#ifndef _SLAB_ALLOCATOR_H_
#define _SLAB_ALLOCATOR_H_
#include <new>
#include <algorithm>
////////////////////////////////////////////////////////////
// A slab allocator allocate memory for many objects of the
// same time.
//
// When memory is needed for an object, it first see whether
// there are free objects in the freelist. If not, it then
// look at the current block. It will request a new block if
// necessary. The new allocated block is not split into the
// freelist immediately. Only deallocated objects will be put
// into the freelist.
//
// When the slab allocator is destroyed, all the blocks are
// freed. The allocator will NOT call either constructor
// or destructor.
////////////////////////////////////////////////////////////
template<typename T, size_t Block_size=4096>
class SlabAllocator
{
private:
struct Node
{
Node *next;
};
Node *m_blocks; // Allocated blocks chained together
char *m_block; // Current block used for allocating
size_t m_block_remain; // How many bytes remained for current block
Node *m_freelist; // Released objects are chained here
void get_new_block() {
Node *block = (Node *)operator new(Block_size);
// Link blocks for later release
block->next = m_blocks;
m_blocks = block;
char *mem = (char *)block;
// Skip the header used to link the blocks together
size_t skip = std::max(sizeof(Node), sizeof(T));
mem += skip;
m_block = mem;
m_block_remain = Block_size-skip;
}
public:
SlabAllocator()
:m_blocks(NULL), m_block(NULL), m_block_remain(0), m_freelist(NULL) {
}
~SlabAllocator() {
Node *next;
while (m_blocks != NULL) {
next = m_blocks->next;
delete m_blocks;
m_blocks = next;
}
}
// Allocate
T *allocate() {
if (m_freelist == NULL) {
if (m_block_remain < sizeof(T)) {
get_new_block();
}
T *res = (T *)m_block;
m_block += sizeof(T);
m_block_remain -= sizeof(T);
return res;
} else {
Node *res = m_freelist;
m_freelist = m_freelist->next;
return (T *)res;
}
}
// Release
void release(T *t) {
Node *obj = (Node *)t;
obj->next = m_freelist;
m_freelist = obj;
}
};
#endif /* _SLAB_ALLOCATOR_H_ */
