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concurrent garbage collector
by Taylor Holliday 23 Jun '13

23 Jun '13

Hey Boost, After struggling with breaking shared_ptr cycles in my app, I wrote a little concurrent garbage collector which uses boost::lockfree::queue. Its actually fairly general purpose, and I've released the code here: https://gist.github.com/wtholliday/5793270 Inspired by my question on stack overflow: http://stackoverflow.com/questions/17116189/concurrent-garbage-collection-f… I'm also working on releasing my unit test... its just quite dependent on other code. For the interface: the basic idea is you have a RootPtr<T> used to manage the collector's root set (please forgive my propensity for CamelCase). You have to explicitly manage references between collectable objects (via AddEdge and RemoveEdge functions), but I think that could be made safe using another smart pointer type which knows the collectable object which owns it. At this point I'm not too concerned about performance, as my object graphs aren't that big. I bet a GC guru could implement this without using a queue of events. Anyway, this is the kind of thing I'd love to see in boost someday, so it would be great to read your opinions of it :-) cheers - Taylor W. Taylor Holliday, Owner/Founder Subatomic Software, San Francisco

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Re: [boost] [Multiprecision] Does MP use references internally?
by Daryle Walker 21 Jun '13

21 Jun '13

Nearly all operators, besides assigning and dereferencing ones, are supposed to return by value. Changing that, even with the “innocuous” (unary)+, is surprising. Daryle W. Sent from Windows Mail From: John Maddock Sent: ‎Thursday‎, ‎June‎ ‎20‎, ‎2013 ‎4‎:‎13‎ ‎AM To: boost(a)lists.boost.org > Is Boost.MP giving users references-to-types instead of class types when > requesting a numeric type? Pointers may be objects in and of themselves, > but references aren't; they're just aliases; trying to intentionally use > them as first-class objects is arguably broken. I don't see why this is a problem, but the first error is coming from: auto const aa = +a, bb = +b; Now, in Boost.Multiprecision the unary operator+ is a noop that returns a reference to self, could that be a cause of the issue?

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ptr_map_adapter::insert non const key argument
by Gaetano Mendola 21 Jun '13

21 Jun '13

Hi, it seems that the method: std::pair<iterator,bool> ptr_map_adapter::insert( key_type& key, mapped_type x ) has the key argument non const? Is there a valid reason for it or it's just a mistake? Regards Gaetano Mendola

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How do I specify no padding bytes within a struct/class?
by Daryle Walker 20 Jun '13

20 Jun '13

I've never done this before, so I'm asking first: how do I specify that a struct/class should have no padding at all, at the start, end, or middle? My classes have internal arrays, and specifying no padding lets users use an array of classX<T> as an array of T (just like C++11 std::complex). Complier-specific answers are OK, as long as I can use preprocessor flags to isolate them. I have a preprocessor flag that's currently set to 0 to indicate that there's no packing. I'll change it to 1 whenever I get a compiler's packing support. Daryle W.

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[Multiprecision] Does MP use references internally?
by Daryle Walker 20 Jun '13

20 Jun '13

This may be an artifact of the compiler's error reporting mechanism, but the errors' expansion of the MultiPrecision type I'm using has reference types in it. Types from Boost.MP seem to be a shell class template that wraps an engine and several options. Some of the errors that pop up when using Boost.MP when using Boost.Test with my custom complex-number class: - Boost.MPL calls within Boost.Test complain that it's trying to get a pointer to a reference. - My own code uses arrays everywhere, and I get errors about making arrays to references. I'm not doing anything (too) advanced. Is Boost.MP giving users references-to-types instead of class types when requesting a numeric type? Pointers may be objects in and of themselves, but references aren't; they're just aliases; trying to intentionally use them as first-class objects is arguably broken. Daryle W.

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Re: [boost] [c++11]
by Niall Douglas 19 Jun '13

