MemPool

 1 class MemPool {
 2     public:
 3         void init(int unitSize, int maxUnitNum) {
 4             long long size = unitSize * maxUnitNum;
 5             buffer = new char[size];
 6             memset(buffer, 0, sizeof(char) * size);
 7             for (int i = 0; i < size; ++i) {
 8                 available.push_back(buffer + i);
 9             }
10         }
11 
12         ~MemPool() {
13             if (buffer) {
14                 delete[] buffer;
15             }
16         }
17         // O(1)
18         void* alloc() {
19             if (available.empty()) return NULL;
20             char* ans = available.front();
21             available.pop_front();
22             allocated[ans] = 1;
23             return ans;
24         }
25 
26         // O(1)
27         void free(void *pUnit) {
28             char* tmp = (char*)pUnit;
29             if (allocated.find(tmp) == allocated.end()
30                     || allocated[tmp] == 0) return;
31             available.push_back(tmp);
32             allocated[tmp] = 0;
33         }
34     private:
35         unordered_map<char*, int> allocated;
36         list<char*> available;
37         char* buffer;
38 };