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Subject: Re: [boost] Interprocess regexes
From: Mike Spertus (mike_spertus_at_[hidden])
Date: 2009-12-05 23:43:14


Hi Phil,

Phil Endecott <spam_from_boost_dev <at> chezphil.org> writes:
>
> Hi Mike,
>
> Mike Spertus wrote:
> > basic_string and other containers take an
> > allocator template argument, while basic_regex does not.
> >
> > If basic_regex had an allocator it would reap all the same benefits that
> > other string and container types do. In particular, it would be possible
> > to use boost::interprocess to place them in shared memory.
>
> IIUC, while the custom allocators let you put std::containers in shared
> memory they are still not very useful since they can only be used by
> the process that put them there - other processes will (potentially)
> see the shared memory at a different address and all the pointers will
> be wrong. Is this level of functionality useful to you?
>
Custom allocators do let multiple processes use the same containers in shared
memory, even if they are mapped to different addresses because allocators define
a pointer type for the container to use internally. For example,
Boost::Interprocess provides an interprocess allocator that uses relative
pointers to handle the exact issue you describe. See
http://www.boost.org/doc/libs/1_41_0/doc/html/interprocess/allocators_containers.html#interprocess.allocators_containers.containers_explained
for details.

So shared memory STL containers are actually very useful, and we use them
extensively in our project to share fully STL-compatible data structures between
many processes. The failure to have an allocator in regexes is a big problem for
us because configurations (which is what we like to share) often include regular
expressions.

Mike
> Phil.
>
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