Re: [Boost-users] boost::pool

Subject: Re: [Boost-users] boost::pool
From: strasser_at_[hidden]
Date: 2009-11-03 13:07:11

Zitat von Frank Meerkoetter <frank_at_[hidden]>:

>> as is expected. you might want to look into using thread specific  
>> pools, that
>> only synchronize when a new pool block is allocated.
>
> could you please elaborate a bit on this? How would i do this with the
> std::allocator implemenation provided by Boost.Pool?

the basic idea is to have an object pool for each thread, so that only  
when the pool runs out of memory std::new is called and a mutex lock  
is required. thread-local allocations can run concurrently.

you could use boost.pool for this, if none of your threads ever  
deallocate an object that was allocated by another thread (and thus be  
part of another pool). you`d have to write your own allocator I think.
but boost.pool isn't suitable as a general purpose allocator anyway,  
because of O(n) free().

that`s another thing that Pool2 should support. some kind of  
hierarchial pool structure. when a pool runs out of memory it requests  
new memory from its parent pool, and also pools deallocations and puts  
those back into the right pool, so you don`t have the problem  
described above.

Zitat von Nigel Rantor <wiggly_at_[hidden]>:
>
> I would be really interested to hear more detailed critique of the  
> current pool library from people who know/have used it.
>

there`s nothing "wrong" with boost.pool in the sense that it has  
errors. but it only supports a very limited use case:
pools of objects of the same type that are used to allocate objects  
individually  but deallocated as a pool.

here is (an outdated version of) the code I currently use, with O(1)  
allocation and O(1) deallocation.
http://www.boostpro.com/vault/index.php?action=downloadfile&filename=intrusive_pool.hpp&directory=Memory&
(don`t use it, that version still had bugs)

but like boost.pool, it only supports a few (other) use cases, it is  
not a generic library.

here is an introduction to two allocation algorithms that pools could  
use to support arbitrary-sized objects:
http://www.boost.org/doc/libs/1_38_0/doc/html/interprocess/allocators_containers.html#interprocess.allocators_containers.memory_algorithms