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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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