最短剩余时间优先：Java 多线程

Question

我正在尝试在 java 中模拟 CPU 调度算法并使用多线程。我已经成功地实施了FCFS（先到先得）和SJF（最短的工作优先）。但问题是当我开始想到SRTF（最短剩余时间优先）时，它是SJF的一种先发制人的形式。我正在使用以下模型：

• CPU的线程，它有一个CLOCK变量，它每100ms保持滴答声（一个简单的时钟增量）。我有一个布尔值is的；标志，用于在开始执行之前检查CPU是否可用。
• 长期调度程序（LTS）的线程，它将进程从进程列表推送到就绪队列。
• 短期调度程序（STS）的线程，它从ReadyQueue获取一个进程并将其分配给CPU。
• 一旦STS从ReadyQueue中删除了一个进程以供执行，该进程就会检查CPU的is

我手头有进程列表以及它们的到达和爆发时间。这是确定的，直到我模拟非抢占式调度(FCFS和SJF)。但是当我尝试SRTF时，我无法找到抢占当前正在运行的进程线程的方法。

对于 SRTF，我知道从 ReadyQueue 中选择下一个进程的方法。一旦我从队列中选择一个进程，我就可以尝试将 isAvailable 标志设置为 false，但是我如何知道最初正在执行哪个线程？由于我没有使用太多同步黑白线程，因此我将有多个进程使用 CPU 线程。它变得有点混乱。请帮忙。谢谢！

这是进程的代码：

enum State {ARRIVED, WAITING, READY, RUNNING, EXECUTED}
public class Process implements Runnable
{
    int pid;
    int arrTime;
int burstTime;
int priority;
long startTime;
long endTime;
State procState = null;

Process(int pid, int arrTime, int burstTime, int priority)
{
    this.pid = pid;
    this.arrTime = arrTime;
    this.burstTime = burstTime;
    this.priority = priority;
    this.procState = State.ARRIVED;
    this.startTime = 0;


    this.endTime = 0;    /* I also considered adding a timeElapsedUnderExecution
 attribute to the process. So I can check after every cycle if the CPU is still available
 and keep incrementing the time elapsed. Once the timeElapsed becomes same as burstTime, i
 stop the process. Or if after a cycle, the CPU is not available, i know from where to
 resume my Process. Is this the way to go ? */

    }

boolean isReady()
{
    if((this.arrTime <= CPU.CLOCK) && (this.procState == State.ARRIVED))
        return true;
    else return false;
}

@Override
public void run() {
    // TODO Auto-generated method stub
    if(this.procState == State.READY)
        this.procState = State.WAITING;

    while(!CPU.isAvailable());

    try 
    {
        this.procState = State.RUNNING;
        System.out.println("Process " + pid + " executing...");
        this.startTime = CPU.CLOCK;
        System.out.println("Process " + this.pid + ": Begins at " + this.startTime);
        Thread.sleep(this.burstTime * 100);
        this.endTime = CPU.CLOCK;
        System.out.println("Process " + this.pid + ": Ends at " + this.endTime);
        this.procState = State.EXECUTED;

    }
    catch (InterruptedException e) 
    {
        // TODO Auto-generated catch block
        System.out.println("Interrupted: " + pid);
        e.printStackTrace();
    }
    }
}

CPU的代码:

    import java.util.LinkedList;
    import java.util.Queue;

    public class CPU implements Runnable

{
    static Long CLOCK = new Long(0);
    static LinkedList<Process> ReadyQ = new LinkedList<Process>();
private static boolean isAvailable = true;
static boolean done = false;

public static boolean isAvailable() {
    return isAvailable;
}

public static void setAvailable(boolean isAvailable) {
    CPU.isAvailable = isAvailable;
}

static void incrementCLOCK()
{
    LTS.checkArrival();
    CPU.CLOCK++;
    try {
        Thread.sleep(100);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println("Clock Tick: " + CPU.CLOCK);
}

@Override
public void run() {
    // TODO Auto-generated method stub
    System.out.println("CPU starts.!!!");
    while(CPU.done != true)
        synchronized(CPU.CLOCK)
        {
            incrementCLOCK();
            }
    }
}

LTS 的代码：

public class LTS implements Runnable 
{
    private static Process[] pList = null;
    private final int NUM;
    static Integer procStarted;
    static Integer procFinished;
    static boolean STSDone = false;


LTS(Process[] pList, int num)
{
    this.NUM = num;
    LTS.pList = pList;
}

static void checkArrival()
{
    if(pList == null) return;
    for(int i = 0; i < pList.length; i++)
        if(pList[i].isReady())
        {
            pList[i].procState = State.READY;
            System.out.println("Process " + pList[i].pid + " is now ready.");
            CPU.ReadyQ.add(pList[i]);
        }
}

@Override
public void run() {
    // TODO Auto-generated method stub
    System.out.println("Long Term Scheduler starts.!!!");
    while(LTS.STSDone != true)
    {
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    System.out.println(LTS.STSDone);
    System.out.println("LTS ends.!!!");
        CPU.done = true;
    }
}




Answer 1

问题1是您的共享状态不是线程安全的。即使是布尔值这样的简单事情也需要正确的线程原语来确保跨线程的可见性（又名“易失性”）。