文章目錄

• 一、FCFS的介紹
• 二、代碼演示
• 三、代碼分析
• • 1.使用節(jié)點(diǎn)模擬進(jìn)程
  • 2.SimulateFCFS（核心模擬FCFS類(lèi)）
  • 3.創(chuàng)建一個(gè)節(jié)點(diǎn)為n的隊(duì)列（模擬就緒隊(duì)列）
  • 4.核心計(jì)算分析
  • 5.輸入到達(dá)時(shí)間和服務(wù)時(shí)間（模擬進(jìn)程到達(dá)和服務(wù))
  • 6.出隊(duì)列（模擬完成所有進(jìn)程工作）

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一、FCFS的介紹

先來(lái)先服務(wù)的調(diào)度算法：最簡(jiǎn)單的調(diào)度算法，既可以用于作業(yè)調(diào)度 ，也可以用于程序調(diào)度，當(dāng)作業(yè)調(diào)度中采用該算法時(shí)，系統(tǒng)將按照作業(yè)到達(dá)的先后次序來(lái)進(jìn)行調(diào)度，優(yōu)先從后備隊(duì)列中，選擇一個(gè)或多個(gè)位于隊(duì)列頭部的作業(yè)，把他們調(diào)入內(nèi)存，分配所需資源、創(chuàng)建進(jìn)程，然后放入“就緒隊(duì)列”,直到該進(jìn)程運(yùn)行到完成或發(fā)生某事件堵塞后，進(jìn)程調(diào)度程序才將處理機(jī)分配給其他進(jìn)程。

簡(jiǎn)單了說(shuō)就是如同名字 “先來(lái)先服務(wù)” ；

二、代碼演示

package com.zsh.blog;import java.util.Scanner;/*** @author:抱著魚(yú)睡覺(jué)的喵喵* @date:2021/3/19* @description:*/ public class SimulateSystem {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);SimulateFCFS simulateFCFS = new SimulateFCFS();boolean flag = true;char at = ' ';System.out.println("a:Simulate multiple processes to form a queue");System.out.println("b:Assign a process to the queue");System.out.println("d:Complete all process work");System.out.println("e:Exit the simulated system");while (flag) {System.out.println("Please enter your instructions：");at = scanner.next().charAt(0);switch (at) {case 'a':simulateFCFS.createQueue();break;case 'b':simulateFCFS.assignProcess();break;case 'd':simulateFCFS.finishAllProcessTask();return;case 'e':System.out.println("Simulated is end~");return;default:System.out.println("Your input is wrong, please re-enter！");break;}}}}class Queue {int arrTime; //timeOfArrivalint serviceTime; //timeOfServiceint finishTime; //timeOfComplishint turnTime; //timeOfTurnarounddouble weightTurnTime; //timeOfWeightTurnaroundString processName; //process numberQueue next;public Queue(int arrTime, int serviceTime, String processName) {this.arrTime = arrTime;this.serviceTime = serviceTime;this.processName = processName;}public Queue() {} }/*** Simulate FCFS algorithm class*/ class SimulateFCFS {private Queue head = new Queue(-1, -1, null);private int timer = 0;private Queue tail = head;public void createQueue() {Queue arr = null;Queue temp = head;Scanner scanner = new Scanner(System.in);System.out.printf("Please enter the number of process tasks to initialize the simulation:");int n = scanner.nextInt();for (int i = 1; i <= n; i++) {System.out.printf("Please enter the process number, start time, and service time of the %d process:",i);arr = new Queue();keyBordInput(arr, scanner);calTime(arr);temp.next = arr;temp = arr;}this.tail = arr;System.out.println("Simulation allocation is successful!");}/*** Completion time of calculation process - Turnaround time - Weighted turnaround time* @param arr*/public void calTime(Queue arr) {Queue temp = arr;if (this.timer < temp.arrTime) {this.timer = arr.arrTime;} else {if (timer == 0) {this.timer = temp.arrTime;}}temp.finishTime = temp.serviceTime + this.timer;temp.turnTime = temp.finishTime - temp.arrTime;temp.weightTurnTime = (temp.turnTime * 1.0) / (temp.serviceTime * 1.0);this.timer += temp.serviceTime;}/*** Process number，arrival time，service time entered from the keyboard* @param arr* @param scanner*/public void keyBordInput(Queue arr, Scanner scanner) {arr.processName = scanner.next();arr.arrTime = scanner.nextInt();arr.serviceTime = scanner.nextInt();}/*** Assign a process to the queue*/public void assignProcess() {Queue newProcess = new Queue();Scanner scanner = new Scanner(System.in);System.out.printf("Please enter the add process number,start time,and service time of the process:");keyBordInput(newProcess, scanner);calTime(newProcess);this.tail.next = newProcess;this.tail = newProcess;}/*** Complish a task of process from the queue*/ // public void finishProcessTask() { // Queue workingProcess = head; // // }/*** Complish all task of process from the queue*/public void finishAllProcessTask() {if (isEmpty()) {return;}Queue cur = head.next;System.out.println("Process number========Arrive time======Service time=======finish Time=======Turn time======WeightTurn time");while (true) {System.out.printf("\t\t%s\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t%d\t\t\t\t%f",cur.processName,cur.arrTime,cur.serviceTime,cur.finishTime,cur.turnTime,cur.weightTurnTime);System.out.println();if (cur.next == null) {break;}cur = cur.next;}}public boolean isEmpty() {if (head.next == null) {System.out.println("Queue is null!");return true;}return false;} }

