Re: [boost] Interprocess regexes

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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