FCFS CPU 调度程序|设置 1
给定 n 个进程及其突发时间，任务是使用 FCFS 调度算法找到平均等待时间和平均周转时间。
先进先出（FIFO），也称为先来先服务（FCFS），是最简单的调度算法。 FIFO 只是按照进程到达就绪队列的顺序对进程进行排队。
在这种情况下，首先执行的进程将首先执行，并且只有在前一个进程完全执行后才开始下一个进程。
这里我们考虑所有进程的到达时间都是 0。
如何使用程序在循环中计算以下时间？
- 完成时间：进程完成执行的时间。
- 周转时间：完成时间和到达时间之间的时间差。周转时间 = 完成时间 - 到达时间
- 等待时间（WT）：周转时间和突发时间之间的时间差。
等待时间 = 周转时间 - 爆发时间
在这篇文章中，我们假设到达时间为 0，所以转身和完成时间是相同的。
执行：
1- Input the processes along with their burst time (bt).
2- Find waiting time (wt) for all processes.
3- As first process that comes need not to wait so
waiting time for process 1 will be 0 i.e. wt[0] = 0.
4- Find waiting time for all other processes i.e. for
process i ->
wt[i] = bt[i-1] + wt[i-1] .
5- Find turnaround time = waiting_time + burst_time
for all processes.
6- Find average waiting time =
total_waiting_time / no_of_processes.
7- Similarly, find average turnaround time =
total_turn_around_time / no_of_processes.C++
// C++ program for implementation of FCFS
// scheduling
#include
using namespace std;
// Function to find the waiting time for all
// processes
void findWaitingTime(int processes[], int n,
int bt[], int wt[])
{
// waiting time for first process is 0
wt[0] = 0;
// calculating waiting time
for (int i = 1; i < n ; i++ )
wt[i] = bt[i-1] + wt[i-1] ;
}
// Function to calculate turn around time
void findTurnAroundTime( 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];
}
//Function to calculate average time
void findavgTime( int processes[], int n, int bt[])
{
int wt[n], tat[n], total_wt = 0, total_tat = 0;
//Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt);
//Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
//Display processes along with all details
cout << "Processes "<< " Burst time "
<< " Waiting time " << " Turn around time\n";
// Calculate total waiting time and total turn
// around time
for (int i=0; iC// C program for implementation of FCFS
// scheduling
#include
// Function to find the waiting time for all
// processes
void findWaitingTime(int processes[], int n,
int bt[], int wt[])
{
// waiting time for first process is 0
wt[0] = 0;
// calculating waiting time
for (int i = 1; i < n ; i++ )
wt[i] = bt[i-1] + wt[i-1] ;
}
// Function to calculate turn around time
void findTurnAroundTime( 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];
}
//Function to calculate average time
void findavgTime( int processes[], int n, int bt[])
{
int wt[n], tat[n], total_wt = 0, total_tat = 0;
//Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt);
//Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
//Display processes along with all details
printf("Processes Burst time Waiting time Turn around time\n");
// Calculate total waiting time and total turn
// around time
for (int i=0; i
Java
// Java program for implementation of FCFS
// scheduling
import java.text.ParseException;
class GFG {
// Function to find the waiting time for all
// processes
static void findWaitingTime(int processes[], int n,
int bt[], int wt[]) {
// waiting time for first process is 0
wt[0] = 0;
// calculating waiting time
for (int i = 1; i < n; i++) {
wt[i] = bt[i - 1] + wt[i - 1];
}
}
// Function to calculate turn around time
static void findTurnAroundTime(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];
}
}
//Function to calculate average time
static void findavgTime(int processes[], int n, int bt[]) {
int wt[] = new int[n], tat[] = new int[n];
int total_wt = 0, total_tat = 0;
//Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt);
//Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
//Display processes along with all details
System.out.printf("Processes 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];
System.out.printf(" %d ", (i + 1));
System.out.printf(" %d ", bt[i]);
System.out.printf(" %d", wt[i]);
System.out.printf(" %d\n", tat[i]);
}
float s = (float)total_wt /(float) n;