19 Jun '13

> I wasn't suggesting making the library strictly C++03-compatible. My main > point was that the library has to be compatible with _todays_ and even better > - _yesterdays_ compilers to be actually useful. My choice of "reasonable" time > frame is 3-5 years, as I mentioned. That includes VS 2008 and VS 2010, which > already had some C++11 features, including rvalue references. Making VS 2013 > absolute minimum is a no-go, IMHO. I don't think anyone is making VS2013 an absolute minimum - rather they're making variadic templates an absolute minimum. Something which any other compiler than VS has had for years, and something which unlike many, if not most other C++11 language features is something which lets you write a ton of stuff you simply can't write without them. Now, nothing in proposed Boost.AFIO uses variadic templates in a way not replaceable with preprocessor programming. However it very /nearly/ did: I had this neato bit of evil variadic instantiation which let you convert an unknown set of trailing args into a std::tuple<> for storage, then /unpack/ said std::tuple<> back into an unknown set of trailing args, all with perfect forwarding. Effectively it was a compile-time std::function<> implementation. As proposed Boost.AFIO is also a closure execution engine where that closure can take arbitrary args and return arbitrary returns, that evil variadic template machinery was really useful because it lets you skip using std::function<> with its implied virtual function call. As proposed Boost.AFIO currently nests, in the worst case scenario, a fully bound std::function<> calling a partially bound std::function<> calling a partially bound std::function<>, that's three nested virtual indirect function calls. Recent Intel CPUs can prefetch and branch predict two nesting levels, but they can't cope with three, so performance takes a real nose dive and hence one of the reasons we currently see a peak 80k IOPS. That evil variadic template machinery gets rid of that problem. And its only replacement is std::function<> - you *cannot* implement that functionality (pure compile time std::function<>) without variadic templates because you can't properly unpack them without. None of this matters for proposed Boost.AFIO. But it certainly matters for the forthcoming C++11 only libraries coming soon to Boost, because they make /very/ heavy usage of functionality only possible with variadic templates. That means that they will require, as an absolute minimum for VS, VS2013 or Nov 2012 CTP. Other C++11 features one can make do without without too much cost, but losing variadic templates means a ton of extra source code complexity, much longer compile times and chopping out a lot of what C++11 enables which simply can't be done in C++03. I suspect that those libraries are probably going to force a new "variadic template support is mandatory" category of Boost libraries, probably sooner rather than later. I agree it's going to be frustrating for those stuck with older compilers: I pity those whose employers force MSVC6 on them to this very day. Niall --- Opinions expressed here are my own and do not necessarily represent those of BlackBerry Inc.

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Can't compile code with BOOST_LOG_TRIVIAL
by ... ... 19 Jun '13

19 Jun '13

Hi, I am trying to compile this code : #include <boost/log/trivial.hpp> int main(void){ BOOST_LOG_TRIVIAL(trace) << "boost log is working"; return EXIT_SUCCESS;} And I get the following error message : g++ -o test Capture.o ffmpegTools.o FluxVideoModifie.o test.o vizILogger.o -lavformat -lavcodec -lavutil -lswscale -lopencv_core -lopencv_highgui -lboost_filesystem -lboost_log_setup -lboost_log -lz -lpthread -ldl -lm test.o: In function `main':/home/exploit/git/VIZIRD-CAPTURE/proj/capture//test.cpp:39: undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'/home/exploit/git/VIZIRD-CAPTURE/proj/capture//test.cpp:39: undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'test.o: In function `boost::log::v2s_mt_posix::record::reset()':/usr/local/include/boost/log/core/record.hpp:153: undefined reference to `boost::log::v2s_mt_posix::record_view::public_data::destroy(boost::log::v2s_mt_posix::record_view::public_data const*)'test.o: In function `boost::log::v2s_mt_posix::record boost::log::v2s_mt_posix::sources::basic_composite_logger<char, boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level>, boost::log::v2s_mt_posix::sources::multi_thread_model<boost::log::v2s_mt_posix::aux::light_rw_mutex>, boost::log::v2s_mt_posix::sources::features<boost::log::v2s_mt_posix::sources::severity<boost::log::v2s_mt_posix::trivial::severity_level>, void, void, void, void, void, void, void, void, void> >::open_record<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> >(boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> const&)':/usr/local/include/boost/log/sources/basic_logger.hpp:457: undefined reference to `boost::log::v2s_mt_posix::core::get_logging_enabled() const'test.o: In function `~record_pump':/usr/local/include/boost/log/sources/record_ostream.hpp:278: undefined reference to `boost::log::v2s_mt_posix::aux::unhandled_exception_count()'test.o: In function `record_pump':/usr/local/include/boost/log/sources/record_ostream.hpp:259: undefined reference to `boost::log::v2s_mt_posix::aux::stream_provider<char>::allocate_compound(boost::log::v2s_mt_posix::record&)'/usr/local/include/boost/log/sources/record_ostream.hpp:259: undefined reference to `boost::log::v2s_mt_posix::aux::unhandled_exception_count()'test.o: In function `~auto_release':/usr/local/include/boost/log/sources/record_ostream.hpp:243: undefined reference to `boost::log::v2s_mt_posix::aux::stream_provider<char>::release_compound(boost::log::v2s_mt_posix::aux::stream_provider<char>::stream_compound*)'test.o: In function `boost::log::v2s_mt_posix::sources::aux::severity_level<boost::log::v2s_mt_posix::trivial::severity_level>::set_value(boost::log::v2s_mt_posix::trivial::severity_level)':/usr/local/include/boost/log/sources/severity_feature.hpp:135: undefined reference to `boost::log::v2s_mt_posix::sources::aux::get_severity_level()'test.o: In function `boost::log::v2s_mt_posix::record boost::log::v2s_mt_posix::sources::basic_logger<char, boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level>, boost::log::v2s_mt_posix::sources::multi_thread_model<boost::log::v2s_mt_posix::aux::light_rw_mutex> >::open_record_unlocked<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> >(boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> const&)':/usr/local/include/boost/log/sources/basic_logger.hpp:260: undefined reference to `boost::log::v2s_mt_posix::core::open_record(boost::log::v2s_mt_posix::attribute_set const&)'test.o: In function `boost::log::v2s_mt_posix::core::push_record(boost::rv<boost::log::v2s_mt_posix::record>&)':/usr/local/include/boost/log/core/core.hpp:308: undefined reference to `boost::log::v2s_mt_posix::core::push_record_move(boost::log::v2s_mt_posix::record&)'collect2: ld returned 1 exit statusmake: *** [test] Error 1 In my makefile I added the links :LIBS_boost = -lboost_filesystem -lboost_log_setup -lboost_log And i have my libraries correctly installed because the command : $ sudo ldconfig -p | grep boost_l display :libboost_log_setup.so.1.53.0 (libc6,x86-64) => /usr/local/lib/libboost_log_setup.so.1.53.0libboost_log_setup.so (libc6,x86-64) => /usr/local/lib/libboost_log_setup.solibboost_log.so.1.53.0 (libc6,x86-64) => /usr/local/lib/libboost_log.so.1.53.0libboost_log.so (libc6,x86-64) => /usr/local/lib/libboost_log.solibboost_locale.so.1.53.0 (libc6,x86-64) => /usr/local/lib/libboost_locale.so.1.53.0libboost_locale.so (libc6,x86-64) => /usr/local/lib/libboost_loc Can you help me please ? Thanks,Guillaume Bersac237bis rue de Pessac33000 Bordeaux06.65.30.89.43

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Weirdness in SVN
by Marshall Clow 19 Jun '13

19 Jun '13

Ok, this is quite worrisome to me. This morning, bug #6136 was reopened: https://svn.boost.org/trac/boost/ticket/6136 This is an "unused variable warning" in Boost.DateTime. I fixed this bug in the trunk: https://svn.boost.org/trac/boost/changeset/80699 I merged this bug fix (and several others) to the release branch: https://svn.boost.org/trac/boost/changeset/80797 But the files (both trunk and release) appear not to contain the change. If I do a "svn diff", the changes appear in the diff, but the file doesn't contain the change. I checked the other files referenced in change set 80797, and they appear to be fine - just this one. Any idea what could be happening here? My only explanation at the moment is that "Subversion is lying to me", and that's both (a) a huge potential problem, and (b) doesn't suggest a course of action. $ svn diff trunk/boost/date_time/format_date_parser.hpp -r 80698 Index: trunk/boost/date_time/format_date_parser.hpp =================================================================== --- trunk/boost/date_time/format_date_parser.hpp (revision 80698) +++ trunk/boost/date_time/format_date_parser.hpp (working copy) @@ -256,7 +256,6 @@ // skip leading whitespace while(std::isspace(*sitr) && sitr != stream_end) { ++sitr; } - charT current_char = *sitr; short year(0), month(0), day(0), day_of_year(0);// wkday(0); /* Initialized the following to their minimum values. These intermediate @@ -290,7 +289,6 @@ } wkday = mr.current_match; if (mr.has_remaining()) { - current_char = mr.last_char(); use_current_char = true; } break; @@ -310,7 +308,6 @@ } wkday = mr.current_match; if (mr.has_remaining()) { - current_char = mr.last_char(); use_current_char = true; } break; @@ -326,7 +323,6 @@ } t_month = month_type(mr.current_match); if (mr.has_remaining()) { - current_char = mr.last_char(); use_current_char = true; } break; @@ -342,7 +338,6 @@ } t_month = month_type(mr.current_match); if (mr.has_remaining()) { - current_char = mr.last_char(); use_current_char = true; } break; @@ -438,7 +433,6 @@ itr++; if (use_current_char) { use_current_char = false; - current_char = *sitr; } else { sitr++; $ svn diff trunk/boost/date_time/format_date_parser.hpp -r 80699 $ -- Marshall Marshall Clow Idio Software <mailto:mclow.lists@gmail.com> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait). -- Yu Suzuki

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[range] Best way to count the elements in a filtered range?
by Gonzalo Brito Gadeschi 19 Jun '13

19 Jun '13

I wonder what is the recommended way to count the elements in a filtered range. Let range be a random access range, and filter the result of filtered(predicate), auto filtered_range = range | filter; count_if( filtered_range, [](const&){ return true; }); // (& omitted in lambda) counts the elements in a filtered range. _If_ this is the best way to count the elements in a filtered range, what about defining Range boost::count(Range&& r); to count all element in the range? It could call size() if available and count_if otherwise. Bests, Gonzalo BG

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[mailing list] Duplicated thread - Best way to proceed
by Gonzalo Brito Gadeschi 19 Jun '13

19 Jun '13

The thread: [boost] [range] Best way to count the elements in a filtered range? I sent an email with an unregistered email adress to the list. As expected, I did not receive a confirmation about the mail being accepted. I resent the mail with my registered email adress. As expected, the new mail was accepted. However, the unaccepted mail started getting replies. - What is the best way to proceed? - Why did the email sent with the unregistered email address get replies? - Shouldn't it have been rejected right away? Bests, Gonzalo BG

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