Re: [boost] [context] implementation comments

Subject: Re: [boost] [context] implementation comments
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2011-03-05 06:00:46

On 04.03.2011, at 21:18, Oliver Kowalke wrote:

> Am 04.03.2011 20:06, schrieb Sebastian Redl:
>> On 04.03.2011, at 19:16, Oliver Kowalke wrote:
>>> Many of the stl container don't use their allocators - for instance std::list allocates its internal data structures with new (allocator can not applied) - therefore I believe it would not make sense to parametrize fiber with an allocator.
>> I don't know what std::list implementation you are referring to, but it's buggy. A standard container has to use its allocator for *all* allocations. That's what rebind is for.
>> 
> stl::set of gcc-4.4.5 does not use its allocator
> 
> C++ standard 23.2.1:
> '... are called only for the container’s element type, not for internal types used by the container. [ Note: This
> means, for example, that a node-based container might need to construct nodes containing aligned buffers
> and call construct to place the element into the buffer. — end note ]...'

That clause only applies to construct() and destruct(), not to memory allocations.
Here's the relevant citation, from C++0x 23.2.1p8:
"Unless otherwise specified, all containers defined in this clause obtain memory using an allocator. [...]
A copy of this allocator is used for any memory allocation performed, by these constructors and by all
member functions, during the lifetime of each container object or until the allocator is replaced."

If GCC's set uses plain new anywhere, it's broken. If it uses placement new to construct its internal structures, that's fine.

Sebastian