三、代碼分析

1.使用節(jié)點(diǎn)模擬進(jìn)程

因?yàn)樾枰?jì)算完成時(shí)間、周轉(zhuǎn)時(shí)間、帶權(quán)周轉(zhuǎn)時(shí)間，所以需要事先給出每個(gè)進(jìn)程到達(dá)時(shí)間和服務(wù)時(shí)間

模擬時(shí)至少需要以下幾個(gè)屬性（Queue類(lèi)對(duì)象模擬進(jìn)程）

class Queue {int arrTime; //timeOfArrivalint serviceTime; //timeOfServiceint finishTime; //timeOfComplishint turnTime; //timeOfTurnarounddouble weightTurnTime; //timeOfWeightTurnaroundString processName; //process numberQueue next;public Queue(int arrTime, int serviceTime, String processName) {this.arrTime = arrTime;this.serviceTime = serviceTime;this.processName = processName;}public Queue() {} }

2.SimulateFCFS（核心模擬FCFS類(lèi)）

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以下分析核心模擬類(lèi)

3.創(chuàng)建一個(gè)節(jié)點(diǎn)為n的隊(duì)列（模擬就緒隊(duì)列）

public void createQueue() {Queue arr = null;Queue temp = head; Scanner scanner = new Scanner(System.in);System.out.printf("Please enter the number of process tasks to initialize the simulation:");int n = scanner.nextInt(); //創(chuàng)建節(jié)點(diǎn)數(shù)為n的隊(duì)列for (int i = 1; i <= n; i++) {System.out.printf("Please enter the process number, start time, and service time of the %d process:",i);arr = new Queue();keyBordInput(arr, scanner);//這個(gè)自定義的函數(shù)主要用來(lái)輸入進(jìn)程的到達(dá)時(shí)間和服務(wù)時(shí)間calTime(arr); //該自定義函數(shù)用來(lái)計(jì)算完成時(shí)間、周轉(zhuǎn)時(shí)間、帶權(quán)周轉(zhuǎn)時(shí)間temp.next = arr;temp = arr; //進(jìn)行節(jié)點(diǎn)連接}this.tail = arr;System.out.println("Simulation allocation is successful!");}

4.核心計(jì)算分析

(如果是第一個(gè)進(jìn)程） 完成時(shí)間 = 服務(wù)時(shí)間 + 到達(dá)時(shí)間


如果是n>1的進(jìn)程就要考慮前面進(jìn)程所花費(fèi)的時(shí)間和該進(jìn)程到達(dá)時(shí)間的長(zhǎng)短問(wèn)題。如果前面所花費(fèi)的完成時(shí)間大于該進(jìn)程的到達(dá)進(jìn)程，則（完成時(shí)間 = 服務(wù)時(shí)間+上一個(gè)進(jìn)程的完成時(shí)間）
反之則是 （完成時(shí)間= 服務(wù)時(shí)間+到達(dá)時(shí)間）

//timer是全局變量，用來(lái)計(jì)算完成時(shí)間（解決上面的問(wèn)題） public void calTime(Queue arr) {Queue temp = arr;if (this.timer < temp.arrTime) {this.timer = arr.arrTime;} else {if (timer == 0) {this.timer = temp.arrTime;}}temp.finishTime = temp.serviceTime + this.timer;temp.turnTime = temp.finishTime - temp.arrTime;temp.weightTurnTime = (temp.turnTime * 1.0) / (temp.serviceTime * 1.0);this.timer += temp.serviceTime;}

5.輸入到達(dá)時(shí)間和服務(wù)時(shí)間（模擬進(jìn)程到達(dá)和服務(wù))

public void keyBordInput(Queue arr, Scanner scanner) {arr.processName = scanner.next();arr.arrTime = scanner.nextInt();arr.serviceTime = scanner.nextInt();}

6.出隊(duì)列（模擬完成所有進(jìn)程工作）

public void finishAllProcessTask() {if (isEmpty()) {return;}Queue cur = head.next;System.out.println("Process number========Arrive time======Service time=======finish Time=======Turn time======WeightTurn time");while (true) {System.out.printf("\t\t%s\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t\t%d\t\t\t\t%d\t\t\t\t%f",cur.processName,cur.arrTime,cur.serviceTime,cur.finishTime,cur.turnTime,cur.weightTurnTime);System.out.println();if (cur.next == null) {break;}cur = cur.next;}}

總結(jié)

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