A simple memory pool template
If you run into a situation that you need to allocate a specific object very frequently. Obviously the traditional way will cause the memory fragment because of frequent allocation on heap, and you will get more risk for failure of allocation after a certain running period. so this situation the memory pool definately is your best choice.
I got this situation on my open source project. A lot of client will connect and disconnect the server occasionally. I need to allocate a chunk of heap memory for each connecting, and recycle the memeory when disconnecting. so I came up with a very simple and effective memory pool to address this problem.Here is the code .
template <typename T > class MemoryPool {
public :
MemoryPool(int nSize) throw (std::bad_alloc&) : mnSize(nSize){
std::unique_ptr<T[]> lp (new T[mnSize]);
mArrayBuffer = std::move(lp);
mnFreeSize = mnSize;
for(int i = 0; i < mnSize ; i++)
mBitSet.push_back(false);
}
T* alloc() {
if(!mArrayBuffer)
return nullptr;
//check a empty slot in the bitset
for(int i = 0 ; i < mnSize ; i++)
{
if(mBitSet[i] == false)
{
mnFreeSize--;
mBitSet[i] = true;
return &mArrayBuffer[i];
}
}
return nullptr;
}
void free(T* np) {
if(!mArrayBuffer)
return ;
if(np != nullptr &&
( np >= &mArrayBuffer[0] && np <= &mArrayBuffer[mnSize-1]) ){
int offset = (np- &mArrayBuffer[0]) % sizeof(T);
mBitSet[offset] = false;
mnFreeSize++;
}
}
int GetFreeSize() {return mnFreeSize;}
private:
const int mnSize;
int mnFreeSize;
std::vector<bool> mBitSet;
std::unique_ptr<T[]> mArrayBuffer;
};By the way , in the first place I wanted to use the BitSet in place of Vector