SimpleHeap.h

/*
AutoHotkey

Copyright 2003-2008 Chris Mallett (support@autohotkey.com)

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
*/

#ifndef SimpleHeap_h
#define SimpleHeap_h

#include "stdafx.h" // pre-compiled headers

// In a large script (200 KB of text) of a typical nature, using SimpleHeap rather than malloc() saves
// nearly 200 KB of memory as shown by Task Manager's "VM Size" column (2384 vs. 2580 KB).
// This is because many callers allocate chunks of memory that are very small on average.  If each
// such chunk were allocated with malloc (or worse, "new"), the percentage of system overhead
// compared to the memory actually used for such blocks would be enormous (perhaps 40 bytes of
// overhead for each malloc(), even if it's only for 3 or 4 bytes).  In addition, SimpleHeap improves
// performance to the extent that it is faster than malloc(), which it almost certainly is.  Finally,
// the OS's overall memory fragmentation may be reduced, especially if the app uses this class over
// a long period of time (hours or days).

// The size of each block in bytes.  Use a size that's a good compromise
// of avg. wastage vs. reducing memory fragmentation and overhead.
// But be careful never to reduce it to something less than LINE_SIZE
// (the maximum line length that can be loaded -- currently 16K), otherwise,
// memory for that line might be impossible to allocate.
// Update: reduced it from 64K to 32K since many scripts tend to be small.
#define BLOCK_SIZE (32 * 1024) // Relied upon by Malloc() to be a multiple of 4.

class SimpleHeap
{
private:
	char *mBlock; // This object's memory block.  Although private, its contents are public.
	char *mFreeMarker;  // Address inside the above block of the first unused byte.
	size_t mSpaceAvailable;
	static UINT sBlockCount;
	static SimpleHeap *sFirst, *sLast;  // The first and last objects in the linked list.
	static char *sMostRecentlyAllocated; // For use with Delete().
	SimpleHeap *mNextBlock;  // The object after this one in the linked list; NULL if none.

	static SimpleHeap *CreateBlock();
	SimpleHeap();  // Private constructor, since we want only the static methods to be able to create new objects.
	~SimpleHeap();
public:
	static UINT GetBlockCount() {return sBlockCount;}
	static char *Malloc(char *aBuf, size_t aLength = -1); // Return a block of memory to the caller and copy aBuf into it.
	static char *Malloc(size_t aSize); // Return a block of memory to the caller.
	static void Delete(void *aPtr);
	//static void DeleteAll();
};

#endif