int t = total_tat / n;
System.out.printf("Average waiting time = %f", s);
System.out.printf("\n");
System.out.printf("Average turn around time = %d ", t);
}
// Driver code
public static void main(String[] args) throws ParseException {
//process id's
int processes[] = {1, 2, 3};
int n = processes.length;
//Burst time of all processes
int burst_time[] = {10, 5, 8};
findavgTime(processes, n, burst_time);
}
}
// This code is contributed by 29ajaykumar
Python 3
# Python3 program for implementation
# of FCFS scheduling
# Function to find the waiting
# time for all processes
def findWaitingTime(processes, n,
bt, wt):
# waiting time for
# first process is 0
wt[0] = 0
# calculating waiting time
for i in range(1, n ):
wt[i] = bt[i - 1] + wt[i - 1]
# Function to calculate turn
# around time
def findTurnAroundTime(processes, n,
bt, wt, tat):
# calculating turnaround
# time by adding bt[i] + wt[i]
for i in range(n):
tat[i] = bt[i] + wt[i]
# Function to calculate
# average time
def findavgTime( processes, n, bt):
wt = [0] * n
tat = [0] * n
total_wt = 0
total_tat = 0
# Function to find waiting
# time of all processes
findWaitingTime(processes, n, bt, wt)
# Function to find turn around
# time for all processes
findTurnAroundTime(processes, n,
bt, wt, tat)
# Display processes along
# with all details
print( "Processes Burst time " +
" Waiting time " +
" Turn around time")
# Calculate total waiting time
# and total turn around time
for i in range(n):
total_wt = total_wt + wt[i]
total_tat = total_tat + tat[i]
print(" " + str(i + 1) + "\t\t" +
str(bt[i]) + "\t " +
str(wt[i]) + "\t\t " +
str(tat[i]))
print( "Average waiting time = "+
str(total_wt / n))
print("Average turn around time = "+
str(total_tat / n))
# Driver code
if __name__ =="__main__":
# process id's
processes = [ 1, 2, 3]
n = len(processes)
# Burst time of all processes
burst_time = [10, 5, 8]
findavgTime(processes, n, burst_time)
# This code is contributed
# by ChitraNayal
C#
// C# program for implementation of FCFS
// scheduling
using System;
class GFG
{
// Function to find the waiting time for all
// processes
static void findWaitingTime(int []processes, int n,
int []bt, int[] wt)
{
// waiting time for first process is 0
wt[0] = 0;
// calculating waiting time
for (int i = 1; i < n; i++)
{
wt[i] = bt[i - 1] + wt[i - 1];
}
}
// Function to calculate turn around time
static void findTurnAroundTime(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];
}
}
// Function to calculate average time
static void findavgTime(int []processes, int n, int []bt)
{
int []wt = new int[n];
int []tat = new int[n];
int total_wt = 0, total_tat = 0;
//Function to find waiting time of all processes
findWaitingTime(processes, n, bt, wt);
//Function to find turn around time for all processes
findTurnAroundTime(processes, n, bt, wt, tat);
//Display processes along with all details
Console.Write("Processes 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];
Console.Write(" {0} ", (i + 1));
Console.Write(" {0} ", bt[i]);
Console.Write(" {0}", wt[i]);
Console.Write(" {0}\n", tat[i]);
}
float s = (float)total_wt /(float) n;
int t = total_tat / n;
Console.Write("Average waiting time = {0}", s);
Console.Write("\n");
Console.Write("Average turn around time = {0} ", t);
}
// Driver code
public static void Main(String[] args)
{
// process id's
int []processes = {1, 2, 3};
int n = processes.Length;
// Burst time of all processes
int []burst_time = {10, 5, 8};
findavgTime(processes, n, burst_time);
}
}
// This code contributed by Rajput-Ji
Javascript
输出：
Processes Burst time Waiting time Turn around time
1 10 0 10
2 5 10 15
3 8 15 23
Average waiting time = 8.33333
Average turn around time = 16要点：
- 非抢占式
- 平均等待时间不是最佳的
- 不能并行利用资源：导致 Convoy 效应（考虑有很多 IO 绑定进程和一个 CPU 绑定进程的情况。当 CPU 绑定进程获取 CPU 时，IO 绑定进程必须等待 CPU 绑定进程。IO 绑定进程可以最好先占用 CPU 一段时间，然后再使用 IO 设备）。