March 2010 - Boost - lists.preview.boost.org

Re: [boost] [contract] Released Contract Programming Library on SourceForge
by Andrzej Krzemienski 21 Mar '10

21 Mar '10

> I have released on SourceForge a library that implements Contract > Programming (a.k.a. Design by Contract(TM) ) for C++. I am considering > to submit this library to Boost (as Boost.Contract). > Comments? Hi, Just another thought for a tiny extension that came to my mind. I tried to use the block invariant as a regular assert: int main() { CONTRACT_ASSERT_BLOCK_INVARIANT( fee fee fee ); } This code compiles and works fine. This is because "disabling block invariants" means that the entire macro invocation will disappear, inclusive of the nonsense I wrote inside. We are used to it because this is how C-style asserts work, but one of the advantage of asserts over comments, as it is often advertised, is that the predicates are checked for syntactic and (to some extent) semantic correctness. But this is not the case if we disable the assertion macros. I believe, it would be useful if "disabling block invariants" meant no run-time overhead, but still checking syntactic correctness. It would be possible if the macro CONTRACT_ASSERT_BLOCK_INVARIANT( expression ); were replaced with something like: ... sizeof( expression ) ... then, the expression is not evaluated, but required to be correct. If the value of sizeof is not used it should be eliminated by the compiler. Obviously, the same would be applicable for all the other types of checks, Regards, &rzej

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GSOC 2010 : Boost.graph
by Chinmaya Poswalia 21 Mar '10

21 Mar '10

In boost.graph what would be better : a) Manipulate the original graph - it would save space(crucial for big graph) -if the user want he can copy the graph object to a new object and then feed into functions b) Generate a new graph - although space will be allocated but user has the opportunity to directly input the graph.

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GSOC 2010
by Chinmaya Poswalia 21 Mar '10

21 Mar '10

Hello, I want to enquire following things? 1) Who are the mentors and can i get there email-address? I was not able to find there names on the project list site.

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[Boost.Locale] More updates
by Artyom 21 Mar '10

21 Mar '10

Hello, Updates ------- I had uploaded updated version of Boost.Locale that includes few bug fixes and some cleanup of MSVC warnings so now it clearly compiles with /W3 under MSVC. Also some documentation updated. Docs: http://cppcms.sourceforge.net/boost_locale/html/ Tutorial: http://cppcms.sourceforge.net/boost_locale/html/tutorial.html Download (boost_locale-svn_r1112.zip): https://sourceforge.net/projects/cppcms/files/ Formal Review Request --------------------- I want to submit the library for formal review: - When can it be done? - Do I have to provide full BJam build before formal review (at this point it builds fine with CMake)? - Do you think that I should wait more, improve the library more and if so what exactly? Best, Artyom

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[proto] call for help with msvc-7.1
by Eric Niebler 21 Mar '10

21 Mar '10

A recent check-in of mine (https://svn.boost.org/trac/boost/changeset/60706) broke proto on msvc-7.1. For instance, see <http://tinyurl.com/yg5wgw5>. I don't have access to this toolset anymore. Is there anybody out there willing to give this problem a shot? Or is it time to drop support for this old compiler? -- Eric Niebler BoostPro Computing http://www.boostpro.com

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[Log] Pre-review questions
by Christian Holmquist 21 Mar '10

21 Mar '10

Hi, I'm currently attempting to convert parts of our production log system to using Boost.Log as part of my review. At first glance this looked like a trivial thing, since Boost.Log supports all features (and more!) than I would need to do this task. However, I can't find what I'm looking for in the docs and I wish to not poke around anymore in the Boost.Log code. Simple task 1 I've two source level attributes, System and Severity. I wish to create a log macro that takes these two arguments. enum System { SYSTEM_A, SYSTEM_B, }; enum SeverityLevel // I don't want to use the built-in severity enum, since need flexibility to add/remove levels. { FREQUENT, DEBUG, TEMP, INFO, WARNING, ERROR, }; void foo() { LOG(SYSTEM_A, INFO, "Hello cruel world" << "!"); } The above is not a complicated scenario and I should be able to quickly find an answer. Maybe I've just missed it..:) Simple task 2 Create a custom filter without using any Lambda magic. struct Filter { System sys; SeverityLevel sev; bool operator()(???) { // pseudo-code, since I don't know how to write this return Attributes["System"] == sys && Attributes["SeverityLevel"] >= sev; } }; Help appreciated, I would like to get to the more complicated parts.. / Christian

