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法學C語言FCFS排程程式
假設我們有n個程序，即P1、P2、P3、……、Pn及其對應的突發時間。任務是使用先來先服務(FCFS) CPU排程演算法找到平均等待時間和平均週轉時間。
什麼是等待時間和週轉時間？
週轉時間是程序提交和完成之間的時間間隔。
週轉時間 = 程序完成時間 – 程序提交時間
等待時間是週轉時間和突發時間之差
等待時間 = 週轉時間 – 突發時間
什麼是FCFS排程？
先來先服務(FCFS)，也稱為先進先出(FIFO)，是一種CPU排程演算法，其中CPU按照程序在就緒佇列中排隊的順序分配給程序。
FCFS遵循非搶佔式排程，這意味著一旦CPU分配給一個程序，它就不會離開CPU，直到程序終止或由於某些I/O中斷而暫停。
示例
假設有四個程序按照P2、P3、P1的順序到達，它們對應的執行時間如下表所示。此外，假設它們的到達時間為0。
| 程序 | 到達順序 | 執行時間（毫秒） |
|---|---|---|
| P1 | 3 | 15 |
| P2 | 1 | 3 |
| P3 | 2 | 3 |
甘特圖顯示系統中程序P1、P2和P3的等待時間
如上所示：
程序P2的等待時間為0
程序P3的等待時間為3
程序P1的等待時間為6
平均時間 = (0 + 3 + 6) / 3 = 3 毫秒。
由於我們假設到達時間為0，因此週轉時間和完成時間相同。
示例
Input-: processes = P1, P2, P3 Burst time = 5, 8, 12 Output-: Processes Burst Waiting Turn around 1 5 0 5 2 8 5 13 3 12 13 25 Average Waiting time = 6.000000 Average turn around time = 14.333333
演算法
Start Step 1-> In function int waitingtime(int proc[], int n, int burst_time[], int wait_time[])
Set wait_time[0] = 0
Loop For i = 1 and i < n and i++
Set wait_time[i] = burst_time[i-1] + wait_time[i-1]
End For
Step 2-> In function int turnaroundtime( int proc[], int n, int burst_time[], int wait_time[], int tat[])
Loop For i = 0 and i < n and i++
Set tat[i] = burst_time[i] + wait_time[i]
End For
Step 3-> In function int avgtime( int proc[], int n, int burst_time[])
Declare and initialize wait_time[n], tat[n], total_wt = 0, total_tat = 0;
Call waitingtime(proc, n, burst_time, wait_time)
Call turnaroundtime(proc, n, burst_time, wait_time, tat)
Loop For i=0 and i<n and i++
Set total_wt = total_wt + wait_time[i]
Set total_tat = total_tat + tat[i]
Print process number, burstime wait time and turnaround time
End For
Print "Average waiting time =i.e. total_wt / n
Print "Average turn around time = i.e. total_tat / n
Step 4-> In int main()
Declare the input int proc[] = { 1, 2, 3}
Declare and initialize n = sizeof proc / sizeof proc[0]
Declare and initialize burst_time[] = {10, 5, 8}
Call avgtime(proc, n, burst_time)
Stop示例
#include <stdio.h> // Function to find the waiting time for all processes int waitingtime(int proc[], int n, int burst_time[], int wait_time[]) { // waiting time for first process is 0 wait_time[0] = 0; // calculating waiting time for (int i = 1; i < n ; i++ ) wait_time[i] = burst_time[i-1] + wait_time[i-1] ; return 0; } // Function to calculate turn around time int turnaroundtime( int proc[], int n, int burst_time[], int wait_time[], int tat[]) { // calculating turnaround time by adding // burst_time[i] + wait_time[i] int i; for ( i = 0; i < n ; i++) tat[i] = burst_time[i] + wait_time[i]; return 0; } //Function to calculate average time int avgtime( int proc[], int n, int burst_time[]) { int wait_time[n], tat[n], total_wt = 0, total_tat = 0; int i; //Function to find waiting time of all processes waitingtime(proc, n, burst_time, wait_time); //Function to find turn around time for all processes turnaroundtime(proc, n, burst_time, wait_time, tat); //Display processes along with all details printf("Processes Burst Waiting Turn around
"); // Calculate total waiting time and total turn // around time for ( i=0; i<n; i++) { total_wt = total_wt + wait_time[i]; total_tat = total_tat + tat[i]; printf(" %d\t %d\t\t %d \t%d
", i+1, burst_time[i], wait_time[i], tat[i]); } printf("Average waiting time = %f
", (float)total_wt / (float)n); printf("Average turn around time = %f
", (float)total_tat / (float)n); return 0; } // main function int main() { //process id's int proc[] = { 1, 2, 3}; int n = sizeof proc / sizeof proc[0]; //Burst time of all processes int burst_time[] = {5, 8, 12}; avgtime(proc, n, burst_time); return 0; }
輸出
Processes Burst Waiting Turn around 1 5 0 5 2 8 5 13 3 12 13 25 Average Waiting time = 6.000000 Average turn around time = 14.333333
更新於：2023年9月2日
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