Ion Gaztañaga wrote:
Thorsten Ottosen wrote:
What do we need to do to make a container that support the special allocators?
[...] Joaquín has successfully changed multiindex code to support Interprocess so maybe he knows better than anyone what's the best way to make an existing container compatible with Interprocess.
My adaptation process allows for special allocators to have the following relaxations with respect to the standard (which implicitly includes allocators from Boost.Interprocess): "For every type T, the type Allocator::rebind<T>::other::pointer can be any kind of Random Access Iterator, provided that it is explicitly constructible from the literal 0 (standing here as the null pointer) or from any p of type T* pointing into an area allocated by some instance of Allocator or some other allocator type rebound from Allocator. A pointer constructed from p shall dereference to *p." The former allows us to apply the following idiom: Allocator::rebind<T>::other::pointer p1=...; T* p2=&*p1; p2 and p1 point to the same T object and in general are interchangeable (I can construct an Allocator::rebind<T>::other::pointer from a T*). This leads to a particularly simple rule when adapting a container to these special allocators: Replace a T* p with a Allocator::rebind<T>::other::pointer *only if* p is a non-local variable. Otherwise (i.e. p is a local or automatic variable) just leave it like that and use the p2=&*p1 idiom if necessary. The rationale is that local pointers won't ever live in shared memory so it's not necessary to have them replaced by special pointes. This makes the adaptation process a little simpler. This process can be summarized as: 1. Replace (for adaptation purposes) your good old standard allocator with a special allocator such as that in https://svn.boost.org/trac/boost/browser/trunk/libs/multi_index/test/non_std... This will result in lots of compilation errors. 2. Look for all persistent (non-local) variables of type T* and re-type to Allocator::rebind<T>::other::pointer. This will result in further compilation errors due to the impedance between Allocator::rebind<T>::other::pointer's and the remaining T *'s. 3. Locate the points of impedance mismatch referred to above and adapt using the p2=&*p1 idiom. The whole process for Boost.MultiIndex is contained at the changeset: https://svn.boost.org/trac/boost/changeset/39922/ Alas the changeset includes other modifications not related to this, but I think it can give you an idea. Hope this helps a little. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo -- View this message in context: http://www.nabble.com/-interprocess--preparing-containers-tp20794468p2080277... Sent from the Boost - Dev mailing list archive at Nabble.com.