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[gil] Can not open test.jpg
by Mariusz Kwiczala 20 Mar '10

20 Mar '10

Hi, I cannot open test.jpg from boost_1_42_0\libs\gil\example\test.jpg I use below application: InfranView FireFox IE Windows tools: (Paint, WLXPhotoGallery ... ) Does it mean that GIL uses some special, jpg file format? :) Best regards, Mariusz

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Heaps and Queues for GSoC
by Thomas Mullaly 20 Mar '10

20 Mar '10

Hello my name is Thomas Mullaly and I am currently an undergraduate in Kent State's Computer Science department. I'm interested in submitting a proposal for this years Google Summer of Code for the Heaps and Queues project, but, first I was wondering if somebody could explain what the requirements are for this project. So I have a better understanding of the project when I write a proposal. -Thomas Mullaly

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[SoC] Call for Mentors
by Andrew Sutton 20 Mar '10

20 Mar '10

All, Boost is once again participating in the Google Summer of Code program. I'm looking to establish an official list of possible mentors for student projects. I have a list of people that have already offered to mentor this year and people who I think might offer to mentor based on their past participation :) but I thought it would be a good idea to do this a little more officially. If you are interested in mentoring a student this year, please send your me your gmail id (e.g., andrew.n.sutton) and a short description of the kinds of projects you would be interested in mentoring. The gmail id is required for me to invite you to be a mentor, as far as I can tell. Please note that mentors should be prepared to work with one student throughout the course of the summer. This typically means reviewing the student's work on a weekly basis and providing guidance by answering questions and suggesting improvements on their work. Thanks, Andrew Sutton andrew.n.sutton(a)gmail.com

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GSOC 2010
by Augustus Q Odena 19 Mar '10

19 Mar '10

Hi, My name is Augustus Odena. I'm really interested in a few of the project ideas that Boost has listed for Google Summer of Code (Heaps and Queues, Bits and Ints, Graph Connectives and Topology Generators). It was suggested to me by the Hints Page that I should join the mailing list - so I've done that. I'd really appreciate it if, whenever someone had the time, they could perhaps fill me in a little bit more on the details behind those projects and their relative merits. I'd be happy to provide any sort of information about myself that would be helpful. -- Thanks, Augie Odena

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Range begin/end and Fusion begin/end
by Mathias Gaunard 19 Mar '10

19 Mar '10

In C++0x, begin and end are supposed to be found through ADL, and this might end up considering fusion::begin/fusion::end as possible overloads. Unfortunately, this breaks, as fusion::begin and fusion::end produce hard errors when passed something else than a fusion sequence. All in all, I find ADL very dangerous. Should it be advocated not to use the names "begin" and "end" for something else than ranges to avoid issues? I suppose that for Fusion, it could be possible to use SFINAE to mask the overloads if the arguments aren't fusion sequences.

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[log] Boost.Log formal review ongoing
by Vladimir Prus 19 Mar '10

19 Mar '10

Boosters, just a a friendly reminder that the formal review of the Boost.Log library, written by Andrey Semashev, is ongoing through March 17, 2010. There's still enough time to submit reviews and have them discussed, so please take a look at the library and share your thoughts. The documentation for the current version is available at: http://boost-log.sourceforge.net The downloads are at: http://sourceforge.net/projects/boost-log Here are the important points: 1. All comments are appreciated. Even if you don't have the time for in-depth study of everything, comments on parts of the library are welcome. In particular, if you are already using logging in your applications and have specialized requirements, you might want to directly check how the proposed library handles them. 2. The reviews and all comments should be submitted to the developers list, boost(a)lists.boost.org and the email should have "[log]" prefix in the subject to make sure it's not missed. The deadline for reviews is 23:59, March 17, PST = 2:59, March 18, EST = 7:59 March 18, GMT = 10:59, March 18 MSK 3. Please explicitly state in your review whether the library should be accepted. 4. The general review checklist is provided below: - 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? Thanks, Volodya

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[SoC] Summer of Code
by Andrew Sutton 18 Mar '10

18 Mar '10

All, Boost is once again participating in the Google Summer of Code program. If you are a student who is interested in contributing to Boost, now would be a good time to discuss your plans on the *developer's* mailing list ( http://lists.boost.org/mailman/listinfo.cgi/boost) Student applications will be accepted here starting March 29, and can be submitted here: http://socghop.appspot.com/. If you have any questions, please feel free to ask me directly or respond to this message. Cheers, Andrew Sutton andrew.n.sutton(a)gmail.com

