使用Java模拟操作系统高优先级算法

最近做操作系统的课程设计，网上看到一些动态调度的算法都是基于C写的，下午闲来无事，用Java写了一个高优先级调度的算法玩玩，这个算法首先有这几条要注意

• 优先级是否可以为负的，答案是肯定的，如果有一个线程阻塞了另外一个线程一直去运行就可能一直减去，让优先级变成负数了
• 阻塞的时机：可以说阻塞的时机特别的重要，一旦到达时间需要线程进行阻塞的状态就要立刻将状态改变掉，让它产生调度
• 恢复成就绪状态的问题：因为是有可能是线程进行I/O操作，让其阻塞了，所以说，一个时间片就需要让恢复阻塞的时间常数+1，当变为0的时候让他进入调度状态
• 如果在系统中都是阻塞的线程怎么办？那没有办法，操作系统只能干等着让他们变为就绪状态的时候才能运行

先上一个PCB结构体函数块

public class PCB {
	//进程的ID
	private long id;
	//优先级顺序
	private int priority;
//	运行的cpu时间
	private long cputime;
//  需要运行的时间
	private long alltime;
//  即将阻塞的时间
	private long startblock;
//	从阻塞中回复的时间
	private long blocktime;
//	现在线程的状态
	private String state;
	
	
	public PCB(long id, int priority, long cputime, long alltime,
			long startblock, long blocktime, String state) {
		super();
		this.id = id;
		this.priority = priority;
		this.cputime = cputime;
		this.alltime = alltime;
		this.startblock = startblock;
		this.blocktime = blocktime;
		this.state = state;
	}
	public String getState() {
		return state;
	}
	public void setState(String state) {
		this.state = state;
	}
	public long getBlocktime() {
		return blocktime;
	}
	public void setBlocktime(long blocktime) {
		this.blocktime = blocktime;
	}

//  运行的三个状态
	public final static String STATE_READY = "READY";
	public final static String STATE_RUN = "RUN";
	public final static String STATE_BLOCK = "BLOCK";

	
	
	public long getId() {
		return id;
	}
	public void setId(long id) {
		this.id = id;
	}
	public int getPriority() {
		return priority;
	}
	public void setPriority(int priority) {
		this.priority = priority;
	}
	public long getCputime() {
		return cputime;
	}
	public void setCputime(long cputime) {
		this.cputime = cputime;
	}
	public long getAlltime() {
		return alltime;
	}
	public void setAlltime(long alltime) {
		this.alltime = alltime;
	}
	public long getStartblock() {
		return startblock;
	}
	public void setStartblock(long startblock) {
		this.startblock = startblock;
	}
}

好了，现在是主要的线程调度算法，注意优先级的调整：

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
public class OrderImitate {
	
//  按优先级次序排列的数组
	private ArrayList<PCB> priorityArrayList = null;
	
	
/**
 * 	优先级排序
 */
	public void sortArray(){
		PCB[] pcbs = (PCB[])priorityArrayList.toArray(new PCB[priorityArrayList.size()]);
		Arrays.sort(pcbs, new MyComprator());
		List<PCB> list = Arrays.asList(pcbs);
		this.priorityArrayList = new ArrayList<PCB>(list);
	}
	
/**
 * 	初始化，按照书中的数据进行初始化操作
 */
	private void init(){
		priorityArrayList = new ArrayList<PCB>();
		PCB zero = new PCB(0, 9, 0, 3, 2, 3, PCB.STATE_READY);
		priorityArrayList.add(zero);
		
		PCB one = new PCB(1, 38, 0, 3, -1, 0, PCB.STATE_READY);
		priorityArrayList.add(one);
		
		PCB two = new PCB(2, 30, 0, 6, -1, 0, PCB.STATE_READY);
		priorityArrayList.add(two);
		
		PCB three = new PCB(3, 29, 0, 3, -1, 0, PCB.STATE_READY);
		priorityArrayList.add(three);
		
		PCB four = new PCB(4, 0, 0, 4, -1, 0, PCB.STATE_READY);
		priorityArrayList.add(four);
		
		sortArray();
	}
	
	
/**
 * 优先级执行算法
 * @return
 */
	public boolean hightpPriority(){
		
//		获得第一个元素
		PCB first = priorityArrayList.get(0);
		
		if(!first.getState().equals(PCB.STATE_BLOCK)){
//			运行一次优先级顺序-3
			first.setPriority(first.getPriority()-3);
			first.setCputime(first.getCputime()+1);
			first.setAlltime(first.getAlltime()-1);
//			是否进入阻塞状态
			if(first.getStartblock() > 0){
				first.setStartblock(first.getStartblock() - 1);
			}
//			当是阻塞状态的时候，将状态变为阻塞
			if(first.getStartblock() == 0){
				first.setState(PCB.STATE_BLOCK);
			}
		}
		
//		所需要的时间片完成，结束运行
		if(first.getAlltime() == 0){
			System.out.println("----------------------------------------------");
			System.out.println("ID " + first.getId() + " have done !");
			System.out.println("----------------------------------------------");
			priorityArrayList.remove(0);
		}
		
