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Memory Management GameEngine


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#1 EngineProgrammer   Members   -  Reputation: 295

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Posted 21 September 2012 - 09:27 AM

Hi everyone!!

I'm learning memory management for about 2 days now and I'm trying to create my own memory management for my game engine.

First I start with heap allocation.
If someone has some time to check if I'm doing OK please have a look at the code below.

But now that I have a Heap Allocator. How should I continue?
I heard something about pools and I've read a little bit about them but still don't have a clue what they should do.
Also, how can I make my HeapAllocator multi-thread safe?
I assume some of my heaps will give errors when I use multithreads?


Thanks in advance!
Kind regards,
Jonathan

This is the code I have at the moment:
///////////////////////////////////////////////////////////////////////////
// HeapAllocator.h
// Date: 21/09/2012
// Copyrights Bollaert Jonathan
///////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////
#ifndef HEAP_ALLOCATOR_H
#define HEAP_ALLOCATOR_H

#pragma once

#include "Types.h"
#include "Assert.h"
#include <iostream>
using namespace std;

template<typename T> CINLINE
T Align(T nData, size_t nAlign)
{
// More information: http://en.wikipedia.org/wiki/Data_structure_alignment
ASSERT((nAlign & (nAlign - 1)) == 0);
size_t size = ((size_t)nData + (nAlign - 1)) & ~(nAlign - 1);
return T(size);
}

namespace C2D1HeapAlloc
{
///////////////////////////////////////////////
// Heap System Allocator
///////////////////////////////////////////////
class HeapSysAllocator
{
public:
  static CVOID* SysAlloc(size_t size) {
   cout << "HeapSysAllocator has allocated a heap with size: " << size << " bytes." << endl;
   return malloc(size);
  }
  static CVOID SysDealloc(void* ptr) {
   cout << "HeapSysAllocator has deallocated a heap." << endl;
   free(ptr);
  }
};

///////////////////////////////////////////////
// Memory Usage
///////////////////////////////////////////////
struct MemoryUsage
{
  size_t m_MemAllocated, m_MemUsed;
  MemoryUsage(size_t nAlloc = 0, size_t nUsed = 0)
   :m_MemAllocated(nAlloc), m_MemUsed(nUsed)
  {
   Validate();
  }
  CINLINE CVOID Validate() {
   ASSERT(m_MemUsed <= m_MemAllocated);
  }
  CINLINE CVOID ClearMemory(){
   m_MemAllocated = m_MemUsed = 0;
  }
  CINLINE const size_t GetMemoryFree() const {
   return m_MemAllocated - m_MemUsed;
  }
  CINLINE const size_t GetMemoryAllocated() const {
   return m_MemAllocated;
  }
  CINLINE const size_t GetMemoryUsed() const {
   return m_MemUsed;
  }
};

///////////////////////////////////////////////
// Round up to next multiple of nAlign.
///////////////////////////////////////////////
CINLINE const size_t RoundUpTo(size_t nSize, size_t nAlign)
{
  ASSERT(nAlign > 0);
  nSize += nAlign - 1;
  return nSize - nSize % nAlign;
}

///////////////////////////////////////////////
// Heap Allocator
///////////////////////////////////////////////
template<CBOOL bMultiPage = true, typename SysAl = HeapSysAllocator>
class HeapAllocator: private SysAl
{
public:
  enum {DefaultAlignment = sizeof(void*)}; // 4 bytes
  enum {DefaultPageSize = 0x1000}; // 4 Kb
  HeapAllocator(size_t nPageSize = DefaultPageSize)
   :m_PageSize(nPageSize ? nPageSize : DefaultPageSize)
   ,m_PageList(nullptr)
  {
   cout << "HeapAllocator is being constructed on the stack with size: " << sizeof(*this) << " bytes." << endl;
  }
  ~HeapAllocator()
  {
   cout << "HeapAllocator is being deallocated." << endl;
   Clear();
  }