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[log] Boost.Log formal review
by M-Square 18 Mar '10

18 Mar '10

> Please explicitly state in your review whether the library should be accepted. Yes, I think the library should be accepted. In my view, the library should not be reviewed with the objective of whether it contains all possible implementations that might desired in the world, but whether it’s design and implementation is flexible enough to adopt useful extensions, like binary logging or a printf-style interface. It is unreal to expect from a first implementation to be the mother of all logging libraries, i.e. contain all desired functionality at once. It should be judged on whether it can BECOME the mother of all logging libraries and in my opinion it is flexible enough to do so. In our project, described in last month's ACCU Overload 95 (http://accu.org/index.php/journals/1606) we required a powerful logging/tracing library, mainly for the higher levels of the application. Since our guideline is to use Boost functionality wherever suitable, we particularly looked at the Boost library to fill our needs. It seemed to fulfil our requirements quite well, so we decided to take it on-board. We integrated it into our software, and first experience is that it works quite well. However, in the light of this review I would pay attention to a few aspects that I came across: - complexity of the interface, and how to improve - few design/implementation aspects - high-performance requirements INTERFACE COMPLEXITY ===================== A number of reviewers have mentioned the complexity of the interface and the fact that this might discourage new users. I think introduction of trivial logging partly reduced this problem, but whenever you want to use the library in a more subtle way, you have to know a lot and you have to do a lot. When implementing the various sinks and backend flavours I too found my code blurred with heavy template and shared-pointer handling at a level where I didn't want to see it. Thinking about how to improve this, it seemed to me that the library was lacking an extra interface level between trivial logging and the low-level interface of sinks etc. This extra interface should hide complexity, but still allow the user full control over the detailed aspects of the logging components. In my view this extra-level interface could be well-solved with a policy-based design. The user should just be required to provide the policies for the various aspects (front-end, back-end, formatter, filters) as well as the necessary parameters (file name etc.). The actual assembly of the logging components should be done by the library internally. I put this idea into practice, and, although not an expert in this field, developed a few policy-based creator classes, as well as the most common policies that I could forsee. This made the library much easier to manage and my code look much better. Adopting this approach would greatly remove the objections against the highly complicated interface. Users can just use the policies provided, and if the ones provided do not fit a user's needs, he can easily copy an existing one and modify it according to his wishes. The current design of the library allows insertion of this extra interface level well, proving its flexibility. DESIGN/IMPLEMENTATION ASPECTS =============================== When using the library I came across a few design aspects that might need some improvement. 1. Missing some polymorphism I know it is cursing in the church, but at certain moments I could do with a bit smarter use of polymorphism. To give an example, when my application shuts down unexpectedly, I want to tell the sinks around to stop their work and dump their contents if necessary. For the moment, and as far as i know, I still have to make a distinction between synchronous and asynchronous sinks, as only the asynchronous sinks support these stop methods, and even then I have to take the particular kind of backend in consideration in order to approach them, as this stop method is attached to the backend-templated class. It would be better to lift these methods to a class higher in the hierarchy. There are a few other points in the design were this is the case as well. This being said, there might be good reasons for the current design that I cannot oversee, but then I’d like to see them mentioned in the documentation. 2. In some cases, you might want to be more in control of what the logging library is actually doing. When sending off messages to a sync or async sink, you are only partially in control. Therefor my idea would be to provide something like a buffering logger, that buffers the messages it receives, and only sends it off to the core when the user tells him to. HIGH-PERFORMANCE REQUIREMENTS ================================ In my view, one of the most important aspects to judge a logging library on is its performance. I haven't seen to much about it in the reviews, but I think it is one of the first thing to look at when comparing libraries. I haven't performed comparison tests in detail, but from the results published it looks like Boost.Log is still lagging a bit behind in the multi-threaded case. The question is whether there is room for improvement here. If not, you will definitely loose out on faster libraries. When looking at our current project, there are certain parts of the application where we need a real fast (i.e. low cost) logging facility, and that is something that the current library is not going to offer (nor any of the more common logging libraries around; too often I read comments like "we choose rlog because it is twice as fast as.. "). So my idea would be to develop a lightweight logging module, that can operate next to the current functionality, but is particularly suited for applications or parts of applications where high performance is an issue. This could also be the light and simple library that people are asking for. I think it would be great to have both under one hood, allowing the user to select the kind of performance vs. capability that he wants. This also takes away the burden on the current implementation of having to be both lightweight and feature-rich. For the rest of the formal review questions: >What is your evaluation of the design? The design covers a good set of requirements to start with. It seems to be quite flexible to cater for new functionality. As stated, it might be useful to ease the use of the highly templated interface to prevent it of becoming a hurdle for novices. >What is your evaluation of the implementation? Only looked partly to the implementation, especially with performance in mind. I'm convinced that the implementation is good in general, although improvements can be made, especially with performance in mind. Date/time formatting is still a candidate in this case. >What is your evaluation of the documentation? The level of documentation is sufficient but not more then that. It seems to be written from the view of the developer or from a highly-experienced user. It therefor makes it difficult for a novice to use the library quickly. The introduction of trivial logging however improved this situation. In my view it should be reworked somewhat to cover the questions of less knowledgeable users (i.e. more explanation, more illustration through examples or references to the examples in the code). >What is your evaluation of the potential usefulness of this library? I think the library is very usefull. Regarding covered functionality it is somewhat equal to other well-known logging libraries, and the design is well-suited for extension in all areas where more functionality is required. >Did you try to use the library? With what compiler? Did you have any problems? We tried the library with Microsoft Visual C++ 8.0. We didn’t find any problems with the compiler, apart from some issue with MFC. There is a problem linking Boost.Thread statically with MFC, but this is a problem that resides outside Boost.Log. >Are you knowledgeable about the problem domain? Yes, developed this kind of functionality in earlier days. -- View this message in context: http://old.nabble.com/-log--Boost.Log-formal-review-tp27940788p27940788.html Sent from the Boost - Dev mailing list archive at Nabble.com.

