July 2014 - Boost - lists.preview.boost.org

Lock free condition_variable or using shared_lock
by Kirk Liberty 30 Jul '14

30 Jul '14

I'm not too familiar with the mechanisms which underlie mutexs and conditionals, which is why I'm asking this question. Is it possible to modify condition_variable so that wait() can be called on shared_lock? The use case would be it is acceptable to release all threads waiting on a condition_variable when notify_all() is called. Using a unique_lock, every thread who wakes up will then have to obtain the lock before proceeding; this being a potential bottleneck. An even more performant alternative to using shared_lock would be with a dummy lock never blocks when dummy_lock.lock() is called. These are things I would like to contribute, but I need would need some guidance and a review of feasibility. Thanks for the help, Kirk

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News about proposed Boost.Application library
by Renato Forti 30 Jul '14

30 Jul '14

Hi All, This e-mail is only to inform news about proposed Boost.Application library. We have done many updates on version 0.4.9, see: - MinGW support; - The ‘auto_handler’ class to bind ‘stop’, ‘pause’, ‘continue’ and ‘single instance’ handlers automatically; - New samples for ‘auto_handler’; - Many fix and improvements on ‘Windows Server’ (Service API) mode; - Simplification of ‘handlers’ creation, now application context can by passed on constructor of functor, or user can use global version of it; - Docs are updated to version 0.4.9; - And many others small fixes. To know more, please visit: https://github.com/retf/Boost.Application Article (0.4.8) http://www.codeproject.com/Articles/756866/Build-a-Server-Application-using… (Prize winner in Competition "Best C++ Article of April 2014" ) Thanks

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[trac] Adding new components (Align, Type_Index)
by Michel Morin 30 Jul '14

30 Jul '14

Wouldn't it be better to add newly introduced libraries Align: glenfe (Glen Fernandes) Type_Index: apolukhin (Antony Polukhin) to trac components? Regards, Michel

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[quickbook] disambiguate overloaded function
by Benedek Thaler 30 Jul '14

30 Jul '14

Hi, I'm using quickbook and doxygen to generate my documentation. Suppose I have the following functions: func(int); func(std::string); They have separate reference pages, I'd like to link to them. However, I can't specify which one I mean using quickbooks funcref construct: [funcref func text] // results in: Reference to function 'func' is ambiguous. How can I specify the overload? Thanks, Benedek

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Re: [boost] [geometry] Querying for Points nearest to a Segment.
by Adam Wulkiewicz 30 Jul '14

30 Jul '14

2014-07-29 3:07 GMT+02:00 Jeremy Murphy <jeremy.william.murphy(a)gmail.com>: > Veering slightly off topic but still related to Geometry development, I've > hit some hurdles with the rtree index. I could create an index of points > easily but then couldn't query for the nearest neighbour of a segment. (I > assume this is simply not supported at present; is it forthcoming?) So I > created a ring or polygon from the segment and tried to query for the > points that it covers/intersects, which is a feature listed in the > documentation, but I've hit this compilation error: > > > /usr/include/boost/geometry/algorithms/detail/overlay/get_turn_info.hpp:932:32: > error: no matching function for call to > ‘boost::geometry::model::referring_segment<const > boost::geometry::model::d2::point_xy<double> >::referring_segment(const > boost::geometry::model::point<double, 2ul, > boost::geometry::cs::cartesian>&, const > boost::geometry::model::point<double, 2ul, > boost::geometry::cs::cartesian>&)’ > > This constructor for referring_segment looks OK to me, except maybe for the > 'const' qualifier on the arguments? > Which version of Boost are you using? Indeed nearest(segment, ...) shouldn't work in 1.55. However intersects(ring_or_poly) should. Could you prepare some minimal failing example? E.g. this compiles for me, using develop branch (upcomming 1.56) or 1.55 without one, marked line: #include <boost/geometry.hpp> #include <boost/geometry/index/rtree.hpp> #include <boost/geometry/geometries/segment.hpp> #include <boost/geometry/geometries/ring.hpp> namespace bg = boost::geometry; namespace bgi = bg::index; typedef bg::model::point<double, 2, bg::cs::cartesian> P; typedef bg::model::segment<P> Seg; typedef bg::model::ring<P> Ring; typedef bg::model::polygon<P> Poly; typedef P V; int main() { typedef bgi::rtree<V, bgi::linear<16, 4> > RT; //typedef bgi::rtree<V, bgi::quadratic<16, 4> > RT; //typedef bgi::rtree<V, bgi::rstar<16, 4> > RT; RT rt; V v; rt.query(bgi::nearest(Seg(), 1), &v); // Using 1.55 without this line rt.query(bgi::intersects(Ring()), &v); rt.query(bgi::intersects(Poly()), &v); } Regards, Adam

