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Processor Scheduling - Shortest Remaining Time First (SRTF) 最短剩余时间优先调度算法(抢占式)
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'use strict'; | |
// Shortest Remaining Time First (SRTF) Algorithm 最短剩余时间优先调度算法(抢占式) | |
let processes = [ | |
['P1', 10, 0], | |
['P2', 1, 1], | |
['P3', 5, 2], | |
['P4', 1, 3], | |
['P5', 2, 4] | |
], // [进程名,运行时间,到达输入井时间(从0ms开始)] | |
readyQueue = [], // 就绪队列 | |
running = null, // 运行中的进程 | |
runningStart = 0, // 运行中的进程开始时间 | |
globalTimer = 0, // 全局时间 | |
finishTime = {}, // 进程完成时间 | |
illustrations = {}; // 直观化输出 | |
function illustrate(name, pos, chr) { // 制作直观化输出 | |
if (!illustrations[name]) illustrations[name] = []; | |
let arr = illustrations[name]; | |
for (let i = 0; i < pos; i++) { // 填充数组中间的空部分 | |
if (!arr[i]) arr[i] = '-'; | |
} | |
arr[pos] = chr; | |
} | |
while (true) { | |
let schFlag = false; // 抢占调度标志 | |
for (let i = 0, len = processes.length; i < len; i++) { // 模拟进程按不同时间到达就绪队列 | |
let [name, spend, arrivalTime] = processes[i]; | |
if (arrivalTime <= globalTimer) { | |
let currentRemaingTime = running ? running.spend - running.finished : 0; // 获得当前进程的剩余时间 | |
processes.splice(i, 1); | |
illustrate(name, globalTimer, '|'); // 用竖线标记到达时间 | |
readyQueue.push({ | |
name: name, // 进程信息 | |
spend: spend, // 运行时间 | |
arrivalTime: arrivalTime, // 到达就绪队列时间 | |
finished: 0 // 进程已经执行的时间 | |
}); | |
if (spend <= currentRemaingTime) { // 如果新加入就绪队列的进程剩余时间小于当前进程的剩余时间,抢占当前进程 | |
schFlag = true; | |
} | |
i--; | |
len--; | |
} | |
} | |
if (processes.length === 0 && readyQueue.length === 0 && !running) { | |
break; | |
} | |
// -----------以下部分模拟的是调度程序 | |
if (!running) { | |
// 按最短剩余时间排序从小到大排序 | |
readyQueue.sort((a, b) => (a.spend - a.finished) - (b.spend - b.finished)); | |
running = readyQueue.shift(); | |
runningStart = globalTimer; | |
illustrate(running.name, globalTimer, '#'); | |
} else { | |
let { name, spend, finished, arrivalTime } = running; | |
if (finished >= spend) { // 进程已经执行完毕 | |
running = null; | |
finishTime[name] = [arrivalTime, globalTimer - arrivalTime]; // [程序到达时间,周转时间] | |
continue; // 在当前进程完成的瞬间调度下一个进程,不要等globalTimer++ | |
} else if (schFlag) { // 就绪队列加入了剩余时间更短的进程,被抢占 | |
readyQueue.push(running); | |
running = null; | |
continue; // 在当前进程移走的瞬间调度下一个进程,不要等globalTimer++ | |
} else { | |
illustrate(name, globalTimer, '#'); | |
} | |
} | |
running.finished++; | |
globalTimer++; | |
} | |
console.log('All Processes are Completed.'); | |
let sum = 0, | |
processNum = 0; | |
for (let i in illustrations) { | |
let [arrivalTime, turn] = finishTime[i]; | |
sum += turn; | |
processNum++; | |
console.log(`${i} ${illustrations[i].join('')} %c${turn}ms (Arrive at ${arrivalTime}ms)`, 'color:#585858'); | |
} | |
let average = sum / processNum; | |
console.log(`Average Turnaround Time: ${average}ms`); |
这个是抢占式调度算法
- 这是一个
抢占式
(也有非抢占式
)算法 - 适用于
进程调度
和作业调度
- 会造成进程饥饿
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其实就是短作业优先调度算法(
SJN
或SJF
)的抢占式,SRTF也称抢占式短作业优先调度算法