我正在尝试在 java 中模拟 CPU 调度算法并使用多线程。我已经成功实现了 FCFS（先到先服务）和 SJF（最短工作优先）。但问题是当我开始想到 SRTF（最短剩余时间优先）时，它是 SJF 的一种抢先形式。我正在使用以下模型：
- CPU 的一个线程，它有一个
CLOCK变量，每个100ms. 我有一个boolean isAvailable;标志让进程在开始执行之前检查 CPU 是否可用。 - Long Term Scheduler(LTS) 的线程，它将进程从进程列表推送到就绪队列。
- Short Term Scheduler (STS) 的线程，它从 ReadyQueue 中获取一个进程并将其分配给 CPU。
- 一旦一个进程被 STS 从 ReadyQueue 中删除以执行，该进程就会检查
isAvailableCPU 的标志。如果true，它将标志设置为 false 并开始执行（为此我只是让线程休眠，(100 * burstTime) ms因为这只是一个模拟）。否则，该过程只是忙于等待：while(CPU.isAvailable != true);。
我事先有进程列表以及它们的到达和突发时间。在我模拟非抢占式调度（FCFS 和 SJF）之前没关系。但是当我尝试使用 SRTF 时，我无法找到一种方法来抢占当前正在运行的进程线程。
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了一个进程，我可以尝试将isAvailable标志设置为false，但是我如何知道最初执行的是哪个线程？而且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该CPU线程。它变得有点乱了。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;
}
}