操作系统 内存管理（最差 首次 最佳）

       最近操作系统上机，实现内存管理，就按照老师给的模板写了，了解相关的知识

/*所有的链表带有头节点，以便于排序*/

#include<stdio.h>
#include<stdlib.h>
#include<malloc.h>
#define PROCESS_NAME_LEN 32 /*进程名长度*/
#define MIN_SLICE 10 /*最小碎片的大小*/
#define DEFAULT_MEM_SIZE 1024 /*内存大小*/
#define DEFAULT_MEM_START 0 /*起始位置*/
/* 内存分配算法 */
#define MA_FF 1
#define MA_BF 2
#define MA_WF 3
int mem_size = DEFAULT_MEM_SIZE; /*内存大小*/
int ma_algorithm = MA_FF; /*当前分配算法*/
static int pid = 0; /*初始pid*/
int flag = 0; /*设置内存大小标志*/

/*描述每一个空闲块的数据结构*/
struct free_block_type {
int size;
int start_addr;
struct free_block_type *next;
};
/*指向内存中空闲块链表的首指针*/
struct free_block_type *free_block;
/*每个进程分配到的内存块的描述*/
struct allocated_block {
int pid;
int size;
int start_addr;
char process_name[PROCESS_NAME_LEN];
struct allocated_block *next;
};
/*进程分配内存块链表的首指针*/
struct allocated_block *allocated_block_head = NULL;

//函数声明
void display_menu();
int set_mem_size();
void set_algorithm();
void rearrange(int algorithm);
int new_process();
int allocate_mem(struct allocated_block *ab);
void kill_process();
int free_mem(struct allocated_block *ab);
int dispose(struct allocated_block *free_ab);
int display_mem_usage();
//allocated_block* find_process(int pid);
void rearrange_FF();
void rearrange_BF();
void rearrange_WF();

/*按FF算法重新整理内存空闲块链表*/
void rearrange_FF()
{
//请自行补充 m代表头，p。q分别代表交换的两个节点 n代表交换截至位置
struct free_block_type *p, *q, *m, *n;

if ( free_block->next->next != NULL)
{
n = NULL;
while (n != free_block->next->next)
{
m = free_block;
p = free_block->next;
q = p->next;
while (q != n)
{
if (p->start_addr > q->start_addr)
{
p->next = q->next;
q->next = p;
m->next = q;
}
m = m->next;
p = m->next;
q = p->next;
}
n = p;
}
}

}
/*按BF算法重新整理内存空闲块链表*/
void rearrange_BF()
{
//请自行补充

//请自行补充 m代表头，p。q分别代表交换的两个节点 n代表交换截至位置
struct free_block_type *p, *q, *m, *n;

if (free_block->next->next != NULL)
{
n = NULL;
while (n != free_block->next->next)
{
m = free_block;
p = free_block->next;
q = p->next;
while (q != n)
{
if (p->size > q->size)
{
p->next = q->next;
q->next = p;
m->next = q;
}
m = m->next;
p = m->next;
q = p->next;

}
n = p;
}
}
}
/*按WF算法重新整理内存空闲块链表*/
void rearrange_WF()
{
//请自行补充
//请自行补充 m代表头，p。q分别代表交换的两个节点 n代表交换截至位置
struct free_block_type *p, *q, *m, *n;

if (free_block->next->next != NULL)
{
n = NULL;
while (n != free_block->next->next)
{
m = free_block;
p = free_block->next;
q = p->next;
while (q != n)
{
if (p->size < q->size)
{
p->next = q->next;
q->next = p;
m->next = q;
}
m = m->next;
p = m->next;
q = p->next;
}
n = p;
}
}
}

//查找进程
struct allocated_block* find_process(int pid)
{
struct allocated_block *abb;
for (abb = allocated_block_head->next; abb && abb->pid != pid; abb = abb->next);
return abb;
}

//释放内存
int free_mem(struct allocated_block *ab)
{
struct free_block_type * p;
//分配空闲分区表的中的一个节点 每一次选择头节点后后面插入，并且完成之后查看当前算法，重新整理链表
p = (struct free_block_type *)malloc(sizeof(struct free_block_type));
p->next = free_block->next;
free_block->next = p;
p->size = ab->size;
p->start_addr = ab->start_addr;
return 1;
}

//释放要杀死进程的节点
int dispose(struct allocated_block *ab)
{
struct allocated_block *p;
for (p = allocated_block_head; p && p->next != ab; p = p->next);
p->next = ab->next;
free(ab);
return 1;
}

