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#pragma once
#include <memory>
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;
};
/** 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, size_t NumElementsInReserve>
class cListAllocationPool:
public cAllocationPool<T>
{
public:
cListAllocationPool(std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> a_Callbacks):
m_Callbacks(std::move(a_Callbacks))
{
for (size_t i = 0; i < NumElementsInReserve; i++)
{
void * space = malloc(sizeof(T));
if (space == nullptr)
{
m_Callbacks->OnStartUsingReserve();
break;
}
m_FreeList.push_front(space);
}
}
virtual ~cListAllocationPool()
{
while (!m_FreeList.empty())
{
free (m_FreeList.front());
m_FreeList.pop_front();
}
}
virtual T * Allocate() override
{
if (m_FreeList.size() <= NumElementsInReserve)
{
void * space = malloc(sizeof(T));
if (space != nullptr)
{
return new(space) T;
}
else if (m_FreeList.size() == NumElementsInReserve)
{
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
T * ret = new (m_FreeList.front()) T;
m_FreeList.pop_front();
return ret;
}
virtual void Free(T * a_ptr) override
{
if (a_ptr == nullptr)
{
return;
}
// placement destruct.
a_ptr->~T();
m_FreeList.push_front(a_ptr);
if (m_FreeList.size() == NumElementsInReserve)
{
m_Callbacks->OnEndUsingReserve();
}
}
private:
std::list<void *> m_FreeList;
std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> m_Callbacks;
};
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