循環調度的C程序

我們給定了n個進程及其對應的突發時間和時間量，任務是找到平均等待時間和平均週轉時間並顯示結果。

#什麼是循環調度？

輪循是一種專為分時系統設計的CPU調度演算法。它更像是 FCFS 調度演算法，但有一個變化是循環進程受量子時間大小的限制。一個小的時間單位被稱為時間量子或時間片。時間量的範圍可以是 10 到 100 毫秒。 CPU將就緒佇列視為循環佇列，以給定的時間片執行程序。它遵循搶佔式方法，因為固定時間被分配給進程。它唯一的缺點是上下文切換的開銷。

#我們需要計算什麼？

Completion Time#是行程所需的時間完成其執行

##週轉時間#是流程提交和完成之間的時間間隔。

週轉時間= 流程完成– 流程提交

等待時間是週轉時間和突發時間之間的差

等待時間= 週轉時間- 突發時間

範例

我們有3 個進程P1、P2 和P3 對應的突發時間為24、3 及3

Process#Burst TimeP124P2#3##P3##3#由於時間量為4 毫秒，進程P1 獲得前4 毫秒，但還需要20 毫秒才能完成執行，但CPU 會在第一個時間片後搶佔它， CPU將被指派給下一個行程P2。如表中所示，進程 P2 只需 3 毫秒即可完成其執行，因此 CPU 將僅分配 3 毫秒的時間量，而不是 4 毫秒。

使用甘特圖，平均等待時間計算如下-

平均等待時間= 17/3 = 5.66 毫秒

演算法

Start
Step 1-> In function int turnarroundtime(int processes[], int n, int bt[], int wt[], int tat[])
   Loop For i = 0 and i < n and i++
      Set tat[i] = bt[i] + wt[i]
   return 1
Step 2-> In function int waitingtime(int processes[], int n, int bt[], int wt[], int quantum)
Declare rem_bt[n]
   Loop For i = 0 and i < n and i++
      Set rem_bt[i] = bt[i]
      Set t = 0
   Loop While (1)
      Set done = true
   Loop For i = 0 and i < n and i++
      If rem_bt[i] > 0 then,
         Set done = false
      If rem_bt[i] > quantum then,
         Set t = t + quantum
         Set rem_bt[i] = rem_bt[i] - quantum
      Else
         Set t = t + rem_bt[i]
         Set wt[i] = t - bt[i]
         Set rem_bt[i] = 0
      If done == true then,
   Break
Step 3->In function int findavgTime(int processes[], int n, int bt[], int quantum)
   Declare and initialize wt[n], tat[n], total_wt = 0, total_tat = 0
   Call function waitingtime(processes, n, bt, wt, quantum)
   Call function turnarroundtime(processes, n, bt, wt, tat)
   Print "Processes Burst Time Waiting Time turnaround time "
   Loop For i=0 and i<n and i++
   Set total_wt = total_wt + wt[i]
   Set total_tat = total_tat + tat[i]
   Print the value i+1, bt[i], wt[i], tat[i]
   Print "Average waiting time = total_wt / n
   Print "Average turnaround time =total_tat / n
Step 4-> In function int main()
   Delcare and initialize processes[] = { 1, 2, 3}
   Declare and initialize n = sizeof processes / sizeof processes[0]
   Declare and initialize burst_time[] = {8, 6, 12}
   Set quantum = 2
   Call function findavgTime(processes, n, burst_time, quantum)

範例

實例示範

#include <stdio.h>
// Function to calculate turn around time
int turnarroundtime(int processes[], int n,
int bt[], int wt[], int tat[]) {
   // calculating turnaround time by adding
   // bt[i] + wt[i]
   for (int i = 0; i < n ; i++)
   tat[i] = bt[i] + wt[i];
   return 1;
}
// Function to find the waiting time for all
// processes
int waitingtime(int processes[], int n,
int bt[], int wt[], int quantum) {
   // Make a copy of burst times bt[] to store remaining
   // burst times.
   int rem_bt[n];
   for (int i = 0 ; i < n ; i++)
   rem_bt[i] = bt[i];
   int t = 0; // Current time
   // Keep traversing processes in round robin manner
   // until all of them are not done.
   while (1) {
      bool done = true;
      // Traverse all processes one by one repeatedly
      for (int i = 0 ; i < n; i++) {
         // If burst time of a process is greater than 0
         // then only need to process further
         if (rem_bt[i] > 0) {
            done = false; // There is a pending process
            if (rem_bt[i] > quantum) {
               // Increase the value of t i.e. shows
               // how much time a process has been processed
               t += quantum;
               // Decrease the burst_time of current process
               // by quantum
               rem_bt[i] -= quantum;
            }
            // If burst time is smaller than or equal to
            // quantum. Last cycle for this process
            else {
               // Increase the value of t i.e. shows
               // how much time a process has been processed
               t = t + rem_bt[i];
               // Waiting time is current time minus time
               // used by this process
               wt[i] = t - bt[i];
               // As the process gets fully executed
               // make its remaining burst time = 0
               rem_bt[i] = 0;
            }
         }
      }
      // If all processes are done
      if (done == true)
         break;
   }
   return 1;
}
// Function to calculate average time
int findavgTime(int processes[], int n, int bt[],
int quantum) {
   int wt[n], tat[n], total_wt = 0, total_tat = 0;
   // Function to find waiting time of all processes
   waitingtime(processes, n, bt, wt, quantum);
   // Function to find turn around time for all processes
   turnarroundtime(processes, n, bt, wt, tat);
   // Display processes along with all details
   printf("Processes Burst Time Waiting Time turnaround time</p><p>");
   // Calculate total waiting time and total turn
   // around time
   for (int i=0; i<n; i++) {
      total_wt = total_wt + wt[i];
      total_tat = total_tat + tat[i];
      printf("\t%d\t\t\t%d\t\t\t%d\t\t\t%d</p><p>",i+1, bt[i], wt[i], tat[i]);
   }
   printf("Average waiting time = %f", (float)total_wt / (float)n);
   printf("</p><p>Average turnaround time = %f</p><p>", (float)total_tat / (float)n);
   return 1;
}
// main function
int main() {
   // process id&#39;s
   int processes[] = { 1, 2, 3};
   int n = sizeof processes / sizeof processes[0];
   // Burst time of all processes
   int burst_time[] = {8, 6, 12};
   // Time quantum
   int quantum = 2;
   findavgTime(processes, n, burst_time, quantum);
   return 0;
}

輸出

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