  ////////////////////////////
  // Raw memory allocation
  ////////////////////////////
  void* Allocate(size_t nSize, size_t nAlign = DefaultAlignment)
  {
   for(;;)
   {
	cout << "Attempting to find a heap..." << endl;
	// Try allocating from head page first
	if(m_PageList)
	{
	 cout << "Heap has been found." << endl;
	 cout << "Attempting to allocate: " << nSize << " bytes." << endl;
	 if(void* ptr = m_PageList->Allocate(nSize, nAlign))  {
	  m_Memory.m_MemUsed += nSize;
	  return ptr;
	 }
	 if(m_PageList->m_pNext && m_PageList->m_pNext->GetMemoryFree() > m_PageList->GetMemoryFree())
	 {
	  SortPage(m_PageList);
	  Validate();
	  if(void* ptr = m_PageList->Allocate(nSize, nAlign)) {
	   m_Memory.m_MemUsed += nSize;
	   return ptr;
	  }
	 }
	 cout << "Allocating requested memory FAILED." << endl;
	 if(!bMultiPage)
	  return 0;
	 cout << "Heap can not store the required size." << endl;
	}
	else
	{
	 cout << "No heap has been found!" << endl;
	}
	// Allocate the new page of the required size.
	int nAllocSize = sizeof(PageNode) + nAlign - 1 + RoundUpTo(nSize, m_PageSize);
	cout << "Attempting to allocate a heap..." << endl;
	void* pAlloc = this->SysAlloc(nAllocSize);
	PageNode* pPageNode = new(pAlloc) PageNode(nAllocSize);
	// Insert at head of list
	pPageNode->m_pNext = m_PageList;
	m_PageList = pPageNode;
	m_Memory.m_MemAllocated += nAllocSize;
	Validate();
   }
  }
  CVOID Deallocate(void* ptr, size_t nSize)
  {
   cout << "Attempting to deallocate memory..." << endl;
   ASSERT(CheckPtr(ptr));
   ASSERT(m_Memory.m_MemUsed >= nSize);
   m_Memory.m_MemUsed -= nSize;
   cout << "A memory with size: " << nSize << " bytes has been deallocated." << endl;
  }

  ////////////////////////////
  // Maintenance
  ////////////////////////////
  CINLINE const MemoryUsage GetTotalMemory() const {
   m_Memory;
  }
  struct PageNodeHandle {};
  PageNodeHandle* RemovePages() {
   // Remove the pages from the object.
   PageNodeHandle* pPageNode;
   Validate();
   pPageNode = m_PageList;
   m_PageList = 0;
   m_Memory.ClearMemory();
   return pPageNode;
  }
  CVOID FreeMemory(PageNodeHandle* handle)
  {
   PageNode* pPageNode = static_cast<PageNode*>(handle);
   // Loop through all the pages, freeing the memory.
   while(pPageNode != nullptr)
   {
	// Read the "next" pointer before deleting.
	PageNode* pNext = pPageNode->m_pNext;
	// Delete the current page
	this->SysDealloc(pPageNode);
	// Mode to the next page in the list
	pPageNode = pNext;
   }
  }
  CVOID Clear()
  {
   PageNodeHandle* pPageNode;
   Validate();
  
   // Remove the pages from the object.
   pPageNode = RemovePages();
  
   // Loop through all the pages, freeing the memory.
   FreeMemory(pPageNode);
  }
  CVOID Reset()
  {
   Validate();
   size_t nPrevSize = ~0;
   for(PageNode** ppPage = &m_PageList; *ppPage; )
   {
	(*ppPage)->Reset();
	if((*ppPage)->GetMemoryAlloc() > nPrevSize) {
	 // Move page to sorted location near beginning.
	 SortPage(*ppPage);
	 // ppPage is now next page, so continue loop.
	 continue;
	}
	nPrevSize = (*ppPage)->GetMemoryAlloc();
	ppPage = &(*ppPage)->pNext;
   }
   m_Memory.m_MemUsed = 0;
   Validate();
  }
  CBOOL CheckPtr(void* ptr) const
  {
   if(!ptr)
	return true;
   for(PageNode* pNode = m_PageList; pNode; pNode = pNode->m_pNext) {
	if(pNode->CheckPtr(ptr))
	 return true;
   }
   return false;
  }
  CVOID Validate()
  {
   MemoryUsage MemCheck;
   for(PageNode* pPage = m_PageList; pPage; pPage = pPage->m_pNext) {
	pPage->Validate();
	if(pPage != m_PageList && pPage->m_pNext)
	 ASSERT(pPage->GetMemoryFree() >= pPage->m_pNext->GetMemoryFree());
	MemCheck.m_MemAllocated += pPage->GetMemoryAllocated();
	MemCheck.m_MemUsed += pPage->GetMemoryUsed();
   }
   ASSERT(MemCheck.m_MemAllocated == m_Memory.m_MemAllocated);
   ASSERT(MemCheck.m_MemUsed >= m_Memory.m_MemUsed);
  }

