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#pragma once
 
#include "pool.h" 
#include "alloc.h" 
 
#include <util/generic/utility.h>
#include <util/generic/intrlist.h> 
 
class TFixedSizeAllocator { 
    struct TAlloc: public TIntrusiveSListItem<TAlloc> { 
        inline void* ToPointer() noexcept {
            return this; 
        } 
 
        static inline TAlloc* FromPointer(void* ptr) noexcept {
            return (TAlloc*)ptr; 
        } 
 
        static constexpr size_t EntitySize(size_t alloc) noexcept {
            return Max(sizeof(TAlloc), alloc); 
        } 
 
        static constexpr size_t EntityAlign(size_t align) noexcept {
            return Max(alignof(TAlloc), align);
        }

        static inline TAlloc* Construct(void* ptr) noexcept {
            return (TAlloc*)ptr; 
        } 
    }; 
 
public: 
    using IGrowPolicy = TMemoryPool::IGrowPolicy;
 
    TFixedSizeAllocator(size_t allocSize, IAllocator* alloc)
        : TFixedSizeAllocator(allocSize, alignof(TAlloc), TMemoryPool::TExpGrow::Instance(), alloc)
    { 
    } 
 
    TFixedSizeAllocator(size_t allocSize, size_t alignSize, IAllocator* alloc)
        : TFixedSizeAllocator(allocSize, alignSize, TMemoryPool::TExpGrow::Instance(), alloc)
    {
    }

    TFixedSizeAllocator(size_t allocSize, IGrowPolicy* grow, IAllocator* alloc)
        : TFixedSizeAllocator(allocSize, alignof(TAlloc), grow, alloc)
    {
    }

    TFixedSizeAllocator(size_t allocSize, size_t alignSize, IGrowPolicy* grow, IAllocator* alloc)
        : Pool_(allocSize, grow, alloc) 
        , AlignSize_(TAlloc::EntityAlign(alignSize))
        , AllocSize_(TAlloc::EntitySize(allocSize))
    { 
    } 
 
    inline void* Allocate() { 
        if (Y_UNLIKELY(Free_.Empty())) {
            return Pool_.Allocate(AllocSize_, AlignSize_);
        } 
 
        return Free_.PopFront()->ToPointer(); 
    } 
 
    inline void Release(void* ptr) noexcept {
        Free_.PushFront(TAlloc::FromPointer(ptr)); 
    } 
 
    inline size_t Size() const noexcept {
        return AllocSize_; 
    } 
 
private: 
    TMemoryPool Pool_; 
    const size_t AlignSize_;
    const size_t AllocSize_; 
    TIntrusiveSList<TAlloc> Free_; 
}; 
 
template <class T> 
class TSmallObjAllocator { 
public: 
    using IGrowPolicy = TFixedSizeAllocator::IGrowPolicy;
 
    inline TSmallObjAllocator(IAllocator* alloc) 
        : Alloc_(sizeof(T), alignof(T), alloc)
    { 
    } 
 
    inline TSmallObjAllocator(IGrowPolicy* grow, IAllocator* alloc) 
        : Alloc_(sizeof(T), alignof(T), grow, alloc)
    { 
    } 
 
    inline T* Allocate() { 
        return (T*)Alloc_.Allocate(); 
    } 
 
    inline void Release(T* t) noexcept {
        Alloc_.Release(t); 
    } 
 
private: 
    TFixedSizeAllocator Alloc_; 
}; 
 
template <class T> 
class TObjectFromPool { 
public: 
    struct THeader {
        void* Pool;
        // Can't just use T because THeader must be standard layout type for offsetof to work.
        alignas(T) char Obj[sizeof(T)];
    };
    using TPool = TSmallObjAllocator<THeader>;
 
    inline void* operator new(size_t, TPool* pool) { 
        THeader* ret = pool->Allocate();
        ret->Pool = pool;
        return &ret->Obj;
    } 
 
    inline void operator delete(void* ptr, size_t) noexcept {
        DoDelete(ptr); 
    } 
 
    inline void operator delete(void* ptr, TPool*) noexcept {
        /* 
         * this delete operator can be called automagically by compiler 
         */ 
 
        DoDelete(ptr); 
    } 
 
private: 
    static inline void DoDelete(void* ptr) noexcept {
        static_assert(std::is_standard_layout<THeader>::value, "offsetof is only defined for standard layout types");
        THeader* header = (THeader*)((char*)ptr - offsetof(THeader, Obj));
        ((TPool*)header->Pool)->Release(header);
    } 
};