December 2009 - Boost - lists.preview.boost.org

[rdb, fusion, profile_templates] 0.2.03 - compilation speedup
by Jean-Louis Leroy 06 Dec '09

06 Dec '09

I have uploaded version 0.2.03 to the vault. No new features this time but improvements in compilation speed. The test_odbc project took more than 4.5 minutes to build in debug mode (msvc9, ThinkPad x200s, Intel L9400 with 2 cores @ 1.86 Ghz, 4 Gb RAM) and...17 minutes on a 2Gb RAM computer ! This was becoming unbearable. After a run through profile_templates - thanks to Steven Watanabe for creating this tool ! - I replaced the fusion::maps that were used to gather clause information in sql statement templates with a simpler, less flexible, less orthogonal and less capable version of my own. The result was a 41% speedup (calculated as (old-new)/old) on the 4 Gb computer and 85% on the 2Gb one. The number of template instantiations, as reported by profile_templates, dropped from 86330 to 62771. If someone is interested I can post the complete profiling reports. I plan to focus on datetime support now... Jean-Louis

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Re: [boost] [msm] Review
by Christophe Henry 06 Dec '09

06 Dec '09

Hi David, >>> 2. In Statechart, the definition of a state is coupled to the machine in which it resides >>> while in MSM the state can be defined totally in isolation of the machine, and, thus, reused in other machines >>> 3. In Statechart, the transitions are coupled to the from-state, and defined therein, >>> whereas in MSM, the transitions are coupled to the machine itself; this makes it a bit tricky to reuse a state in Statechart >> >> This is an important interface difference, isn't it? > Yes, which is why I brought it up; see (*) below. Thanks for doing it, I see this as an important point. >* - Yes and no... As I explained in my note to Dave, I did not mean API when I wrote that dreaded sentence about the interface similarity, >I meant it in a more abstract sense. BUT, for simple cases, where we do not deal with transition guards or nested machines, >there actually is a quite close similarity even at a syntactical level. Agreed. But isn't the interface similarity mainly due to the very tightly specified problem domain and to the fact that we all use the excellent MPL tool? Of course, simple state machines using MPL will all look slightly the same, as will do those based on OO-principles with each other. When a new implementation (even based on the same tools) brings important advantages, shouldn't it be considered for inclusion? >They treat guards differently. Yes. I'll come back to it in a minute. >> Let's now add a conflicting transition, which means another possible >> transition on the same event and the same source state, with guards >> deciding which (if any) transition will be taken. >We are now arguably leaving theoretical FSM's and entering pragmatic machines :-) Sure. Theoretical FSM's are anyway about the same for all. My point is to show that differences between MSM and Statechart are subtle but play an important role. >> With MSM you'd have, for example: >> typedef mpl::vector< >> row<State1, Event, State2, &Machine_::action, &Machine_::some_condition>, >> row<State1, Event, State3, &Machine_::action, >> &Machine_::some_other_condition> >> > transition_table; >> >> Could you now write the Statechart version for us? > No ;-) Then, I'm not an expert with Statechart but allow me to try to help ;-) I think (please correct me if I'm wrong) it'd look about like: sc::result react(const Event& evt) { if (some_other_condition(evt)) { action(evt); return transit<State3>();} else if (some_condition(evt) { action(evt); return transit<State2>();} } And this is one important difference, not just a syntactic one. With SC, the structure of the state machine is hidden in the code, which will make your conversion tool harder to write on the direction SC->MSM as the tool will not just be able to parse the code but also understand it. Add a few more actions or other piece of code and I wish your tool luck ;-) OTOH you get more flexibility. So, my point is, there are more differences that syntactic ones, as long as you make more complicated machines. I still agree with you on the point that interfaces are not "widly different" but I put this on the account of a clearly specified problem domain and the fact that most of Boost uses the same MPL tool (due its huge power. Thanks Dave, thanks Aleksey ;-) ). >Yes, there are syntactical differences and decouplings of state vs machine which makes MSM a nicer tool; >and, didi I mention that MSM is in my simple test cases six times faster? You did and I thank you for adding your own tests to the review. As an extra note, if you are ready to give up some state features and need just an enum for the states, you might want to take the FSM in the MPL book. It would probably even be possible to make from it a backend which could at some point partly support the different MSM front-ends. MSM does not yet support this solution in order to deliver a back-end supporting the state features specified by UML (again the restricted problem domain) but it is one of the backends I consider for addition. Do we agree to leave the dreaded sentence behind us and replace it with one saying that both libraries solve the same problem using a wildly different implementation with similarities in the syntax? Christophe

