C語言可以使用alloc從棧上動態分配內存。
內存碎片
Malloc/free或者new/delete大量使用會造成內存碎片,這種碎片形成的機理如下:
內存碎片一般是由於空閑的內存空間比要連續申請的空間小,導致這些小內存塊不能被充分的利用,舉個例子:
如果有100個單位的連續空閑內存,那么先申請3單元的連續內存,再申請50單元的內存,這時釋放一開始的3單元的內存。這時,如果你一直申請比三單元大的內存單元,那么開始的那連續的三單元就一直不能被使用。
一個簡單的內存池的寫法:
struct memblock
{
int used;
void* data;
struct memblock* next;
struct memblock* createnext;
};
struct mempool
{
int size;//memblock大小
int unused;//空閑的memblock大小
int datasize;//每次分配的數據大小(就是memblock.data)
struct memblock* free_linkhead;//空閑memblock鏈表頭
struct memblock* create_linkhead;//所有創建的memblock鏈表頭,內存池釋放的時候使用,防止內存池釋放的似乎還有memblock未歸還的情況
};
typedef void (*free_callback)(void*);//釋放回調函數,釋放membloc.data用,可以簡單的直接用free函數
void mempool_init(int initialSize,int datasize);//初始化mempool
void mempool_dealloc(struct mempool* pool,free_callback callback);//釋放mempool
void* mempool_get(struct mempool* pool);//獲取一個memblock
void mempool_release(struct mempool* pool,struct memblock* block);//歸還一個memblock
/*********************************
* mempool
* ******************************/
//malloc一個memblock
static struct memblock* mempool_allocblock( struct mempool* pool );
//------------------implement--------
void*
mempool_init( int initialSize, int datasize )
{
struct mempool* pool = malloc( sizeof( struct mempool ) );
pool->unused = 0;
pool->datasize = datasize;
pool->free_linkhead = NULL;
//預先初始化initialSize個內存塊
pool->create_linkhead = NULL;
int i;
for ( i = 0; i < initialSize; i++ ) {
struct memblock* block = mempool_allocblock( pool );
mempool_release( pool, block );
}
return ( pool );
}
void
mempool_dealloc( struct mempool* pool, free_callback callback )
{
struct memblock* block = NULL;
//將所有創建的memblock釋放了
while ( pool->create_linkhead != NULL ) {
block = pool->create_linkhead;
pool->create_linkhead = pool->create_linkhead->createnext;
//執行free回調。
if ( callback ) {
( *callback )( block->data );
}
free( block );
}
free( pool );
L_DEBUG( "%s:size(%d),unused(%d)", __func__, pool->size, pool->unused );
}
static struct memblock*
mempool_allocblock( struct mempool* pool )
{
struct memblock* block = malloc( sizeof( struct memblock ) );
block->data = malloc( sizeof( pool->datasize ) );
block->next = NULL;
block->used = 1;//表示已使用
//加入所有創建的memblock的鏈表頭
block->createnext = pool->create_linkhead;
pool->create_linkhead = block;
pool->size++;
return ( block );
}
void
mempool_release( struct mempool* pool, struct memblock* block )
{
if ( block == NULL ) {
L_WARN( "%s:release a NULL!", __func__ );
return;
}
if ( block->used != 1 ) {
L_WARN( "%s:used!=1", __func__ );
return;
}
//將歸還的內存塊放到空閑鏈表頭。
block->used = 0;//表示空閑
block->next = pool->free_linkhead;
pool->free_linkhead = block;
pool->unused++;//空閑數+1
}
void*
mempool_get( struct mempool* pool )
{
struct memblock* block = NULL;
if ( pool->free_linkhead ) {
//從空閑鏈表頭取出一個內存塊
block = pool->free_linkhead;
pool->free_linkhead = pool->free_linkhead->next;
block->next = NULL;
block->used = 1;//表示已使用
pool->unused--;//空閑內存塊數-1
}
else {
//沒有空閑的內存塊,創建一個
block = mempool_allocblock( pool );
}
return ( block );
}