CachedOSPageAllocator.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "HAL/CriticalSection.h"
#include "HAL/PlatformMemory.h"
 
struct FCachedOSPageAllocator
{
protected:
    struct FFreePageBlock
    {
        void*  Ptr;
        SIZE_T ByteSize;
 
        FFreePageBlock()
        {
            Ptr      = nullptr;
            ByteSize = 0;
        }
    };
 
    void* AllocateImpl(SIZE_T Size, uint32 CachedByteLimit, FFreePageBlock* First, FFreePageBlock* Last, uint32& FreedPageBlocksNum, SIZE_T& CachedTotal, FCriticalSection* Mutex);
    void FreeImpl(void* Ptr, SIZE_T Size, uint32 NumCacheBlocks, uint32 CachedByteLimit, FFreePageBlock* First, uint32& FreedPageBlocksNum, SIZE_T& CachedTotal, FCriticalSection* Mutex, bool ThreadIsTimeCritical);
    void FreeAllImpl(FFreePageBlock* First, uint32& FreedPageBlocksNum, SIZE_T& CachedTotal, FCriticalSection* Mutex);
 
    static bool IsOSAllocation(SIZE_T Size, uint32 CachedByteLimit)
    {
        return (FPlatformMemory::BinnedPlatformHasMemoryPoolForThisSize(Size) || Size > CachedByteLimit / 4);
    }
};
 
template <uint32 NumCacheBlocks, uint32 CachedByteLimit>
struct TCachedOSPageAllocator : private FCachedOSPageAllocator
{
    TCachedOSPageAllocator()
        : CachedTotal(0)
        , FreedPageBlocksNum(0)
    {
    }
 
    FORCEINLINE void* Allocate(SIZE_T Size, uint32 AllocationHint = 0, FCriticalSection* Mutex = nullptr)
    {
        return AllocateImpl(Size, CachedByteLimit, FreedPageBlocks, FreedPageBlocks + FreedPageBlocksNum, FreedPageBlocksNum, CachedTotal, Mutex);
    }
 
    void Free(void* Ptr, SIZE_T Size, FCriticalSection* Mutex = nullptr, bool ThreadIsTimeCritical = false)
    {
        return FreeImpl(Ptr, Size, ThreadIsTimeCritical ? NumCacheBlocks*2 : NumCacheBlocks, CachedByteLimit, FreedPageBlocks, FreedPageBlocksNum, CachedTotal, Mutex, ThreadIsTimeCritical);
    }
    void FreeAll(FCriticalSection* Mutex = nullptr)
    {
        return FreeAllImpl(FreedPageBlocks, FreedPageBlocksNum, CachedTotal, Mutex);
    }
    // Refresh cached os allocator if needed. Does nothing for this implementation
    void Refresh()
    {
 
    }
    void UpdateStats()
    {
 
    }
    uint64 GetCachedFreeTotal()
    {
        return CachedTotal;
    }
 
    bool IsOSAllocation(SIZE_T Size)
    {
        return FCachedOSPageAllocator::IsOSAllocation(Size, CachedByteLimit);
    }
 
private:
    FFreePageBlock FreedPageBlocks[NumCacheBlocks*2];
    SIZE_T         CachedTotal;
    uint32         FreedPageBlocksNum;
};