引言
进程调度是操作系统中的核心模块，它决定了进程在处理器上的执行顺序和时间，从而影响了系统的性能和用户的体验。本文将深入浅出地解析操作系统中的进程调度算法，并通过C语言实战展示如何实现这些算法。
一、进程调度算法概述
1.1 基本概念
进程调度算法是指在进程等待执行时，根据一定的原则和策略，从就绪队列中选择一个或多个进程来占用处理器。常见的进程调度算法包括：
- 先来先服务（FCFS）
- 短作业优先（SJF）
- 时间片轮转（RR）
- 最高优先数（HPF）
- 多级反馈队列（MFQ）
1.2 算法选择
选择合适的进程调度算法需要考虑以下因素：
- 系统的响应时间
- 系统的吞吐量
- 系统的公平性
- 系统的实时性
二、C语言实战解析
以下将展示如何使用C语言实现几种常见的进程调度算法。
2.1 先来先服务（FCFS）
#include <stdio.h>
#define MAXPROC 5
typedef struct {
int id;
int arrive;
int burst;
} Process;
int main() {
Process proc[MAXPROC] = {{1, 0, 3}, {2, 1, 6}, {3, 2, 4}, {4, 3, 5}, {5, 4, 2}};
int waitingTime[MAXPROC];
int turnaroundTime[MAXPROC];
int completionTime[MAXPROC];
int currentTime = 0;
int i, j;
// 初始化等待时间和完成时间
for (i = 0; i < MAXPROC; i++) {
waitingTime[i] = 0;
turnaroundTime[i] = 0;
completionTime[i] = 0;
}
// FCFS调度
for (i = 0; i < MAXPROC; i++) {
for (j = 0; j < i; j++) {
if (proc[j].arrive < proc[i].arrive) {
currentTime += proc[j].burst;
}
}
waitingTime[i] = currentTime - proc[i].arrive;
turnaroundTime[i] = waitingTime[i] + proc[i].burst;
currentTime += proc[i].burst;
completionTime[i] = currentTime;
}
// 输出结果
printf("Process ID\tArrival Time\tBurst Time\tWaiting Time\tTurnaround Time\tCompletion Time\n");
for (i = 0; i < MAXPROC; i++) {
printf("%d\t\t%d\t\t%d\t\t%d\t\t\t%d\t\t\t%d\n", proc[i].id, proc[i].arrive, proc[i].burst, waitingTime[i], turnaroundTime[i], completionTime[i]);
}
return 0;
}
2.2 短作业优先（SJF）
#include <stdio.h>
#define MAXPROC 5
typedef struct {
int id;
int arrive;
int burst;
} Process;
int main() {
Process proc[MAXPROC] = {{1, 0, 3}, {2, 1, 6}, {3, 2, 4}, {4, 3, 5}, {5, 4, 2}};
int waitingTime[MAXPROC];
int turnaroundTime[MAXPROC];
int completionTime[MAXPROC];
int i, j;
// 初始化等待时间和完成时间
for (i = 0; i < MAXPROC; i++) {
waitingTime[i] = 0;
turnaroundTime[i] = 0;
completionTime[i] = 0;
}
// SJF调度
for (i = 0; i < MAXPROC; i++) {
int minIndex = i;
for (j = i + 1; j < MAXPROC; j++) {
if (proc[j].arrive <= currentTime && proc[j].burst < proc[minIndex].burst) {
minIndex = j;
}
}
waitingTime[i] = currentTime - proc[minIndex].arrive;
turnaroundTime[i] = waitingTime[i] + proc[minIndex].burst;
currentTime += proc[minIndex].burst;
completionTime[i] = currentTime;
proc[minIndex].arrive = currentTime;
proc[minIndex].burst = 0;
}
// 输出结果
printf("Process ID\tArrival Time\tBurst Time\tWaiting Time\tTurnaround Time\tCompletion Time\n");
for (i = 0; i < MAXPROC; i++) {
printf("%d\t\t%d\t\t%d\t\t%d\t\t\t%d\t\t\t%d\n", proc[i].id, proc[i].arrive, proc[i].burst, waitingTime[i], turnaroundTime[i], completionTime[i]);
}
return 0;
}
2.3 时间片轮转（RR）
#include <stdio.h>
#define MAXPROC 5
#define QUANTUM 2
typedef struct {
int id;
int arrive;
int burst;
} Process;
int main() {
Process proc[MAXPROC] = {{1, 0, 7}, {2, 1, 5}, {3, 2, 3}, {4, 3, 9}, {5, 4, 6}};
int waitingTime[MAXPROC];
int turnaroundTime[MAXPROC];
int completionTime[MAXPROC];
int i, j;
// 初始化等待时间和完成时间
for (i = 0; i < MAXPROC; i++) {
waitingTime[i] = 0;
turnaroundTime[i] = 0;
completionTime[i] = 0;
}
// RR调度
for (i = 0; i < MAXPROC; i++) {
if (proc[i].burst > QUANTUM) {
waitingTime[i] = currentTime - proc[i].arrive;
turnaroundTime[i] = waitingTime[i] + proc[i].burst;
currentTime += proc[i].burst - QUANTUM;
proc[i].burst = 0;
} else {
waitingTime[i] = currentTime - proc[i].arrive;
turnaroundTime[i] = waitingTime[i] + proc[i].burst;