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[log] Boost.Log Formal Review
by sam.gundry＠gmail.com 18 Mar '10

18 Mar '10

(This is my first Boost library review so take it easy...) > Please explicitly state in your review whether the library should be accepted. Yes. There are some concerns but I think it is very nearly complete, as far as my usage is concerned. These concerns are elicited in detail below but for now my three major ones are: - __LINE__, __FILE__ as attributes - Boost.DateTime formatting is sloooowwww - Ability to strip/compile out log messages in their entirety > What is your evaluation of the design? I haven't applied it heavily yet but so far the design seems logical. Separating the sinks and sources provides good flexibility. I'm yet to delve into usage of the filters though. > What is your evaluation of the implementation? I can't speak for the correctness of the implementation, but from a performance perspective, I've compared it to log4cxx (see the sourceforge thread Andrey has referred to) and it is comparable and/or better in most of my usages. Given the flexibility, I am prepared to pay for a little performance hits. A concern, which again Andrey has mentioned during this review, is the speed of Boost.DateTime formatting. From our comparisons, it is about 3-5x slower than log4cxx. Is it possible to have a bare-minimum date time formatter similar to log4cxx's implemented? I wrote a quick little wrapper using a customised strftime (for microseconds) with the most basic caching (which log4cxx's formatter uses) and performance was comparable. > What is your evaluation of the documentation? For most the part, very good. Definitely sufficient/adequate for acceptance. The design and installation pages, etc, are extremely clear and easy to read. Personally, I would prefer a few more concrete examples. For example, (a minor one, I know) but how do you specify keywords via a settings file. > What is your evaluation of the potential usefulness of the library? High. An efficient, highly functional and configurable logging library has much potential. I've found __LINE__ and __FILE__ missing as attributes. Andrey advised these are part of named_scope but the formatting is currently missing. Ideally - and I don't know if this is technically possible but - I would prefer these as just another attribute. Instead of requiring a BOOST_LOG_FUNCTION() call when you want to use them, you should be able to specify it as per usual, something a long the lines of: backend->set_formatter( fmt::format(%1% [%2%:%3%] %4%) % fmt::attr< SeverityLevel >("Severity") % fmt::attr< fmt::scope::file >("File") % fmt::attr< fmt::scope::line >("SrcLineNumber") % fmt::message() ); And then BOOST_LOG_SEV(...) << " a message" has the file and line attribute values already. Note, no need for BOOST_LOG_FUNCTION. With respect to compiling out the log messages: it would be desirable for security, code protection and/or performance if the ability to specify certain log records to be stripped out of the source code. A hack such as follows - which is obviously extremely inflexible - allows the users to define LOG_NTRACE to compile out all trace messages: # if defined (LOG_NTRACE) # define LOG_TRACE(logger, stream) (void(0)) ; # else # define LOG_TRACE(logger, stream) BOOST_LOG_SEV(logger, trace) << stream; # endif Something a lot smarter and flexible built into the library is desirable. Say, templated on your custom severity levels (or, indeed, any arbitrary attribute) and generating disable/enable macros. > Did you try to use the library? With what compiler? Did you have any problems? Yes. gcc 4.3.3, msvc 9, and qcc/gcc 4.x.x (can't remember) on QNX. No problems. > How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? Initially, at the end of last year, I compared performance and functionality to log4cxx. However, for this review, I have had a quick read of the docs (not the code) and attempted integrating it for our purposes, about 4 hours worth. > Are you knowledgeable about the problem domain? Not hugely. Middle-of-the-road. Neither here nor there. 5/10. Relatively average. A big thanks to Andrey for all his effort. Good luck with the acceptance! Cheers, Sam