//杀死进程
void kill_process()
{
struct allocated_block *ab;
int pid;
printf("Kill Process, pid=");
scanf("%d", &pid);
getchar();
ab = find_process(pid);
if (ab != NULL)
{
free_mem(ab);
dispose(ab);
}
}

int allocate_mem(struct allocated_block *ab)
{
struct free_block_type *p, *q, *temp;
int sum = 0;
if (free_block->next == NULL)
{
printf("no memory");
return;
}
//当前算法进行整理内存
rearrange(ma_algorithm);

//根据当前算法在空闲分区链表中搜索合适空闲分区进行分配，分配时注意以下情况：
// 1. 找到可满足空闲分区且分配后剩余空间足够大，则分割
// 2. 找到可满足空闲分区且但分配后剩余空间（最小碎片化）比较小，则一起分配
// 3. 找不可满足需要的空闲分区但空闲分区之和能满足需要，则采用内存紧缩技术，进行空闲分区的合并，然后再分配
// 4. 在成功分配内存后，应保持空闲分区按照相应算法有序
// 5. 分配成功则返回1，否则返回-1

//如果首次适应 和最佳适应差不多 从链首开始查找，如果找到，则开始分配，如果没有找到，采用分区紧缩技术，如果可以分配，则分配，不能分配，返回-1
if (ma_algorithm == MA_FF || ma_algorithm == MA_BF)
{
//开始寻找符合条件的节点
for (p = free_block, q = p->next; q && q->size < ab->size; p = p->next, q = p->next);

//找到
if (q)
{
//判断是否达到最小碎片程度

if ((q->size - ab->size) <= MIN_SLICE)
{
//全部分配
ab->start_addr = q->start_addr;
ab->size = q->size;
//释放q节点
p->next = q->next;
free(q);
}
else
{
ab->start_addr = q->start_addr;
q->start_addr = q->start_addr + ab->size;
q->size = q->size - ab->size;
}
}
//开始内存紧缩
else
{
for (q = free_block->next; q; q = q->next)
{
sum += q->size;
if (sum >= ab->size)
{
break;
}
}
if (q)
{
//第一个空闲分区大小更改为sum，并且除了第一个，其他结点全部删除
free_block->next->size = sum;
p = free_block->next;
for (temp = p->next; temp != q; temp = p->next)
{
p->next = temp->next;
free(temp);
}
p->next = q->next;
free(q);

p->start_addr = p->start_addr + ab->size;
p->size = p->size - ab->size;
//如果剩余空间为0 则直接释放当前的空间
}
else

{
return -1;
}
}
}
//最差适应
else if (ma_algorithm == MA_WF)
{
//只需要找到第一个最大的空闲分区 如果满足，则分配，不满足则判断能否进行合并，如果可以，分配
if (free_block->next->size >= ab->size)
{
if (free_block->next->size - ab->size >= 10)
{
ab->start_addr = free_block->next->start_addr;
free_block->next->start_addr += ab->size;
free_block->next->size -= ab->size;
}
else

{
p = free_block->next;
free_block->next = p->next;
free(p);
}
}
else
{
for (q = free_block->next; q; q = q->next)
{
sum += q->size;
if (sum >= ab->size)
{
break;
}
}

if (q)
{
//第一个空闲分区大小更改为sum，并且除了第一个，其他结点全部删除
free_block->next->size = sum;
p = free_block->next;
for (temp = p->next; temp != q; temp = p->next)
{
p->next = temp->next;
free(temp);
}
p->next = q->next;
free(q);

ab->start_addr = free_block->next->start_addr;
p->start_addr = p->start_addr + ab->size;
p->size = p->size - ab->size;
//如果剩余空间为0 则直接释放当前的空间
}
else

{
return -1;
}

}
}

return 1;
}

//创建一个新的进程
int new_process()
{
struct allocated_block *ab;
int size;
int ret;
ab = (struct allocated_block *)malloc(sizeof(struct allocated_block));
if (!ab) exit(-5);
ab->next = NULL;
pid++;
sprintf(ab->process_name, "PROCESS-%02d", pid);
ab->pid = pid;
printf("Memory for %s:", ab->process_name);
scanf("%d", &size);
getchar();
if (size > 0) ab->size = size;
ret = allocate_mem(ab); /* 从空闲区分配内存，ret==1表示分配ok*/
/*如果此时allocated_block_head尚未赋值，则赋值*/
if ((ret == 1) && (allocated_block_head->next == NULL))
{
allocated_block_head->next = ab;
return 1;
}
/*分配成功，将该已分配块的描述插入已分配链表*/
else if (ret == 1)
{
ab->next = allocated_block_head->next;
allocated_block_head->next = ab;
return 2;
}
else if (ret == -1)
{
/*分配不成功*/
printf("Allocation fail\n");
free(ab);
return -1;
}
return 3;

