From ee50790398791c38e563eee04cf12780fab74baf Mon Sep 17 00:00:00 2001
From: Tycho <work.tycho+git@gmail.com>
Date: Mon, 16 Jun 2014 15:12:50 +0100
Subject: Merge branch 'master' of github.com:mc-server/MCServer

---
 src/AllocationPool.h | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 src/AllocationPool.h

(limited to 'src/AllocationPool.h')

diff --git a/src/AllocationPool.h b/src/AllocationPool.h
new file mode 100644
index 000000000..5d749a79e
--- /dev/null
+++ b/src/AllocationPool.h
@@ -0,0 +1,109 @@
+
+#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::auto_ptr<typename cAllocationPool<T>::cStarvationCallbacks> a_Callbacks) :
+			m_Callbacks(a_Callbacks)
+		{
+			for (size_t i = 0; i < NumElementsInReserve; i++)
+			{
+				void * space = malloc(sizeof(T));
+				if (space == NULL)
+				{
+					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 != NULL)
+				{
+					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 == NULL) 
+			{
+				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::auto_ptr<typename cAllocationPool<T>::cStarvationCallbacks> m_Callbacks;
+};
-- 
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