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[chrono] type_traits/common_type and integer/ratio
by Vicente Botet Escriba 06 Dec '09

06 Dec '09

Hi, I'm looking on how to continue with the Boost.Chrono library and I would like to know if * Boost.TypeTraits could take care of the common_type class template. * Boost.Integer could take care of the ratio class template. In this way Boost.Chrono will contain only the time related facilities, duration, time_point and Clocks. In order to minimize the task and been able to purpose as soon as possible the library for review I would like to concentrate on the implementation of the standard proposal and let for a future release the facilities Beman added as * Class template timer, with typedefs: * `system_timer` * `monotonic_timer` * `high_resolution_timer` * Process clocks and timers: * `process_clock`, capturing real, user-CPU, and system-CPU times. * `process_timer`, capturing elapsed real, user-CPU, and system-CPU times. * `run_timer`, convenient reporting of process_timer results. What do you think about this approach? Best, Vicente -- View this message in context: http://old.nabble.com/-chrono--type_traits-common_type-and-integer-ratio-tp… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Re: [boost] [msm] Review
by Christophe Henry 06 Dec '09

06 Dec '09

>> Repeating: the MSM/Statechart overlap in features and interface is quite >> unique to Boost. > > > They definitely overlap in features and also in intent, but my understanding > is that the interfaces are vastly different, and that's an important > distinguishing feature. Am I missing something? No you aren't. At first look, they seem similar, but as soon as you concretely start writing a state machine with both libraries, like Juraj could tell you (he did it), you'll start seeing that the differences are there. Of course, both use states, events and transitions but that's about all. MSM bases itself on the transition table, while with Statechart, the user writes his decisions in the react function. Composites are full state machines with MSM, a simple state with Statechart. MSM uses more metaprogramming, Statechart follows a solution with multiple translation units. Etc. etc. The point is, the interfaces differ, the normal usage even more and the "correct" way to use each (in the authors' eyes) much more as both follow a completely different philosophy, as many heated discussions showed. Christophe

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arithmetic meta functions and traits
by Zachary Turner 06 Dec '09

06 Dec '09

Is there any use for something like this? Following compiles on MSVC 9.0. Despite the simplicity of the final template, it was *NOT* easy to get this working given that there's about 10 ways you should be able to do this according to the standard, but poor SFINAE support makes it next to impossible to get your compiler to accept anything. Since it doesn't do anything highly fancy, I would wager it works on GCC and other compilers as well, although it needs to be tested. struct no_type { }; #define MAKE_BINOP_METAFUNCTIONS(op, binop, traits) \ template<typename T, typename U> no_type operator op (T, U); \ template<typename T, typename U> \ struct traits \ { \ typedef BOOST_TYPEOF(T() op U()) type; \ }; \ template<typename T, typename U> \ struct binop \ { \ private: \ typedef typename traits<T,U>::type result_type; \ public: \ static const bool value = !boost::is_same<result_type,no_type>::value; \ }; MAKE_BINOP_METAFUNCTIONS(+, is_addable, addition_traits); MAKE_BINOP_METAFUNCTIONS(-, is_subtractable, subtraction_traits); MAKE_BINOP_METAFUNCTIONS(/, is_dividable, division_traits); MAKE_BINOP_METAFUNCTIONS(*, is_multipliable, multiplication_traits); Obviously you can define other operators similarly, as well as unary operators. Zach

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Re: [boost] [explore] Library Proposal: Container Streaming
by Brian Wood 06 Dec '09

