Design of page replacement simulation program (storage management in C language)

1. Introduction to the topic

Design a program in C language to simulate the execution process of a job. Assume that the job has a total of 320 instructions, that is, its address space is 32 pages, and all its pages have not been loaded into memory yet. During the simulation, if the accessed instruction is already in the memory, its physical address will be displayed and the next instruction will be transferred. If the accessed instruction has not been loaded into the memory, a page fault occurs. At this time, the number of page faults needs to be recorded, and the corresponding page is loaded into the memory. If the virtual pages of the job have been loaded into the four memory blocks, page replacement is required. Finally, its physical address is displayed, and the next instruction is transferred. After all 320 instructions have been executed, calculate and display the page fault rate that occurred during the job run.

2. Data structures used

/*定义内存中物理块的结构*/
struct memoryblock
{
    
    
	int pagenumber; // 页面号
	int access;     // 访问位
 	int time;       // 访问时间
	int counter;    // 访问次数
};
struct memoryblock M[4];

3. Program code description

void init()//初始化内存物理块
void random()//生成随机数
void FIFO()//先进先出置换算法
void CLOCK()//时钟置换算法
void LRU()//最近最久未使用置换算法
void LFU()//最近最少访问置换算法

Core code:

void random()
{
	srand((unsigned)time(NULL));
	int cnt = 0;
	command[cnt] = rand() % 320;
	cnt++;
	command[cnt] = command[cnt - 1] + 1;
	cnt++;
	while (cnt < 320)
	{
		command[cnt] = rand() % command[cnt - 2];
		cnt++;
		command[cnt] = command[cnt - 1] + 1;
		cnt++;
		command[cnt] = rand() % (320 - command[cnt - 1]) + command[cnt - 1];
		cnt++;
		command[cnt] = command[cnt - 1] + 1;
		cnt++;
	}
}
void oncefifo(int a)
{
	int i;
	int p=0;//指向队首的指令
	int b = a / 10;
	int flag=0;
	for (i = 0;i < 4;i++)
	{
		if (M[i].pagenumber == b)//表示页面在内存中
		{
			M[i].access = 1;
			flag = 1;
			break;
		}
		if (M[i].pagenumber == -1)//表示页面不在内存中，且物理块为空
		{
			M[i].access = 1;
			M[i].pagenumber = b;
			p = (p + 1) % 4;
			unfindpage++;
			flag = 1;
			break;
		}
	}
	if (flag == 0)//进行页面置换
	{
		M[p].pagenumber = b;
		M[p].access = 1;
		unfindpage++;
	}
}
void onceclock(int a)
{
	int i;
	int p=0;
	int b = a / 10;
	int flag = 0;
	for (i = 0;i < 4;i++)
	{
		if (M[i].pagenumber == b)//表示页面在内存中
		{
			M[i].access = 1;
			flag = 1;
			break;
		}
		if (M[i].pagenumber == -1)//表示页面不在内存中，且物理块为空
		{
			M[i].access = 1;
			M[i].pagenumber = b;
			p = (p + 1) % 4;
			unfindpage++;
			flag = 1;
			break;
		}
	}
	if (flag == 0)
	{
		while (M[p].access != 0)
		{
			M[p].access = 0;
			p = (p + 1) % 4;
		}
		M[p].pagenumber = b;
		M[p].access = 1;
		p = (p + 1) % 4;
		unfindpage++;
	}
}
void oncelru(int a)
{
	int b = a / 10;
	int flag = 0;
	int i,j;
	for (i = 0;i < 4;i++)
	{
		if (M[i].pagenumber == b)//页面在内存中，更新时间
		{
			M[i].time = 0;
			M[i].access = 1;
			flag = 1;
			for (j = 0;j < 4;j++)
			{
				if (j != i&&M[j].pagenumber != -1)//其他未被访问的页面的时间加一
				{
					M[j].time++;
				}
			}
			break;
		}
		if (M[i].pagenumber == -1)//页面不在内存中，且物理块为空
		{
			M[i].time = 0;
			M[i].pagenumber = b;
			M[i].access = 1;
			unfindpage++;
			flag = 1;
			for (j = 0;j < 4;j++)
			{
				if (j != i&&M[j].pagenumber != -1)
				{
					M[j].time++;
				}
			}
			break;
		}
	}
		if (flag == 0)//页面不在内存中,进行置换
		{
			sort(M, M + 4, cmp1);
			M[0].time=0;
			M[0].access = 1;
			M[0].pagenumber = b;
			unfindpage++;
			for (j = 1;j < 4;j++)
			{
				M[j].time++;
			}
		}
}
void oncelfu(int a)
{
	int b = a / 10;
	int flag = 1;
	int i;
	for (i = 0;i < 4;i++)
	{
		if (M[i].pagenumber == b)//页面在内存中
		{
			M[i].counter++;
			flag = 1;
			M[i].access = 1;
			break;
		}
		if (M[i].pagenumber = -1)
		{
			M[i].counter++;
			M[i].pagenumber = b;
			M[i].access = 1;
			flag = 1;
			unfindpage++;
			break;
		}
	}
	if (flag == 0)
	{
		sort(M, M + 4, cmp2);
		M[0].pagenumber = b;
		M[0].counter=1;
		M[i].access = 1;
		unfindpage++;
	}
}

4. Running results

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