currentTime += proc[i].burst;
proc[i].burst = 0;
}
completionTime[i] = currentTime;
}
// 输出结果
printf("Process ID\tArrival Time\tBurst Time\tWaiting Time\tTurnaround Time\tCompletion Time\n");
for (i = 0; i < MAXPROC; i++) {
printf("%d\t\t%d\t\t%d\t\t%d\t\t\t%d\t\t\t%d\n", proc[i].id, proc[i].arrive, proc[i].burst, waitingTime[i], turnaroundTime[i], completionTime[i]);
}
return 0;
}
2.4 最高优先数（HPF）
#include <stdio.h>
#define MAXPROC 5
typedef struct {
int id;
int arrive;
int burst;
int priority;
} Process;
int main() {
Process proc[MAXPROC] = {{1, 0, 3, 5}, {2, 1, 6, 2}, {3, 2, 4, 1}, {4, 3, 5, 3}, {5, 4, 2, 4}};
int waitingTime[MAXPROC];
int turnaroundTime[MAXPROC];
int completionTime[MAXPROC];
int i, j;
// 初始化等待时间和完成时间
for (i = 0; i < MAXPROC; i++) {
waitingTime[i] = 0;
turnaroundTime[i] = 0;
completionTime[i] = 0;
}
// HPF调度
for (i = 0; i < MAXPROC; i++) {
int maxIndex = i;
for (j = i + 1; j < MAXPROC; j++) {
if (proc[j].priority > proc[maxIndex].priority && proc[j].arrive <= currentTime) {
maxIndex = j;
}
}
waitingTime[i] = currentTime - proc[maxIndex].arrive;
turnaroundTime[i] = waitingTime[i] + proc[maxIndex].burst;
currentTime += proc[maxIndex].burst;
completionTime[i] = currentTime;
proc[maxIndex].arrive = currentTime;
proc[maxIndex].burst = 0;
}
// 输出结果
printf("Process ID\tArrival Time\tBurst Time\tPriority\tWaiting Time\tTurnaround Time\tCompletion Time\n");
for (i = 0; i < MAXPROC; i++) {
printf("%d\t\t%d\t\t%d\t\t%d\t\t\t%d\t\t\t%d\t\t\t%d\n", proc[i].id, proc[i].arrive, proc[i].burst, proc[i].priority, waitingTime[i], turnaroundTime[i], completionTime[i]);
}
return 0;
}
2.5 多级反馈队列（MFQ）
#include <stdio.h>
#define MAXPROC 5
#define MAXLEVEL 3
typedef struct {
int id;
int arrive;
int burst;
int priority;
} Process;
int main() {
Process proc[MAXPROC] = {{1, 0, 7, 5}, {2, 1, 5, 2}, {3, 2, 3, 1}, {4, 3, 9, 3}, {5, 4, 6, 4}};
int waitingTime[MAXPROC];
int turnaroundTime[MAXPROC];
int completionTime[MAXPROC];
int i, j;
// 初始化等待时间和完成时间
for (i = 0; i < MAXPROC; i++) {
waitingTime[i] = 0;
turnaroundTime[i] = 0;
completionTime[i] = 0;
}
// MFQ调度
for (i = 0; i < MAXPROC; i++) {
int level = 0;
while (level < MAXLEVEL) {
int index = -1;
int timeSlice = 1 << level; // 时间片
for (j = 0; j < MAXPROC; j++) {
if (proc[j].priority == level && proc[j].arrive <= currentTime) {
index = j;
break;
}
}
if (index == -1) {
level++;
continue;
}
if (proc[index].burst > timeSlice) {
waitingTime[i] = currentTime - proc[index].arrive;
turnaroundTime[i] = waitingTime[i] + proc[index].burst;
currentTime += timeSlice;
proc[index].burst -= timeSlice;
if (proc[index].burst <= timeSlice) {
level++;
}
} else {
waitingTime[i] = currentTime - proc[index].arrive;
turnaroundTime[i] = waitingTime[i] + proc[index].burst;
currentTime += proc[index].burst;
proc[index].burst = 0;
}
completionTime[i] = currentTime;
proc[index].priority++;
}
}
// 输出结果
printf("Process ID\tArrival Time\tBurst Time\tPriority\tWaiting Time\tTurnaround Time\tCompletion Time\n");
for (i = 0; i < MAXPROC; i++) {
printf("%d\t\t%d\t\t%d\t\t%d\t\t\t%d\t\t\t%d\t\t\t%d\n", proc[i].id, proc[i].arrive, proc[i].burst, proc[i].priority, waitingTime[i], turnaroundTime[i], completionTime[i]);
}
return 0;
}
三、总结
本文深入浅出地解析了操作系统中的进程调度算法，并通过C语言实战展示了如何实现这些算法。通过对不同算法的比较和分析，我们可以更好地理解各种算法的优缺点，为实际应用选择合适的调度策略。