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[log] Boost.Log formal review is over
by Vladimir Prus 18 Mar '10

18 Mar '10

Boosters, The forward review of the Boost.Log library is now officially over. Big thanks to Andrey for a solid proposal, and for everybody who participated in review. I plan to announce review results in a week from now, on Mar 25. Thanks, Volodya

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[unordered] unordered_set::erase() complexity bug?
by Stefan Strasser 18 Mar '10

18 Mar '10

I think there is something very wrong with boost's implementation of unordered_set/map. 1 unordered_set<int> s; 2 for(int c=0;c<nr;++c) s.insert(c); 3 for(int c=nr-1;c>=0;--c) s.erase(s.find(c)); results: nr: time 20000: 0m0.244s 40000: 0m0.940s 60000: 0m5.584s 80000: 0m4.232s 100000: 0m34.814s 120000: 0m33.486s the function that's causing this is erase(), which is specified to be O(1) average, O(n) worst. I can't think of a reason why it should be O(n) in this case (perfect hash, erase doesn't rehash). but even if it was, the results should be at worst quadratic. load_factor() is below 1, bucket_count(x) is 1. if line 3 is changed to: 3 for(int c=0;c<nr;++c) s.erase(s.find(c)); 20000: 0m0.008s 40000: 0m0.016s 60000: 0m0.028s 80000: 0m0.032s 100000: 0m0.040s 120000: 0m0.044s as you would expect. even if I do the very same thing as above using Boost.Intrusive (using a load factor of 1), I get expected results: struct element : intrusive::unordered_set_base_hook<>{ ... for(int c=0;c<nr;++c) s.insert(*new element(c)); for(int c=nr-1;c>=0;--c) s.erase(s.find(element(c))); 20000 0m0.008s 40000 0m0.016s 60000 0m0.024s 80000 0m0.024s 100000 0m0.032s 120000 0m0.040s but surprisingly enough, the TR1 implementation shipped with libstdc++ also has a problem like that: 20000: 0m0.368s 40000: 0m1.448s 60000: 0m1.668s 80000: 0m7.160s 100000: 0m7.808s 120000: 0m13.349s am I missing something or is there really the same bug in 2 major implementations of unordered_set? it effectively caused a deadlock in some of my code. I'm using 1.38. no bug report in Trac.

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[date_time] memory leak?
by Bartosz Marcinkiewicz 18 Mar '10

