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  Templated Object Pool
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Hello flipcoders. I've been having fun with an idea for object pools. What I wanted was a basic object pool designed for fast alocation of fixed size objects. I required operations to create and destroy the object pool, a function to do a fast allocation from it, and also a fast delete (return to pool). Last of all, I required a variable to hold the pool contents, which is passed to the other routines so that the program knows which object pool I am referring to.

I came up with quite an elegant solution IMHO. The AllocateFromObjectPool function is very fast, at the expense of a slow setup in CreateObjectPool. You will notice that the pool is a parameter to every function, this is because I sneakily get the size etc from the variable's type. You can have as many different pools, of whatever types, as you like. Use it like this:

 struct blah {
   short a;
   int b;
   char c;
 };

blah *pool; CreateObjectPool(pool, 10);

blah *myitem = AllocateFromObjectPool(pool); // (myitem = new blah;) ReturnObjectToPool(pool, myitem); // (delete myitem;)

DeleteObjectPool(pool);



DO NOT try and access the items directly through the pointer to the pool for any reason! Only use these functions on it. It uses a free-list internally, stored at the address pointed to by the pool, so the items are offset in memory. I should probably have wrapped this up in a class to prevent that, but I haven't. Instead of suggesting that, how about DIY? My ultimate aim here is to inspire someone else into writing something even better. I made good use of structs and unions and templates and avoid having to do typecasts like (TItem***) - no I'm not kidding, that was my original plan!

I haven't tested this too extensively, but being quite short it's not likely to contain many bugs. It wont be thread-safe I guess.

Written on a Mac using Symantec C++ v8.6. Permission to use/copy/modify/distribute hereby granted. Do what you want with it - enjoy!

Keep the cotd alive people - contribute! [NZ]_i/\/\alc
(Malcolm)

Download Associated File: MyObjectPool.h (1,703 bytes)

#ifndef MY_OBJECTPOOL_H
#define MY_OBJECTPOOL_H

//Creates an object pool //pool: the variable to hold the pool //numObj: how many objects required in the pool template <class TItem> void CreateObjectPool(TItem *&pool, int numObj) { union TElement { TItem *next; TItem item; }; pool = (TItem*)(new char[sizeof(TElement) * numObj + sizeof(TItem*)]) struct TPool { TItem *freePtr; TElement items[1]; } *data = (TPool*)pool; data->freePtr = &data->items[0].item; for (int i=0; i<numObj-1; ++i) data->items[i].next = &data->items[i+1].item; data->items[numObj-1].next = NULL; }

//Destroy the object pool //pool: the variable holding the pool to destroy template <class TItem> void DeleteObjectPool(TItem *pool) { delete[] ((char*)pool); }

//This is essentially replaces your 'new' function //pool: the pool you wish to allocate from //returns: an object from the pool, or NULL template <class TItem> TItem *AllocateFromObjectPool(TItem *pool) { union TElement { TItem *next; TItem item; }; struct TPool { TItem *freePtr; TElement items[1]; } *data = (TPool*)pool; TItem *newObj = data->freePtr; if (newObj != NULL) data->freePtr = ((TElement*)newObj)->next; return newObj; }

//This is essentially replaces your 'delete' function //pool: the pool that the object came from //oldObj: an object from the pool to return template <class TItem> void ReturnObjectToPool(TItem *pool, TItem *oldObj) { union TElement { TItem *next; TItem item; }; struct TPool { TItem *freePtr; TElement items[1]; } *data = (TPool*)pool; ((TElement*)oldObj)->next = data->freePtr; data->freePtr = oldObj; }

#endif

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