//		后面的任务优先级+1
		Iterator<PCB> iterator = priorityArrayList.iterator();
		int count = 0;
		while(iterator.hasNext()){
			if(count == 0){
				count++;
				iterator.next();
				continue;
			}
			PCB pcb = iterator.next();
			pcb.setPriority(pcb.getPriority()+1);
//			PCB的阻塞状态改变
			if(pcb.getBlocktime() != 0 && pcb.getState().equals(PCB.STATE_BLOCK)){
				pcb.setBlocktime(pcb.getBlocktime() -1);
				if(pcb.getBlocktime() == 0){
					pcb.setState(PCB.STATE_READY);
				}
			}
		}
		
		sortArray();
		
		return true;
	}
	
	/**
	 * 执行程序
	 */
	public void startRuning(){
		while(hightpPriority()){
			if(this.priorityArrayList.size() == 0){
				System.out.println("-----------------> ALL Works have done !");
				break;
			}
//			输出数据
			Iterator<PCB> iterator = priorityArrayList.iterator();
			System.out.println("-----------------------------------------------------------------------------------------");
			System.out.println("ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE");
			while(iterator.hasNext()){
				PCB pcb = iterator.next();
				System.out
						.printf("%d %8d %12d %12d %13d %14d %18s
", pcb.getId(),
								pcb.getPriority(), pcb.getCputime(),
								pcb.getAlltime(), pcb.getStartblock(),
								pcb.getBlocktime(), pcb.getState());
			}
			System.out.println("-----------------------------------------------------------------------------------------");
		}
	}
	
	public static void main(String[] args) {
		OrderImitate orderImitate = new OrderImitate();
		orderImitate.init();
		orderImitate.startRuning();
	}
	
//	优先级次序调整，优先级高且没有阻塞的进程在前面
	class MyComprator implements Comparator<PCB> {
	    public int compare(PCB o1, PCB o2) {
	    	
			if((o1.getState().equals(PCB.STATE_READY) && o2.getState().equals(PCB.STATE_READY)) || (o1.getState().equals(PCB.STATE_BLOCK) && o2.getState().equals(PCB.STATE_BLOCK))){
				if(o1.getPriority() == o2.getPriority() ){
					return 0;
				}
				else if(o1.getPriority() > o2.getPriority()){
					return -1;
				}else {
					return 1;
				}
			}else if(o1.getState().equals(PCB.STATE_BLOCK) && o2.getState().equals(PCB.STATE_READY)){
				return 1;
			}else{
				return -1; 
			}
			
		}
	}
	
}

一开始是想用优先队列的，但是碰上个问题，如果有多个线程同时进入阻塞状态，那么就可能第二个到后面那个都无法运行，这样没有完全排好序的优先队列就没有办法使用了，而且优先队列碰上一个大的问题，不知道什么，中途修改了队列中的值没有触发队列的排序，导致后面的一系列次序无法进行。

好的，现在看看最后的结果：

-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
1       35            1            2            -1              0              READY
2       31            0            6            -1              0              READY
3       30            0            3            -1              0              READY
0       10            0            3             2              3              READY
4        1            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
1       32            2            1            -1              0              READY
2       32            0            6            -1              0              READY
3       31            0            3            -1              0              READY
0       11            0            3             2              3              READY
4        2            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
----------------------------------------------
ID 1 have done !
----------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       32            0            6            -1              0              READY
3       32            0            3            -1              0              READY
0       12            0            3             2              3              READY
4        3            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
3       33            0            3            -1              0              READY
2       29            1            5            -1              0              READY
0       13            0            3             2              3              READY
4        4            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
3       30            1            2            -1              0              READY
2       30            1            5            -1              0              READY
0       14            0            3             2              3              READY
4        5            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       31            1            5            -1              0              READY
3       27            2            1            -1              0              READY
0       15            0            3             2              3              READY
4        6            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       28            2            4            -1              0              READY
3       28            2            1            -1              0              READY
0       16            0            3             2              3              READY
4        7            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
3       29            2            1            -1              0              READY
2       25            3            3            -1              0              READY
0       17            0            3             2              3              READY
4        8            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
----------------------------------------------
ID 3 have done !
----------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       25            3            3            -1              0              READY
0       18            0            3             2              3              READY
4        9            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       22            4            2            -1              0              READY
0       19            0            3             2              3              READY
4       10            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
0       20            0            3             2              3              READY
2       19            5            1            -1              0              READY
4       11            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
2       20            5            1            -1              0              READY
0       17            1            2             1              3              READY
4       12            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
----------------------------------------------
ID 2 have done !
----------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
0       17            1            2             1              3              READY
4       13            0            4            -1              0              READY
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
4       14            0            4            -1              0              READY
0       14            2            1             0              3              BLOCK
-----------------------------------------------------------------------------------------
可以看到这里因为线程阻塞产生了调度：
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
4       11            1            3            -1              0              READY
0       15            2            1             0              2              BLOCK
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
4        8            2            2            -1              0              READY
0       16            2            1             0              1              BLOCK
-----------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
0       17            2            1             0              0              READY
4        5            3            1            -1              0              READY
-----------------------------------------------------------------------------------------
----------------------------------------------
ID 0 have done !
----------------------------------------------
-----------------------------------------------------------------------------------------
ID      PRIORITY      CPUTIME      ALLTIME      STARTBLOCK      BLOCKTIME      STATE
4        5            3            1            -1              0              READY
-----------------------------------------------------------------------------------------
----------------------------------------------
ID 4 have done !
----------------------------------------------
-----------------> ALL Works have done !

来自为知笔记(Wiz)