06 Dec '09

Jeff Flinn writes: > Regardless of the approach taken, I think this would be a useful > facility. I've created a similar, albeit much simplified facility for > two separate projects in the last 5 years. There've been several more > projects that could have used the more general facilities that this lib > offers. I think an on line approach is helpful and we have a service that writes Print functions based on user input -- http://webebenezer.net/cgi-bin/enrobo.cgi. This input: (list<int>) results in this output: void Print(std::ostream& so, const list<int>& abt1) { int indentation = 0; so.fill(' '); so << "\nabt1: "; so << "list has " << abt1.size() << "\n"; indentation += 2; list<int >::const_iterator mediator1 = abt1.begin(); list<int >::const_iterator omega1 = abt1.end(); for (; mediator1 != omega1; ++mediator1) { so.width(indentation); so << " "; so << (*mediator1); so << "\n"; } indentation -= 2; so << std::flush; } Brian Wood http://www.webEbenezer.net <http://www.webebenezer.net/> "The Kingdom of Heaven is like a treasure hidden in the field, which a man found and hid again; and from joy over it he goes and sells all that he has and buys that field."

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MSM Review period extended to Dec 13th
by David Abrahams 06 Dec '09

06 Dec '09

Hi All, We thought this might happen because of the Thanksgiving holiday, and it did: we are extending the review period for the Meta State Machine library until Dec 13th. However, please don't let that delay your review; we'd like to see them all as soon as possible. Msm was written by Christophe Henry, inspired in part by the example in the book "C++ Template Metaprogramming" (http://boostpro.com/mplbook) About the library: Msm (Meta State Machine) is a library allowing the user to easily define high-performance, straightforward and readable UML2 finite state machines, while respecting the principles of efficiency and declarativeness of the original example. To that end, Msm offers several Domain-Specific Embedded Languages that strive to closely emulate a standard UML diagram. Msm supports a broad range of UML features: - state entry/exit - transition actions/guards - composite states - history - orthogonal regions - terminate states - deferred events - explicit entry/fork - entry/exit pseudostates - anonymous transitions - transition conflicts And several non-standard features to make the developer's life easier (interrupt states, query about the current state(s)). Msm (in its current version, 2.0) can be found: * in the sandbox (http://svn.boost.org/svn/boost/sandbox/msm/) * or in the vault: (http://www.boostpro.com/vault/index.php?directory=Msm) Everybody on this list is invited to participate in this formal review. I hope to see your review of Msm, including your vote on acceptance, and I welcome your participation in the ensuing discussions on the Boost developers' mailing list. Please always include in your review a vote as to whether the library should be accepted into Boost. Additionally please consider giving feedback on the following general topics: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? - With what compiler? - Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? -- David Abrahams BoostPro Computing http://boostpro.com

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Regex allocator support
by Fred Sundvik 06 Dec '09

06 Dec '09

Hi, 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. This was quite straightforward to do, the allocators just had to be passed forward to the all internal classes it uses. The shared_ptr's had to be changed to use the three parameter constructor, that takes a a deleter and allocator, to prevent them from allocating. 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 figured out, that we can use a custom allocator as default, instead of std::allocator. That custom allocator then had to be specialized for the 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 the 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 that is BOOST_REGEX_BLOCKSIZE big. 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. So my question is, what are the chances that theese kinds of modificiations gets implemented in the actual library, and possibly in 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 this a quite big thing. Obviously we are doing well with the modifications we made here internally, but there are other applications too that would benefit, many embedded applications for example. Would our code changes be of any use? The changes are only the minimal needed to make it work in our case, and there's many compiler and option permutations not taken care of, so obviously a lot of work would still be needed. Also there's no additional unit tests made. Fred Sundvik Bugbear Entertainment Ltd.

