Re: [Boost-users] [pool] pool allocator: customizing and memory usage

On Feb 19, 2008 5:25 AM, Lang Stefan wrote:

Hello all,

I've been trying to integrate pool allocators for lists within our project, but early test runs turned up quite a surprising number of questions and problems. I've tried to resolve those issues by closely regarding the documentation, debugging, and - finally - checking this list for threads that potentially answer my questions, but unfortunately I found that on this list more questions were raised than answered.

Specifically, I noticed that Stephen Cleary doesn't seem to frequent this list, or has stopped doing so some 5 or 6 years ago.

Indeed, this is very unfortunate.

Nevertheless maybe there are other people out there who can answer one or more of my questions, so here I go:

1. When using fast_pool_allocator for std::list<> I see no way to influence the blocksize being used for the next allocation. Since our application handles huge lists I cannot have fast_pool_allocator always simply double the next block's size ad infinitum! The pool class does offer methods to inquire and set the next_size property, but unfortunately, the singleton_pool underlying fast_pool_allocator is not accessible through the allocator interface!

After a certain point it may actually be less efficient to double it, as address space fragmentation will cause the OS to search harder for a continuous block. This may not be the reason pool does this, of course, but it's just a thought.

Is there a recommended way to set or limit next_size for pool allocators?

I have found a workaround to achieve this (see below) but am not very comfortable doing it this way.

2. I am under the impression fast_pool_allocator heavily leaks memory! As far as I can tell, it works properly in the beginning, but uses up to 7 times the memory a std::list

There is a bug in pool that causes it to severely leak memory if sizeof(T) is not aligned on bounds of at least sizeof(void*). This could be the reason. -- Cory Nelson