
@Override
public T getFromTop() throws EmptyException {
int oldTop = this.top.get().intValue();
int newTop = oldTop + 1;
int oldBottom = this.bottom;
int size = oldBottom - oldTop;
if (size <= 0) {
return null;
}
T item = (T) this.items.get(oldTop);
if (this.top.compareAndSet(new Integer(oldTop), new Integer(newTop))) {
this.size = new Integer(this.size.intValue() - 1);
return item;
}
return null;
}
@Override
public boolean isEmpty() {
int localTop = this.top.get().intValue();
int localBottom = this.bottom;
return (localBottom <= localTop);
}
}