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法律研究C++优先级调度程序
我们给定n个进程，即P1、P2、P3、……、Pn，以及每个进程对应的突发时间和优先级。任务是使用优先级CPU调度算法找到平均等待时间、平均周转时间和进程执行顺序。
什么是等待时间和周转时间？
周转时间是从提交一个进程到完成该进程的时间间隔。
周转时间 = 进程完成时间 – 进程提交时间
等待时间是周转时间和突发时间之间的差值
等待时间 = 周转时间 – 突发时间
什么是优先级调度？
在优先级调度中，每个进程都与一个优先级相关联，范围从0到10，其中整数0表示最低优先级，10表示最高优先级。优先级可以通过两种方式定义，即内部和外部。此外，优先级调度可以是抢占式的或非抢占式的。
在抢占式优先级调度中，如果新到达进程的优先级高于正在执行的进程的优先级，则调度程序将抢占CPU。
在非抢占式优先级调度中，调度程序将新进程排队到就绪队列的头部。
使用优先级调度算法的缺点是不确定阻塞或饥饿。将会有一个低优先级进程可能不得不无限期地等待资源，因为高优先级进程会导致饥饿问题。
示例
假设有4个进程P1、P2、P3和P4，以及每个进程对应的突发时间和优先级，其中0表示最低优先级，10表示最高优先级。
| 进程 | 突发时间 | 优先级 |
|---|---|---|
| P1 | 15 | 2 |
| P2 | 13 | 0 |
| P3 | 10 | 4 |
| P4 | 11 | 1 |
执行多个进程的顺序将使用下面给出的甘特图表示
算法
Start
Step 1-> Make a structure Process with variables pid, bt, priority
Step 2-> In function bool compare(Process a, Process b)
Return (a.priority > b.priority)
Step 3-> In function waitingtime(Process pro[], int n, int wt[])
Set wt[0] = 0
Loop For i = 1 and i < n and i++
Set wt[i] = pro[i-1].bt + wt[i-1]
End
Step 4-> In function turnarround( Process pro[], int n, int wt[], int tat[])
Loop For i = 0 and i < n and i++
Set tat[i] = pro[i].bt + wt[i]
End Loop
Step 5-> In function avgtime(Process pro[], int n)
Declare and initialize wt[n], tat[n], total_wt = 0, total_tat = 0
Call function waitingtime(pro, n, wt)
Call function turnarround(pro, n, wt, tat)
Print “Processes, Burst time, Waiting time, Turn around time"
Loop For i=0 and i<n and i++
Set total_wt = total_wt + wt[i]
total_tat = total_tat + tat[i]
End Loop
Print values of “Processes, Burst time, Waiting time, Turn around time"
Print Average waiting time, Average turn around time
Step 6-> In function scheduling(Process pro[], int n)
Call function sort(pro, pro + n, compare)
Loop For i = 0 and i < n and i++
Print the order.
End Loop
Call function avgtime(pro, n)
Step 7-> In function int main()
Declare and initialize Process pro[] = {{1, 10, 2}, {2, 5, 0}, {3, 8, 1}}
Declare and initialize n = sizeof pro / sizeof pro[0]
Call function scheduling(pro, n)
Stop示例
#include<bits/stdc++.h>
using namespace std;
struct Process {
int pid; // Process ID
int bt; // CPU Burst time required
int priority; // Priority of this process
};
// sorting the Process acc. to the priority
bool compare(Process a, Process b) {
return (a.priority > b.priority);
}
void waitingtime(Process pro[], int n, int wt[]) {
// Initial waiting time for a process is 0
wt[0] = 0;
// calculating waiting time
for (int i = 1; i < n ; i++ )
wt[i] = pro[i-1].bt + wt[i-1] ;
}
// Function to calculate turn around time
void turnarround( Process pro[], int n, int wt[], int tat[]) {
// calculating turnaround time by adding
// bt[i] + wt[i]
for (int i = 0; i < n ; i++)
tat[i] = pro[i].bt + wt[i];
}
//Function to calculate average time
void avgtime(Process pro[], int n) {
int wt[n], tat[n], total_wt = 0, total_tat = 0;
//Function to find waiting time of all processes
waitingtime(pro, n, wt);
//Function to find turn around time for all processes
turnarround(pro, n, wt, tat);
//Display processes along with all details
cout << "\nProcesses "<< " Burst time " << " Waiting time " << " Turn around time\n";
// 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];
cout << " " << pro[i].pid << "\t\t" << pro[i].bt << "\t " << wt[i] << "\t\t " << tat[i] <<endl;
}
cout << "\nAverage waiting time = " << (float)total_wt / (float)n;
cout << "\nAverage turn around time = " << (float)total_tat / (float)n;
}
void scheduling(Process pro[], int n) {
// Sort processes by priority
sort(pro, pro + n, compare);
cout<< "Order in which processes gets executed \n";
for (int i = 0 ; i < n; i++)
cout << pro[i].pid <<" " ;
avgtime(pro, n);
}
// main function
int main() {
Process pro[] = {{1, 10, 2}, {2, 5, 0}, {3, 8, 1}};
int n = sizeof pro / sizeof pro[0];
scheduling(pro, n);
return 0;
}输出
Order in which processes gets executed 1 3 2 Processes Burst time Waiting time Turn around time 1 10 0 10 3 8 10 18 2 5 18 23 Average waiting time = 9.33333 Average turn around time = 17
更新于: 2019年12月20日
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