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File indexing completed on 2021-02-14 14:31:51

0001 #ifndef Tracker_ChurnAllocator_H
0002 #define Tracker_ChurnAllocator_H
0003 #include <memory>
0004 
0005 template <typename T>
0006 class churn_allocator : public std::allocator<T> {
0007 public:
0008   using Base = std::allocator<T>;
0009   using pointer = typename Base::pointer;
0010   using size_type = typename Base::size_type;
0011 
0012   struct Cache {
0013     pointer cache = nullptr;
0014     bool gard = false;
0015   };
0016 
0017   static Cache &cache() {
0018     static thread_local Cache local;
0019     return local;
0020   }
0021 
0022   template <typename _Tp1>
0023   struct rebind {
0024     typedef churn_allocator<_Tp1> other;
0025   };
0026 
0027   pointer allocate(size_type n, const void *hint = nullptr) {
0028     Cache &c = cache();
0029     if (!c.gard)
0030       c.cache = std::allocator<T>::allocate(n, hint);
0031     c.gard = false;
0032     return c.cache;
0033   }
0034 
0035   void deallocate(pointer p, size_type n) {
0036     Cache &c = cache();
0037     if (p == c.cache)
0038       c.gard = true;
0039     else
0040       std::allocator<T>::deallocate(p, n);
0041   }
0042 
0043   churn_allocator() = default;
0044   churn_allocator(churn_allocator const &) = default;
0045   churn_allocator(churn_allocator &&) = default;
0046 
0047   template <class U>
0048   churn_allocator(const churn_allocator<U> &a) noexcept : std::allocator<T>(a) {}
0049 };
0050 
0051 #endif