}

int set_mem_size()
{
int size;
if (flag != 0)
{ //防止重复设置
printf("Cannot set memory size again\n");
return 0;
}
printf("Total memory size =");
scanf("%d", &size);
getchar();
if (size > 0)
{
mem_size = size;
free_block->next->size = mem_size;
}
flag = 1;
return 1;

}
void rearrange(int algorithm)
{
switch (algorithm)
{
case MA_FF: rearrange_FF(); break;
case MA_BF: rearrange_BF(); break;
case MA_WF: rearrange_WF(); break;
}
}

/* 设置当前的分配算法 */
void set_algorithm()
{
int algorithm;
printf("----------------------------------\n");
printf("\t1 - First Fit\n");
printf("\t2 - Best Fit \n");
printf("\t3 - Worst Fit \n");
scanf("%d", &algorithm);
getchar();
if (algorithm >= 1 && algorithm <= 3)
ma_algorithm = algorithm;
//按指定算法重新排列空闲区链表
rearrange(ma_algorithm);
}

//释放所有链表
void do_exit()
{
struct free_block_type *p;
struct allocated_block *q;
p = free_block->next;
q = allocated_block_head->next;
while (free_block->next != NULL)
{
free_block->next = p->next;
free(p);
p = free_block->next;
}
free(free_block);

while (allocated_block_head->next)
{
allocated_block_head->next = q->next;
free(q);
q = allocated_block_head->next;
}
free(allocated_block_head);
}

/*初始化空闲块，默认为一块，可以指定大小及起始地址*/
struct free_block_type* init_free_block(int mem_size) {
struct free_block_type *fb, *p;
struct allocated_block * q;
fb = (struct free_block_type *)malloc(sizeof(struct free_block_type));
p = (struct free_block_type *)malloc(sizeof(struct free_block_type));
q = (struct allocated_block*)malloc(sizeof(struct allocated_block));

if (fb == NULL || p == NULL || q == NULL)
{
printf("No mem\n");
return NULL;
}
q->next = NULL;
allocated_block_head = q;
p->size = mem_size;
p->start_addr = DEFAULT_MEM_START;
p->next = NULL;

fb->next = p;
return fb;
}

int display_mem_usage()
{
struct free_block_type *fbt = free_block->next;
struct allocated_block *ab = allocated_block_head->next;

if (fbt == NULL) return(-1);
printf("----------------------------------------------------------\n");

/* 显示空闲区 */
printf("Free Memory:\n");
printf("%20s %20s\n", " start_addr", " size");
while (fbt != NULL)
{
printf("%20d %20d\n", fbt->start_addr, fbt->size);
fbt = fbt->next;
}
/* 显示已分配区 */
printf("\nUsed Memory:\n");
printf("%10s %20s %10s %10s\n", "PID", "ProcessName", "start_addr", " size");
while (ab != NULL)
{
printf("%10d %20s %10d %10d\n", ab->pid, ab->process_name, ab->start_addr, ab->size);
ab = ab->next;
}
printf("----------------------------------------------------------\n");
return 0;
}

/*显示菜单*/
void display_menu()
{
printf("\n");
printf("1 - Set memory size (default=%d)\n", DEFAULT_MEM_SIZE);
printf("2 - Select memory allocation algorithm\n");
printf("3 - New process \n");
printf("4 - Terminate a process \n");
printf("5 - Display memory usage \n");
printf("0 - Exit\n");
}

int main(void)
{
char choice; pid = 0;
free_block = init_free_block(mem_size); //初始化空闲区

while (1)
{
display_menu(); //显示菜单
fflush(stdin);
choice = getchar();
fflush(stdin);
//获取用户输入
switch (choice)
{
case '1': set_mem_size(); break; //设置内存大小
case '2': set_algorithm(); flag = 1; break;//设置算法
case '3': new_process(); flag = 1; break;//创建新进程
case '4': kill_process(); flag = 1; break;//删除进程
case '5': display_mem_usage(); flag = 1; break; //显示内存使用
case '0': do_exit(); exit(0); //释放链表并退出
default: break;
}
}
return 0;
}

算法需要进行优化，很多地方重复太多，总的来说，理解了内存管理这一块