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/*********************************************************************************************
模块功能：ipanel内存分配释放。由于ipanel分配内存块较大，当操作系统内存碎片过多，且没有及时清理
的情况下，容易出现分配失败的情况，这时需要事先独立分配一块内存，提供给ipanel自身管理
模块描述：加入内存块头信息，存放分配内存块的大小、上下已用内存块头信息节点位置，采用链表管理
分配优先：检查memBaseAddr是否为第一节点（first），否，则尝试在memBaseAddr进行分配 ->
遍历链表，检查两已用内存块之间是否有可用空间，如有并大于等于分配大小，则进行分配 ->
在链表最后节点之后的剩余空间进行分配
改进权衡：
1、采用独立的空间存放内存块头信息
2、遍历所有已用内存块头信息链表，找到两已用内存块之间的可用空间最接近于要分配内存的大
小，并在该处进行分配，这样ipanel自身内存管理的碎片更少，但所耗的时间更长
3、直接在链表最后节点之后的剩余空间进行分配，当模块分配释放模式为malloc->malloc->
malloc->malloc->...->free->free->free->free时，推荐采用这种分配模式
*********************************************************************************************/
#include "stdafx.h"
#include <stdio.h>
#include <malloc.h>
void *memBaseAddr = NULL;//可分配内存的首地址
unsigned int totalMemSize = 0;//可分配内存的总大小
struct mem_block_info {
unsigned int size;//等于实际分配内存大小加上结构体mem_block_info的大小
struct mem_block_info *preview;//存放上已用内存块的头信息节点位置
struct mem_block_info *next;//存放下已用内存块的头信息节点位置
};
struct mem_block_info *first = NULL;//链表头节点
/*初始化可分配内存的base address和memory size*/
void my_set_mem_base_addr(void *addr, int size)
{
memBaseAddr = addr;
totalMemSize = size;
}
/*释放已用内存，删除内存块头信息节点*/
void free_used_mem(struct mem_block_info *used)
{
if (used == first)
first = first->next;
else
used->preview->next = used->next;
}
/*遍历链表，寻找可用空间。返回已分配空间头信息节点*/
struct mem_block_info *search_available_mem(unsigned int size /*[in]: 要求分配空间大小*/)
{
unsigned int freeSize;
struct mem_block_info *result = NULL;
struct mem_block_info *current = first;
if (size % 4)
size = (size/4 + 1) * 4; //强制四字节对齐
if (!first)
{
//当内存是第一次分配时
freeSize = totalMemSize;
if (size + sizeof(struct mem_block_info) > freeSize)
{
result = NULL;
return result;
}
else
{
result = (struct mem_block_info *)memBaseAddr;
result->preview = NULL;
result->next = NULL;
result->size = size + sizeof(struct mem_block_info);
first = result;
return result;
}
}
if (memBaseAddr != first)
{
//检查第一个节点是否从memBaseAddr开始，如果否，优先从memBaseAddr进行分配
freeSize = (unsigned int)first - (unsigned int)memBaseAddr;
if (size + sizeof(struct mem_block_info) <= freeSize)
{
result = (struct mem_block_info *)memBaseAddr;
result->preview = NULL;
result->next = first;
result->size = size + sizeof(struct mem_block_info);
first = result;
return result;
}
}
while (current)
{
if (current->next == NULL)
{
//优先从两内存块节点之间的剩余空间分配，如果都没有足够空间，则从后面的剩余内存进行分配
freeSize = totalMemSize - ((unsigned int)current - (unsigned int)memBaseAddr + current->size);
if (size + sizeof(struct mem_block_info) > freeSize)
{
result = NULL;
return result;
}
else
{
result = (struct mem_block_info *)((unsigned int)current + current->size);
result->preview = current;
result->next = NULL;
result->size = size + sizeof(struct mem_block_info);
current->next = result;
return result;
}
}
else
{
//检查两块已分配的内存块之间是否有足够的空间，如果有，则分配
freeSize = (unsigned int)(current->next) - (unsigned int)current - current->size;
if (size + sizeof(struct mem_block_info) <= freeSize)
{
result = (struct mem_block_info *)((unsigned int)current + current->size);
result->size = size + sizeof(struct mem_block_info);
result->preview = current;
result->next = current->next;
current->next = result;
return result;
}
}
//否，则继续遍历
current = current->next;
}
return result;
}
void *my_malloc(int memsize)
{
struct mem_block_info *result = NULL;
result = search_available_mem(memsize);
if (!result)
return NULL;
return (void *)((unsigned int)result + sizeof(struct mem_block_info));
}
void my_free(void* memptr)
{
struct mem_block_info *used;
if (memptr)
{
used = (struct mem_block_info *)((unsigned int)memptr - sizeof(struct mem_block_info));
free_used_mem(used);
}
}
int _tmain(int argc, _TCHAR* argv[])
{
//测试程序
printf("struct mem_block_info size %d\n", sizeof(struct mem_block_info));
struct mem_block_info *rc;
void *ptr = NULL;
void *first = NULL;
void *second = NULL;
void *third = NULL;
void *fourth = NULL;
void *fineth = NULL;
unsigned int totalmem = 0xa00000;
ptr = (void *)malloc(totalmem);
my_set_mem_base_addr(ptr, totalmem);
first = my_malloc(0x10000);
second = my_malloc(0x20000);
third = my_malloc(0x40);
my_free(second);
fourth = my_malloc(0x800);
my_free(first);
fineth = my_malloc(0x40000);
*(unsigned int *)fineth = 0x40;
printf("*fineth 0x%x\n", *(unsigned int *)fineth);
rc = (struct mem_block_info *)((unsigned int)fourth - sizeof(struct mem_block_info));
printf("fineth struct info: size 0x%x, next %p", rc->size, rc->next);
return 0;
}
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PS：
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近日又研究了一下Unix下的内存分配策略，才晓得常见的策略有：
first-fit、next-fit、best-fit、quick-fit
quick-fit速度快，但空间浪费大，明显不适合我们模块这种情形
best-fit内存碎片少，但时间消耗大，在内存紧张的情形下可用
first-fit是我如今采用的一个策略
next-fit我感觉比first-fit有很大的改进，特别适用于内存会被多次分配释放的情形 |
如果今后要进行改进的话，可以考虑将next-fit和best-fit结合
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