18 Mar '10

Hello, Code: #include <iostream> #include <boost/date_time/posix_time/posix_time.hpp> int main() { std::cout << boost::posix_time::microsec_clock::local_time() << std::endl; return 0; } Running through valgrind yields this: ==5963== ==5963== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 7 from 2) ==5963== malloc/free: in use at exit: 1,595 bytes in 27 blocks. ==5963== malloc/free: 63 allocs, 36 frees, 7,878 bytes allocated. ==5963== For counts of detected errors, rerun with: -v ==5963== searching for pointers to 27 not-freed blocks. ==5963== checked 173,784 bytes. ==5963== ==5963== 619 bytes in 20 blocks are possibly lost in loss record 7 of 7 ==5963== at 0x4A06FFC: operator new(unsigned long) (vg_replace_malloc.c:230) ==5963== by 0x352C0A0140: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.12) ==5963== by 0x352C0A0D64: (within /usr/lib64/libstdc++.so.6.0.12) ==5963== by 0x352C0A0F01: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.12) ==5963== by 0x408AD7: boost::date_time::date_generator_formatter<boost::gregorian::date, char, std::ostreambuf_iterator<char, std::char_traits<char> > >::date_generator_formatter() (in /home/bma/c++/boost_dt) ==5963== by 0x407B20: boost::date_time::time_facet<boost::posix_time::ptime, char, std::ostreambuf_iterator<char, std::char_traits<char> > >::time_facet(unsigned long) (in /home/bma/c++/boost_dt) ==5963== by 0x40494B: std::basic_ostream<char, std::char_traits<char> >& boost::posix_time::operator<< <char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, boost::posix_time::ptime const&) (in /home/bma/c++/boost_dt) ==5963== by 0x402AA0: main (in /home/bma/c++/boost_dt) ==5963== ==5963== LEAK SUMMARY: ==5963== definitely lost: 0 bytes in 0 blocks. ==5963== possibly lost: 619 bytes in 20 blocks. ==5963== still reachable: 976 bytes in 7 blocks. ==5963== suppressed: 0 bytes in 0 blocks. ==5963== Reachable blocks (those to which a pointer was found) are not shown. ==5963== To see them, rerun with: --leak-check=full --show-reachable=yes This is boost-1.37.0-9.fc11 (fedora core 11), gcc 4.4.1, x86-64 platform. Is it memory leak? Best regards, bma. -- Bartosz Marcinkiewicz tel. (+48) 516 034 243 e-mail: bma(a)epcon.pl, bartosz.marcinkiewicz(a)epcon.pl EPCON Sp. z o.o. www.epcon.pl adres: 53-407 Wrocław, ul. Gajowicka 114/116 tel. (+48) 71 361 75 55 ext.36 fax (+48) 71 361 74 44 NIP PL 899-24-92-498 KRS 0000190187 REGON 932963731 Kapitał zakładowy: 500 000 PLN

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Re: [boost] [unordered] unordered_set::erase() complexity bug?
by Christopher Crickmar 18 Mar '10

18 Mar '10

Given that the next iterator is meaningless for an unordered container and that cached_begin_bucket_ is always valid would it be bad manners to always return begin() ? Chris Crickmar

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[multi_index] hashed_index erase(iterator) performance issue
by Brad Higgins 17 Mar '10

17 Mar '10

Hello, I have encountered a performance issue with multi_index's hashed_index erase(iterator) routine. The erase(iterator) call returns an iterator to the next element in the data structure. When using this routine in a sparsely populated, large sized hash, it takes a very long time to complete. For example, in my program, I have rehashed the hash table to 5 million buckets, and added 600,000 elements. Adding the elements takes a matter of seconds. Then, I delete the elements. Deleting the elements takes hours. I have profiled the code, and it looks to me like the performance hit is rooted in the increment of the iterator by the erase(iterator) call. Since the hash is sparsely populated, the increment must advance over many empty buckets for each erase(iterator) call, in order to advance to the next valid element. My question is, why does the erase(iterator) function return an iterator at all? (In comparison, sgi's stl::hash_map's erase() returns void.) The hash is unordered, so the returned iterator is a random value, which I think decreases its usefulness (I expect most clients will discard the returned iterator.) Additionally, the same behavior can be achieved by clients who desire this behavior if they post-increment their iterator argument themselves. That is: // After this line, cur_itr's initial element will be erased, // AND cur_itr will be updated to the next element in the hash table hash_table.erase(cur_itr++); Is there some way to remove elements from the hash without taking this iterator increment hit? Would it be possible to add an erase routine (of some other name) which accepts an iterator argument, but does not automatically increment the argument? Thanks, Brad

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[log] Comments
by Vladimir Prus 17 Mar '10

