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#pragma once
template <class T>
class cAllocationPool
{
public:
class cStarvationCallbacks
{
public:
virtual ~cStarvationCallbacks() {}
/** Is called when the reserve buffer starts to be used */
virtual void OnStartUsingReserve() = 0;
/** Is called once the reserve buffer has returned to normal size */
virtual void OnEndUsingReserve() = 0;
/** Is called when the allocation pool is unable to allocate memory. Will be repeatedly
called if it does not free sufficient memory */
virtual void OnOutOfReserve() = 0;
};
virtual ~cAllocationPool() {}
/** Allocates a pointer to T */
virtual T * Allocate() = 0;
/** Frees the pointer passed in a_ptr, invalidating it */
virtual void Free(T * a_ptr) = 0;
/** Two pools compare equal if memory allocated by one can be freed by the other */
bool IsEqual(const cAllocationPool & a_Other) const noexcept
{
return ((this == &a_Other) || DoIsEqual(a_Other) || a_Other.DoIsEqual(*this));
}
friend bool operator == (const cAllocationPool & a_Lhs, const cAllocationPool & a_Rhs)
{
return a_Lhs.IsEqual(a_Rhs);
}
friend bool operator != (const cAllocationPool & a_Lhs, const cAllocationPool & a_Rhs)
{
return !a_Lhs.IsEqual(a_Rhs);
}
private:
virtual bool DoIsEqual(const cAllocationPool & a_Other) const noexcept = 0;
};
/** Allocates memory storing unused elements in a linked list. Keeps at least NumElementsInReserve
elements in the list unless malloc fails so that the program has a reserve to handle OOM. */
template <class T>
class cListAllocationPool:
public cAllocationPool<T>
{
public:
cListAllocationPool(std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> a_Callbacks, size_t a_MinElementsInReserve, size_t a_MaxElementsInReserve) :
m_MinElementsInReserve(a_MinElementsInReserve),
m_MaxElementsInReserve(a_MaxElementsInReserve),
m_Callbacks(std::move(a_Callbacks))
{
for (size_t i = 0; i < m_MinElementsInReserve; i++)
{
void * space = malloc(sizeof(T));
if (space == nullptr)
{
m_Callbacks->OnStartUsingReserve();
break;
}
m_FreeList.push_front(space);
}
}
virtual ~cListAllocationPool() override
{
while (!m_FreeList.empty())
{
free(m_FreeList.front());
m_FreeList.pop_front();
}
}
virtual T * Allocate() override
{
if (m_FreeList.size() <= m_MinElementsInReserve)
{
void * space = malloc(sizeof(T));
if (space != nullptr)
{
#if defined(_MSC_VER) && !defined(NDEBUG)
// The debugging-new that is set up using macros in Globals.h doesn't support the placement-new syntax used here.
// Temporarily disable the macro
#pragma push_macro("new")
#undef new
#endif
return new(space) T;
#if defined(_MSC_VER) && !defined(NDEBUG)
// Re-enable the debugging-new macro
#pragma pop_macro("new")
#endif
}
else if (m_FreeList.size() == m_MinElementsInReserve)
{
m_Callbacks->OnStartUsingReserve();
}
else if (m_FreeList.empty())
{
m_Callbacks->OnOutOfReserve();
// Try again until the memory is avalable
return Allocate();
}
}
// placement new, used to initalize the object
#if defined(_MSC_VER) && !defined(NDEBUG)
// The debugging-new that is set up using macros in Globals.h doesn't support the placement-new syntax used here.
// Temporarily disable the macro
#pragma push_macro("new")
#undef new
#endif
T * ret = new (m_FreeList.front()) T;
#if defined(_MSC_VER) && !defined(NDEBUG)
// Re-enable the debugging-new macro
#pragma pop_macro("new")
#endif
m_FreeList.pop_front();
return ret;
}
virtual void Free(T * a_ptr) override
{
if (a_ptr == nullptr)
{
return;
}
a_ptr->~T(); // placement destruct.
if (m_FreeList.size() >= m_MaxElementsInReserve)
{
free(a_ptr);
return;
}
m_FreeList.push_front(a_ptr);
if (m_FreeList.size() == m_MinElementsInReserve)
{
m_Callbacks->OnEndUsingReserve();
}
}
private:
/** The minimum number of elements to keep in the free list before malloc fails */
size_t m_MinElementsInReserve;
/** Maximum free list size before returning memory to the OS */
size_t m_MaxElementsInReserve;
std::list<void *> m_FreeList;
std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> m_Callbacks;
virtual bool DoIsEqual(const cAllocationPool<T> & a_Other) const noexcept override
{
return (dynamic_cast<const cListAllocationPool<T>*>(&a_Other) != nullptr);
}
};
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