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Notice: Boost.Atomic (atomic operations library)
by Helge Bahmann 05 Dec '09

05 Dec '09

Hello, as promised I have started extracting an atomic operations library. Current state is available at: http://www.chaoticmind.net/~hcb/projcets/boost.atomic It implements boost::atomic<TYPE> which faithfully mimics std::atomic<TYPE> as specified in the C++0x draft standard. As allowed by the standard, operations transparently fall back to locking when the underlying architecture does not support the requested operation, so the library already contains a "fallback" implementation that works an all platforms (using mutex from boost::thread). It currently natively supports gcc/x86, gcc/powerpc and gcc/alpha (I can vouch for the correctness of the implementations on these targets). It contains some entirely untested support for building implementations from CAS operations on other systems (e.g. _InterlockedCompareExchange on win), so I would greatly appreciate any feedback if it works/doesn't on any particular platform. There is some preliminary documentation, but not in boostdoc format -- after unsuccessfully struggling with bjam/boostbook & friends for a few hours I simply gave up and reverted to trusty old doxygen :( Is there any step-by-step guide on how to create, build and document a new library? I could really use that as the boost build and documentation system is pretty alien to an autotools-accustomed guy like me. Best regards Helge

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Re: [boost] [msm] Review
by Christophe Henry 05 Dec '09

05 Dec '09

Hi David, > It is sad that my comments are construed as criticism of MSM, since they merely point out the (I thought obvious...) >similarities with another library already in Boost. >After having tried MSM for a few days, most of it rocks, and I will provide a review later today. Oh I didn't take it as a criticism of MSM at all, merely of a valid issue which will have to be solved in Boost at some point because, as Boost grows, it is bound to happen again. I'll look at your review with great interest and thank you for taking the time to write it. To the core of your point, which is actually a valid concern. I agree that MSM and Statechart are solving the same problem. To explain what I (and probably Andreas) mean, let's look at the problem from a different angle. Let's suppose we'd build a Statechart 2.0. How would it look like? Would it go for the MSM way, putting as much as possible on the compiler, at the risk of breaking it, or the Statechart way, less metaprogramming and easier on compilers but slowlier and with a less descriptive interface (in my opinion)? Would it go for a transition table way or a state::react way? What kind of state storage would it take? And so on and so on. What is likely is that we'd probably not even manage to agree on the goals, much less on the design or the implementation. MSM comes from my frustration with not managing to make Satechart do what I needed. This shows that the philosophy of both authors is quite different and likely incompatible. Christophe

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Fixed bug in filesystem library ?
by Luca Severini 05 Dec '09

05 Dec '09

Hello everyone, I'm a newbie to boost libraries but I have some good experience in software development on Mac OS. Today I use downloaded and used boost for the first time. I use a MacBook Pro with Snow Leopard 10.6.2. The IDE is Xcode 3.2.1 Writing some very basic code to learn how to use the filesystem library I got assertions (below) simply iterating recursilvely through a local directory to list its content. /Developer/Test/TestFolder Boost_Test(57690) malloc: *** error for object 0xe518: pointer being freed was not allocated *** set a breakpoint in malloc_error_break to debug Investigating in the code I've found the assertions were triggered by two uninitialized std::string variables with same name passed to the functions detail::dir_itr_first() and detail::dir_itr_increment(). Initializing both to the simple content ".", directly in the constructor, seems to have fixed the problem (no assertions anymore). Here are the two functions I've changed in the file operations.hpp. The code I added is in green. Nothing has been deleted. I was thinking to follow the instructions to submit the fix but, please excuse me, I've found easier to send an email to the list. Hopefully someone with better knowledge of boost than me will submit gthe fix if it's the case o will find a better solution. Best regards, Luac Severini template<class Path> system::error_code basic_directory_iterator<Path>::m_init(const Path & dir_path) { if ( dir_path.empty() ) { m_imp.reset(); return detail::not_found_error(); } typename Path::external_string_type name("."); // String initialized to avoid assertion file_status fs, symlink_fs; system::error_code ec( detail::dir_itr_first( m_imp->m_handle, #if defined(BOOST_POSIX_API) m_imp->m_buffer, #endif dir_path.external_directory_string(), name, fs, symlink_fs ) ); if ( ec ) { m_imp.reset(); return ec; } if ( m_imp->m_handle == 0 ) m_imp.reset(); // eof, so make end iterator else // not eof { m_imp->m_directory_entry.assign( dir_path / Path::traits_type::to_internal( name ), fs, symlink_fs ); if ( name[0] == dot<Path>::value // dot or dot-dot && (name.size() == 1 || (name[1] == dot<Path>::value && name.size() == 2)) ) { increment(); } } return boost::system::error_code(); } template<class Path> void basic_directory_iterator<Path>::increment() { BOOST_ASSERT( m_imp.get() && "attempt to increment end iterator" ); BOOST_ASSERT( m_imp->m_handle != 0 && "internal program error" ); typename Path::external_string_type name("."); // String initialized to avoid assertion file_status fs, symlink_fs; system::error_code ec; for (;;) { ec = detail::dir_itr_increment( m_imp->m_handle, #if defined(BOOST_POSIX_API) m_imp->m_buffer, #endif name, fs, symlink_fs ); if ( ec ) { boost::throw_exception( basic_filesystem_error<Path>( "boost::filesystem::basic_directory_iterator increment", m_imp->m_directory_entry.path().parent_path(), ec ) ); } if ( m_imp->m_handle == 0 ) { m_imp.reset(); return; } // eof, make end if ( !(name[0] == dot<Path>::value // !(dot or dot-dot) && (name.size() == 1 || (name[1] == dot<Path>::value && name.size() == 2))) ) { m_imp->m_directory_entry.replace_filename( Path::traits_type::to_internal( name ), fs, symlink_fs ); return; } } }

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[iostreams] 1.41 gzip filter regression
by Alexander Arhipenko 05 Dec '09

05 Dec '09

Hi guys, In 1.41 we are experiencing regression in boost::iostreams::gzip_decompressor. Almost 50% percents of our test *.gz files failed to decompress. Following code snippet usually throws gzip error: std::ifstream f(n, std::ios_base::in | std::ios_base::binary); if(!f) { std::cerr<<"cant' open "<<n<<'\n'; } namespace io = boost::iostreams; io::filtering_istream in; in.push(io::gzip_decompressor() ); in.push(f); std::istreambuf_iterator<char> b(in); std::istreambuf_iterator<char> e; std::cout<<n<<'\n'; std::copy(b, e, std::ostream_iterator<char>(std::cout) ); Maybe that is caused by incorrect api usage. In this case, sorry for the noise in advance. I've attached minimal example that reproduces the issue. Build showfile executable and run ./showfile myfile.odt.bz2.gz > result. You should have 'error: gzip error' on stderr. Regards

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svn mergeinfo broken at the root.
by Steven Watanabe 05 Dec '09

05 Dec '09

AMDG Beman, I'm not quire sure what you did, but svn:mergeinfo doesn't work for me anymore. https://svn.boost.org/trac/boost/changeset/57638 destroyed the svn:mergeinfo for all the revisions that I had already merged (I have been doing all merges at the root). In Christ, Steven Watanabe

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symbolic links while building boost
by Zachary Turner 04 Dec '09

04 Dec '09

I use Windows primarily, and typically after building boost, there are two copies of each library. One with the version extension such as -1_41, and the other without. My understanding is that the one without the version number is supposed to be a symlink to the one with the version number on platforms such as linux, but that on Windows it is just a copy of the file due to poor support for symlinks in windows. My question is whether there has been any talk of changing this. Windows has supported first class symlinks since Vista, so it would seem possible to have Vista and beyond actually use this functionality and create real symlinks. Thoughts? Zach

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Re: [boost] Meta State Machine library review / MSM, question
by Christophe Henry 04 Dec '09

04 Dec '09

Hi Barend, >All my states are structs. Why is the state an integer here? How can I >(humanly or with MSM) translate that state to one of the states defined? >It works, I get a message, but still don't know which transition was not >provided... Unfortunately, no_transition is one of the few cases, where because of implementation details, MSM already crossed the compile-time / run-time boundary and all it has is the state id. Annex A shows the order in which the (usually hidden) state index is calculated. It's simply the order of appearance in the transition table. First are source states checked, then target states. Regards, Christophe

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Re: [boost] [msm] Review
by Christophe Henry 04 Dec '09

04 Dec '09

Hi all, Looks like there was a fair bit of discussion ;-) I'll try to give my take on the many discussed points. Jeffrey Bosboom wrote: >But I think this concern can be addressed if there is a documentation >page that compares the libraries that is included in (or linked from) >both libraries' documentation. This would make it much easier for a >user to choose one or the other without having to read the full >documentation for each. This sounds like a good idea to me. Not everybody followed the review. Andrew Venikov wrote: >I think an even better example would be map and hash_map. >They serve almost identical purpose but using totally different >techniques. The user of stl is expected to understand the differences >and chose the appropriate container. >Why not do the same with SC and MSM? Yes, we should really write a page explaining the trade-offs. David Bergman wrote: > I would even have welcomed some macros that introduce the state declarations for simplistic states, > from that transition table expression. There is something like this in eUML (on compilers with native typeof). Is this ok for you? typedef BOOST_TYPEOF(build_state( )) Paused; I can of course also add a macro for other compilers. David Bergman wrote: >Well, well, I seem to be the only one caring about this, and MSM sure is a fine library, >so I say 'welcome metamagical states!'. > NOTE: no, this was not a formal review ;-) I would welcome a formal review though. It'd help the review manager make a decision ;-) Jeffrey Bosboom wrote: >Decide whether MSM should be included or not on its own merits. If so, >then MSM makes Boost better; we shouldn't be so concerned with being >perfect that we lose the opportunity to be better. I agree. We should always decide on a library's merit and then see how to handle it. It'd be sad to lose an opprtunity to make boost more valuable on organisatory grounds. This doesn't apply only to MSM. David Bergman wrote: >You have a good point there. Although I would rather have seen the MSM guys collaborate with the Statechart guys >on making Statechart easier to use (especially the expression of the transition table) and/or more performant, though. >If that would have led to a combined Statechart 2.0 (analogous to Spirit 2.0) in a year, I would wait. Merging would be quite hard. While both libraries seem to have almost the same interface, scratching the surface will show many differences. The reason is that both libraries follow a pretty different philosophy and use different techniques. The best which might be achieveable would be a new front-end in MSM trying to match as much as possible SC's front-end. It would probably work for simple state machines. It might even work for composites. I'm not expert enough in Statechart to tell if more is possible. And the question is if someone would ever need this. You would still get the compiler limitations (and maybe add some more due to the added metaprogramming) and not all of SC's features. Why to use it then? However, if someone is willing to take this task on, I'd be ready to help. Ideally we would have to do the same in Statechart for one of MSM's front-ends. Sounds like a lot of work. Christophe

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Re: [boost] Meta State Machine library review starts Monday
by Christophe Henry 04 Dec '09

04 Dec '09

Hi Barend, > First I thought (intuitively) that the eUML was meant for output, but > apparently that is not the case, it is an embedded language for defining > state machines, right Right. It is at the same time syntactic sugar and a way to concentrate more information in the transition table. For designers, it is sometimes helpful to be able to see the whole transition at the same time and in the same place. > Is is somehow possible to export an MSM to a Boost.Graph, either within > the library, or in an example or separate utility headerfile? Yes it is. A transition table is relatively easy to parse and thus it should be possible to generate a diagram from a transition table. As shown at the last BoostCon, I'm working on a tool doing just this, but a graph export might be a nice and useful addition. Regards, Christophe

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[iostreams] input_sequence() questions
by Rob Riggs 04 Dec '09

04 Dec '09

I am attempting to adapt a windowed mmap reader, one which manages its mapping window using iterators, to a boost::iostreams direct source. I wrote this for reading large files via mmap on 32-bit platforms. The documentation shows that input_sequence() returns a pair of char pointers, not iterators. Is that really true or am I misreading the docs? http://www.boost.org/doc/libs/1_41_0/libs/iostreams/doc/concepts/source.html And it also shows that the input_sequence pointers are non-const. Why is that required for sources? Thanks, Rob

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[explore] Extending namespace std
by Jeffrey Faust 04 Dec '09

04 Dec '09

The various threads of discussion have died down. These include the name of the library, whether it's useful or not, if it is useful can it be satisfied by an existing library, whether it should it be part of another library or be a library on its own, and gcc compiler switches. All of these are important and we'll have to address them at some point (except perhaps the compiler switches). One item that was brought up and dismissed is that the implementation relies on extending namespace std. I'd like to visit this item more thoroughly. In my opinion the ideal interface is the most natural, simplest, and the most familiar to C++ developers: 'cout << c;' where c is a container of type C. Going beyond this nominal usage employs stream manipulators, again something that is known. Other forms such as 'print(c);' or 'wrapper(cout) << c;' are inferior interfaces. The former is clumsy and the latter does not extend in a natural way. Whether or not you agree, for the sake of argument, let's start with the statement that 'cout << c;' is the ideal interface for this library. Let's discuss how we can make this work. The only way I know how to make 'cout << c;' work for all cases is to put operator<<(C) in the same namespace as C. For example, variant<C, ...> will not stream if C is in std and operator<<(C) is not. The only way operator<<(variant) can see operator<<(C) is through ADL. If anybody can think of a mechanism where this will work without extending namespace std, please speak up. In regards to extending namespace std, I understand what the standard says and I think I understand the reasons behind it. I could add something to namespace std that conflicts with an existing item, changing the behavior. This is certainly undefined behavior, and the standard is right in restricting it. I don't believe this problem exist for the explore library. If we know that on all supported compilers that extending namespace std in this way behaves correctly, what is the concrete problem of doing so? Thanks for reading, -- Jeff Faust

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FunctionTypes broken in trunk
by Tor Brede Vekterli 03 Dec '09

03 Dec '09

Hi This is just a notice that the FunctionTypes library appears to have been broken since revision 56305, where several of the arity preprocessor files have become corrupted (more specifically, arbitrarily cut off) for some reason or another. The following extremely small test-case should fail to compile: #include <boost/function_types/function_pointer.hpp> int main() {} Best regards, Tor Brede Vekterli

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[msm] Comments
by Nelson, Erik - 2 03 Dec '09

03 Dec '09

I erroneously posted this on boost-users yesterday... Reposting it here today. I'm not competent to present a full review of the Boost MSM library, but I've been following it with interest since I discovered it at BoostCon. I've read very many mailing list exchanges between Christophe and users during this time. The MSM review hasn't generated a ton of traffic, and I'd like to contribute my comments for whatever they're worth. >What is your evaluation of the design? The Boost MSM library seems to be a well-designed implementation of state machine logic that is faithful to the UML standard in most areas and thoughtfully deviates from (or extends) it in a few places. >What is your evaluation of the implementation? I feel like the implementation is a clean example of modern C++ and abstracts state machine concepts quite well. The transition table in particular is implemented elegantly. >What is your evaluation of the documentation? Adequate >What is your evaluation of the potential usefulness of the library? Very useful... I expect to need this library for my work within the next 3-6 months >Did you try to use the library? I have not used the library. >How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? Something more than a quick reading, yet well short of an in-depth study. >Are you knowledgeable about the problem domain? Not particularly.. I've handwritten small state machines for GUI programming in the past As an additional comment, I believe Christophe himself typifies the best things about Boost. He has tirelessly worked on MSM and has been very supportive of users, incorporating many suggestions for improvement. MSM should definitely be included in Boost. Thanks Erik

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[explore] Library Proposal: Container Streaming
by Jeffrey Faust 03 Dec '09

03 Dec '09

Jared McIntyre, Danny Havenith, and myself, with support from Jeff Garland have developed a library to stream standard containers to output streams. We would like to submit this for review. The requirements for this library were gathered at the BoostCon 2007 Library in a Week sessions. An initial review was held and further requirements were gathered at BoostCon 2008. Everything can be found in the boost vault <http://www.boostpro.com/vault/> . Here is a direct link to explore.zip <http://www.boostpro.com/vault/index.php?action=downloadfile&filename=ex plore.zip&directory=&> . Some quick examples: #include <boost/explore.hpp> # include ... // simple vector example std::vector<int> vi; vi.push_back(1); vi.push_back(2); vi.push_back(3); std::cout << vi; // prints [1, 2, 3] // lets do some containers in containers std::vector<std::vector<int> > vvi; vvi.push_back(vi); vvi.push_back(vi); std::cout << vvi; // prints [[1, 2, 3], [1, 2, 3]] // associative containers std::map<std::string, int> si_map; si_map["hello"] = 1; si_map["world"] = 2; std::cout << si_map; // prints [hello:1, world:2] // containers of complex types std::list<date> dl; // date from boost::gregorian dl.push_back(date(2007, Jan, 1)); dl.push_back(date(2007, Jan, 3)); std::cout << dl; // prints [2007-Jan-1, 2007-Jan-3] // how about some boost container types: boost::array<std::string, 2> sa2; sa2[0] = "one"; sa2[1] = "two"; std::cout << sa2; // prints [one, two] Jeffrey Faust

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[serialization] polymorphic archives runtime failure (was: polymorphic archives ... generates linker errors)
by Christoph Heindl 03 Dec '09

03 Dec '09

Hi, thanks to Roberts help I managed to get the polymorphic archives issue, discussed earlier at http://article.gmane.org/gmane.comp.lib.boost.devel/196984) resolved. However there remains a runtime issue I can't resolve: Based on demo_polymorphic.cpp I've re-created minimal test example, which I think is correct, that fails with the runtime assertion it != m_map.end(), file libs\serialization\src\basic_serializer_map.cpp, line 72 on load. The demo consists of 5 files that create the following scenario: class B inherits from polymorphic base class A. An object of B is allocated on the heap and serialized through a base pointer A using a polymorphic xml archive. Saving runs without problems. Next, B is loaded from the stream through a base pointer to A. This fails with the mentioned assertion. What makes me wonder is that changing the from polymorphic_xml_iarchive to xml_iarchive and from polymorphic_xml_oarchive to xml_oarchive will not produce the named assertion. As mentioned in my previous post, I tested this with boost 1.40.0 and msvc 9.0. I would be really, really, grateful if you could give the demo a try. I've prepared everything so that it is just a matter of copying the files to libs/serialization/example and adding [ demo_bsl_run demo_polymorphic_cheind : cheind_a cheind_b ] The files can be found attached to my lost post at http://article.gmane.org/gmane.comp.lib.boost.devel/197061 Best regards, Christoph

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Re: [boost] Regex allocator support
by Fred Sundvik 03 Dec '09

03 Dec '09

Sorry for the previous message. Somehow I managed to send the message without a reply. A proper reply will follow soon. "Fred Sundvik" <fred.sundvik(a)bugbear.fi> wrote in message news:14525.2590220936$1259836768@news.gmane.org... >>> 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. >>> >> <snip> >>> >>> So my question is, what are the chances that theese kinds of >>> modificiations gets implemented in the actual library, and possibly > in >>> 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 > 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? > > 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: > >>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 > figured >>out, that we can use a custom allocator as default, instead of >>std::allocator. That custom allocator then had to be specialized for > the >>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 > the >>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 > 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 > > _______________________________________________ > Unsubscribe & other changes: > http://lists.boost.org/mailman/listinfo.cgi/boost >

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Re: [boost] Regex allocator support
by Fred Sundvik 03 Dec '09

03 Dec '09

>> 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. >> > <snip> >> >> So my question is, what are the chances that theese kinds of >> modificiations gets implemented in the actual library, and possibly in >> 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 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? 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: >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 figured >out, that we can use a custom allocator as default, instead of >std::allocator. That custom allocator then had to be specialized for the >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 the >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 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

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