17 Mar '10

Hello, I have a few comments and questions about the Boost.Log library currently being reviewed. This email is not actually a review as such. It will help if I explain where I'm coming from. I am most familiar with two logging mechanism. One is from KDE libraries. There, you have severities and component ids -- which are just integers. So, source code might have kDebug(9012) << "doing something"; There's GUI to configure which components have logging enabled, and there's a way to omit explict component id. Another logging mechanism is from Eclipse. There, you specify severity and component id -- this time a string. In KDE, output goes to a console. In Eclipse -- to a log file. I would those mechanism to be sufficient for all my needs. Looking at the proposed libraries, I see two major issues: * There's no default setup that is comparable with the two mechanisms above. BOOST_LOG_TRIVIAL has only severity and it appears adding component information is complicated. In a sense, it looks like the library provides building blocks, but not a solution I can immediately use. * I think the library elegantly uses various facilities like Boost.Parameter and lambda expressions to provide an easy interface. Unfortunately, it seems like it's failing to provide any other interface for folks who might be unhappy with lambdas and named parameters. There's a more detailed explanation of those major issues: * It appears that out of the box, the proposed library does not address this component/severity style of logging that I've explained above. The proposed solutions at: http://permalink.gmane.org/gmane.comp.lib.boost.devel/200793 sound relatively complex. * The example of specifying filter without lambda functions given in http://permalink.gmane.org/gmane.comp.lib.boost.devel/200793 is frankly scary. I believe that in most languages and environments I worked with, lambda functions are just convenient alternative to defining the same function explicitly. Why is in Boost.Log, lambda expressions are blessed with extra convenience? * Why can't I use the library without named parameters? Surely, there are low-tech ways to specify things. * Why does channel_logger has a *single* parameter, and still requires that you pass it via named parameter. That is: src::channel_logger<> cl("foobar"); produces incomprehensible error message. Other concerns: * The library went too far with namespaces. Why are *six* nested namespaces necessary? This appears to be just asking for extra typing for no good reason. * Why is trivial logging printing the sequental number of each log message? I don't think this helps anything. Also, it prints the thread "number", on my system a hex string. I am not sure thread id should be part of trivial logging. Finally, I think by default, everybody things of logging as glorified std::cout, so trivial logging better print messages to console, not to a file. * Why does the library have light_rw_mutex? I would really prefer if everything thread-related be located inside Boost.Thread, so that at least the code can be readily audited. * It appears that the default behaviour of fmt::attr is to throw is the attribute with such name is not found. This seems like a bad choice to me. A logging library should never fail -- it is the last resort at diagnosing a problem in the field, and if it throws by default, it's useless. * I have used the attached script to measure code size impact. The script basically creates a test file with a single function calling BOOST_LOG_TRIVIAL and measures the size of that function depending on the number of calls. I've got 139 bytes per call for 'g++ -Os' and 174 per call for 'g++ -O3', which seems nice. This is function code only. When counting file size I get 324 and 514 respectively. For reference, kDebug gives 136 and 328 of file_size_bytes per call. I guess these results are OK. * I see lots of warnings in slim_string.cpp, e.g: ../../../../libs/log/src/slim_string.cpp:237: warning: control reaches end of non-void function I'd recommend working with maintainer of boost/throw_exception.hpp to add noreturn attributes on gcc, and silence the warning in other ways on other compilers. * Building the library with threading=single results in unresolved references to pthread functions. I belive that library should not use any sync mechanisms in this case. Thanks, Volodya

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[log] Formal review
by Alexander Arhipenko 17 Mar '10

