We recently had to use the regular expression library in conditions where there was no available physical memory, for reporting resource consumption when our console game runs out of memory. This wasn't possible however due to the fact that the basic_regex does some dynamic allocations and doesn't provide any allocator specialization, allthough match_results for example does. So we modified the boost code a little bit and added a new template paramter for the allocator, and made constructors that takes allocators as parameters.
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So my question is, what are the chances that theese kinds of modificiations gets implemented in the actual library, and possibly
the next c++ standard library as well? I consider it a quite big design flaw to not have any control of the internal allocations, so for me
in this
a quite big thing.
+1; I agree with the OP's sentiments, though I wouldn't say it's necessarily a "big" design flaw. However, I've never used the Boost.Regex library, and I don't know if the next standard specifies allocator parameters. I gather it doesn't?
The mem_block_cache system was a bit more complicated. Initially we disabled it completely, but that obviously wasn't the best solution. So we
out, that we can use a custom allocator as default, instead of std::allocator. That custom allocator then had to be specialized for
mem_block_nodes, and the funcion calls to get_mem_block replaced by allocator calls. Our implementation isn't ideal, though as we used mem_block_node as the specialization, and to pass the correct size to
allocator, we allocate BOOST_REGEX_BLOCKSIZE / sizeof(mem_block_node) of them, this way it works for allocators that don't specialize for mem_block_node(but only if the size is dividable by sizeof(mem_block_node) ). Better would probably be to make a new type
Sigh... no. The original regex++ library upon which the Boost version is derived *did* have allocators for everything. But during review folks felt quite strongly that: a) It was overkill. b) Regex should be free to manage it's own memory - it's not a container - it's needs are much more complex than that - so it should be free to optimize memory allocation and caching as it sees fit. As a result this facility was removed. Rightly or wrongly, no one on the stds committee questioned that design decision. Some specific comments on the other issues: figured the the that
is BOOST_REGEX_BLOCKSIZE big.
Can you not just define BOOST_REGEX_RECURSIVE and use the stack based implementation that does away with that altogether?
We also found another problem with allocation, the match_result::format functions only takes string_type, that isn't specialized by any allocator as they input. This made it impossible to call them with strings using different allocators. So we added specializations of those functions for different allocators and traits. There are probably more functions like that, but since our code doesn't use them there was no need to change anything.
The current Trunk allows any string, container or character type, plus function objects to be used as arguments to regex_format/regex_replace etc, which should avoid that problem.
We recently had to use the regular expression library in conditions where there was no available physical memory, for reporting resource consumption when our console game runs out of memory.
I'm not sure I understand the issue here, that operator new doesn't report out of memory conditions? What does your allocator do that's different to operator new, and why not replace global new and delete with calls to your custom allocator? Just trying to get a handle on the issue...
So my question is, what are the chances that these kinds of modifications gets implemented in the actual library, and possibly in the next c++ standard library as well?
As noted above, I was asked to remove this feature during review, so I'm not *that* keen to put it back in! As far as the standard is concerned it's basically a done deal at this stage in the process - too late for such a big change. WRT Boost I'd really like to get a handle on the issue better before making judgment - you seem to be one of very few people actually using custom allocators ;-) Regards, John. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost