127 lines
2.5 KiB
C++
127 lines
2.5 KiB
C++
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#pragma once
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#include <memory>
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template <class T>
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class cAllocationPool
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{
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public:
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class cStarvationCallbacks
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{
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public:
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virtual ~cStarvationCallbacks() {}
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/** Is called when the reserve buffer starts to be used */
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virtual void OnStartUsingReserve() = 0;
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/** Is called once the reserve buffer has returned to normal size */
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virtual void OnEndUsingReserve() = 0;
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/** Is called when the allocation pool is unable to allocate memory. Will be repeatedly
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called if it does not free sufficient memory */
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virtual void OnOutOfReserve() = 0;
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};
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virtual ~cAllocationPool() {}
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/** Allocates a pointer to T */
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virtual T * Allocate() = 0;
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/** Frees the pointer passed in a_ptr, invalidating it */
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virtual void Free(T * a_ptr) = 0;
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};
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/** Allocates memory storing unused elements in a linked list. Keeps at least NumElementsInReserve
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elements in the list unless malloc fails so that the program has a reserve to handle OOM. */
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template <class T, size_t NumElementsInReserve>
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class cListAllocationPool:
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public cAllocationPool<T>
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{
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public:
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cListAllocationPool(std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> a_Callbacks):
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m_Callbacks(std::move(a_Callbacks))
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{
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for (size_t i = 0; i < NumElementsInReserve; i++)
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{
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void * space = malloc(sizeof(T));
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if (space == nullptr)
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{
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m_Callbacks->OnStartUsingReserve();
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break;
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}
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m_FreeList.push_front(space);
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}
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}
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virtual ~cListAllocationPool()
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{
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while (!m_FreeList.empty())
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{
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free (m_FreeList.front());
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m_FreeList.pop_front();
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}
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}
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virtual T * Allocate() override
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{
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if (m_FreeList.size() <= NumElementsInReserve)
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{
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void * space = malloc(sizeof(T));
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if (space != nullptr)
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{
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return new(space) T;
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}
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else if (m_FreeList.size() == NumElementsInReserve)
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{
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m_Callbacks->OnStartUsingReserve();
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}
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else if (m_FreeList.empty())
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{
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m_Callbacks->OnOutOfReserve();
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// Try again until the memory is avalable
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return Allocate();
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}
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}
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// placement new, used to initalize the object
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T * ret = new (m_FreeList.front()) T;
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m_FreeList.pop_front();
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return ret;
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}
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virtual void Free(T * a_ptr) override
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{
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if (a_ptr == nullptr)
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{
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return;
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}
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// placement destruct.
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a_ptr->~T();
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m_FreeList.push_front(a_ptr);
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if (m_FreeList.size() == NumElementsInReserve)
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{
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m_Callbacks->OnEndUsingReserve();
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}
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}
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private:
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std::list<void *> m_FreeList;
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std::unique_ptr<typename cAllocationPool<T>::cStarvationCallbacks> m_Callbacks;
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};
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