17 Mar '10

Boost.Log library formal review. > Please explicitly state in your review whether the library should be accepted. Yes, library should be accepted. Some explanation here. What means 'boost library' to me? It's very reliable, portable, efficient, sexy (in sense of code style) component that could satisfy from 90 to 95 % of regular user cases. Even if someone has an issue with such component - this issue could be resolved quickly (up to 1 hour). This quickness usually explained by clean library design and also by rich community support (the last sentence I've made based on my own experience with boost). IMHO, Boost.Log nicely fits into all the written above. Andrey spent many months (I've put an eye on Boost.Log in August 2008) polishing library's design, implementation, improving documentation. It would be nice to see the result of such huge efforts in Boost distribution. - What is your evaluation of the design? The overall design seems to be very orthogonal and does not mix different things together. - What is your evaluation of the implementation? I didn't dig deeply (except some functionality related to log rotation). At first glance, it's high quality, modern c++ code. It doesn't take too much time to understand it and make modifications. - What is your evaluation of the documentation? The first thing I except from any documentation - it's a "quick jumps" scenarios, i.e. workable small code snippets that compiles, works and give the user brief explanation on how to perform usual tasks using the library. I've found it in the latest docs and that was nice. Tutorial section is organized in 'from simple to complex things' form. This is very nice. Overall quality of the documentation is fine to me. - What is your evaluation of the potential usefulness of the library? Every application could really benefit from using logging. Especially server ones, that are running 24/7 without frequent human interaction. But I'm saying banal things now. In short, potential usefulness of such library is very high. - Did you try to use the library? With what compiler? Did you have any problems? Yes, I've tried it. gcc 4.1.2 (RHEL 5 x86_64, RHEL 5 i686). msvc 9 (Windows i686). The only problem I had it was warnings on gcc. But that was RC3 of the library, I guess Andrey addressed those issues in the latest version. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? We've integrated Boost.Log RC3 into our server application (in the end of January 2008). Now it's running in several production environments. I've spent several days writing tiny wrapper for Boost.Log. This wrapper was required due to reasons above: 1) I was not sure about the future: whether we would like to switch to the different logging library etc., nowadays answer to this question is categorical NO 2) All the components of application should have common logging formatting, logging levels, also some 'shortcuts' were needed (such as namespace aliases etc) Also, we did some Boost.Log profiling with valgrind (memcheck tool). As far as I remember, none issues were found. - Are you knowledgeable about the problem domain? Knowledgeable from the end-user point of view. I know, what I want to have from logging (e.g., various severities, filtering, log files rotation, thread-safety). - Questions I have one question in regards to log rotation. (I guess, I was asking it last year when RC3 was presented). Is it possible to setup log rotation in a following way: file.log - earlies log file (today) file1.log - older log file (yesterday) file2.log - oldest log file (the day before yesterday). This way Apache, Samba etc. performs rotation. Also, this rotation behavior is default in Python logging module. Also, this behavior is default in my wolrd ;). Many thanks to Andrey for Boost.Log contribution. Many thanks to Volodya for being a review manager. Regards

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[log] How to set/reset a channel-specific filter
by Andreas Huber 17 Mar '10

17 Mar '10

Hi We're currently reviewing Boost.Log and are wondering what is the best way to implement channel-specific filters. More precisiely, we are currently using the following "objects": - 2 sinks (one to debug output window, one to file) - several severity_channel_logger_mt objects, all declared with BOOST_LOG_DECLARE_GLOBAL_LOGGER, each of these is guaranteed to have a unique channel name For each of the channels, we would like to set a filter that only applies to records logged through the given channel. Since we can't seem to set a filter on the logger itself, we're wondering what is the best way to accomplish this? It seems as though both the core as well as the sinks only accept one filter. So, it seems we would have to a) assemble a filter expression that includes all the channels we'd like to filter on. *Or*, we could b) add exactly two sinks per logger object and set the desired filter on both sinks. Of course, we'd still want to only log to one file, so the question arises whether it is safe to have multiple sinks write to one file. If we go with method a), we'd need a way to enumerate all global loggers. If we go with b), we'd need a method to enumerate all the sinks in the system. We have not found a way to accomplish any of these tasks, how do we do this? Thanks & Regards, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header.

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[python]missing file
by K. Noel Belcourt 17 Mar '10

17 Mar '10

Hi, Trunk tests are dying with this error. error: Unable to find file or target named error: 'builtin_converters_ext' error: referred from project at error: '../libs/python/test' -- Noel

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[exception] Unreachable returns (was [log] Comments)
by Daniel James 17 Mar '10

17 Mar '10

On 15 March 2010 10:45, Vladimir Prus <ghost(a)cs.msu.su> wrote: > > * I see lots of warnings in slim_string.cpp, e.g: > > ../../../../libs/log/src/slim_string.cpp:237: warning: control reaches end of non-void function > > I'd recommend working with maintainer of boost/throw_exception.hpp to add noreturn attributes on > gcc, and silence the warning in other ways on other compilers. I think Boost.Exception already does that (http://www.boost.org/boost/exception/detail/attribute_noreturn.hpp) but this is something I've been meaning to ask about, as I had to deal with it for iostreams. Our normal solution is to use BOOST_UNREACHABLE_RETURN (http://tinyurl.com/yjjdzsh) but that doesn't work for compilers that don't understand a 'noreturn' attribute. I hacked together my own version (http://www.boost.org/boost/iostreams/detail/config/unreachable_return.hpp) but it's only a short term solution and could break if throw_exception changes. It would be nice to have a proper solution in Boost.Exception, or maybe there already is one and I missed it? Daniel

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