protected:
  struct PageNode : PageNodeHandle
  {
   PageNode* m_pNext;
   char* m_pEndAlloc;
   char* m_pEndUsed;
   CINLINE char* StartUsed() const {
	return (char*)(this+1);
   }
   PageNode(size_t nAlloc) {
	m_pNext = nullptr;
	m_pEndAlloc = (char*)this + nAlloc;
	m_pEndUsed = StartUsed();
   }
   void* Allocate(size_t nSize, size_t nAlign) {
	// Align current mem
	char* pNew = Align(m_pEndUsed, nAlign);
	if(pNew + nSize > m_pEndAlloc)
	 return 0;
	m_pEndUsed = pNew + nSize;
	cout << "Memory has been allocated with size: " << nSize << " bytes." << endl;
	return pNew;
   }
  
   CINLINE CVOID Reset() {
	m_pEndUsed = StartUsed();
   }
   CINLINE const size_t GetMemoryAllocated() const {
	return m_pEndAlloc - (char*)this;
   }
   CINLINE const size_t GetMemoryUsed() const {
	return m_pEndUsed - StartUsed();
   }
   CINLINE const size_t GetMemoryFree() const {
	return m_pEndAlloc - m_pEndUsed;
   }
   CINLINE CVOID Validate() const {
	ASSERT(m_pEndAlloc >= (char*)this);
	ASSERT(m_pEndUsed >= StartUsed() && m_pEndUsed <= m_pEndAlloc);
   }
   CINLINE CBOOL CheckPtr(void* ptr) const {
	return (char*)ptr >= StartUsed() && (char*)ptr < m_pEndUsed;
   }
  };

  CVOID SortPage(PageNode* rpPage) {
   // Unlink rpPage.
   PageNode* pPage = rpPage;
   rpPage = pPage->m_pNext;
   // Insert into list based on free memory.
   PageNode** ppBefore = &m_PageList;
   while (*ppBefore && (*ppBefore)->GetMemoryFree() > pPage->GetMemoryFree())
	ppBefore = &(*ppBefore)->m_pNext;
   // Link before rpList.
   pPage->m_pNext = *ppBefore;
   *ppBefore = pPage;
  }

private:
  MemoryUsage  m_Memory; // Track memory allocated and used
  const size_t m_PageSize; // Pages allocated at this size
  PageNode*  m_PageList; // All allocated pages
};
}

#endif // HEAP_ALLOCATOR_H

Some of you may think "I have seen this kind of code before...."
Well got all the code from all of these:
- CryEngine open source SDK
- Standard Library C++ ~by Sutter
- Internet: http://www.cantrip.org/wave12.html
http://www.bogotobogo.com/cplusplus/memoryallocation.php
http://www.codeguru.com/cpp/cpp/cpp_mfc/stl/article.php/c4079/Allocators-STL.htm

Sponsor:

#2 larspensjo   Members   -  Reputation: 1526

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Posted 21 September 2012 - 10:21 AM

I heard something about pools and I've read a little bit about them but still don't have a clue what they should do.

This is a technique used for special circumstances, it is not always the best solution.

If your application frequently allocates and frees a memory chunk of the same size, then you can arrange to have a list of free memory blocks of this size, possibly in a linked list. This can be very efficient (in time).
Current project: Ephenation.
Sharing OpenGL experiences: http://ephenationopengl.blogspot.com/

#3 web383   Members   -  Reputation: 696

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Posted 21 September 2012 - 11:09 AM

Molecular Musings has several blogs on memory allocation strategies, including pool allocator and linear allocator.




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