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[1.56.0 b1] Issue with mpl/is_convertable/asio
by Thomas Suckow 30 Jul '14

30 Jul '14

In testing '1.56.0 Beta 1' I have found that I am unable to compile https://github.com/splunk/pion on RHEL6_x64 Pion compiles fine with 1.55.0 I suspect the recurring "anonymous enum" is the kicker, though I am not sure where to even begin in diagnosing this. error: ‘const boost::asio::detail::buffer_sequence_adapter_base::<anonymous enum>&’ is/uses anonymous type error: no type named ‘type’ in ‘struct boost::is_convertible<const boost::asio::detail::buffer_sequence_adapter_base::<anonymous enum>&, const boost::iterator_range_detail::iterator_range_tag&>’ error: ‘value’ is not a member of ‘boost::mpl::aux::nested_type_wknd<boost::is_convertible<const boost::asio::detail::buffer_sequence_adapter_base::<anonymous enum>&, const boost::iterator_range_detail::iterator_range_tag&> >’ Full error log: http://pastebin.com/yeScQCpx If I get a chance I will see if I can reproduce this on a more modern compiler. Any assistance in correcting this before the 1.56.0 release would be appreciated. It also may or may not be related to http://thread.gmane.org/gmane.comp.lib.boost.devel/253259/focus=253261 Regards, Thomas

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quince: queries in C++ expressions
by Michael Shepanski 29 Jul '14

29 Jul '14

Hello, boost! I've released a library called "quince", which lets you use a relational database in C++ rather than SQL. So it provides an EDSL to wrap the SQL syntax, it converts between C++ types (including user-defined class types) and SQL column types, and it enforces type safety at compile-time. I wanted to ask whether there would be an interest in this for boost, so I subscribed to this list today, and for the first time I discover Roland Bock's sqlpp11, which does all of those things too. First of all I'd like to say: nice work Roland! The truth is, if I had seen sqlcpp11 earlier, I would not have had felt the need to write quince. Nevertheless, I did write it, and so of course it has a different set of features. The full doco is at http://quince-lib.com, but let me quickly point out a few differences from sqlpp11. 1. If you want some class to be mapped into SQL data, quince lets you write this sort of thing: struct point { float x; float y; }; QUINCE_MAP_CLASS(point, (x)(y)) extern database db; table<point> points(db, "points"); The macro QUINCE_MAP_CLASS uses a bit of Boost.Preprocessor magic and a bit of template metaprogramming to produce all the statically typed metadata that quince needs, regarding the user's type. There is no code generation step. 2. Quince's EDSL looks somewhat different. This is my first day as a student of sqlpp11, so I'm not really qualified to define the distinctions, but I think part of it is that sqlpp11 exposes the concept of column aliases, where quince does not, and quince is preoccupied with the idea of compositionality, in a way that sqlpp11 is not (as far as I know). Anyway you can see an example of the quince EDSL here: http://quince-lib.com/getting_started.html . 3. Just as sqlpp11 uses /connectors/, quince uses /backend libraries/, or /backends/. Currently I provide backends for PostgreSQL and sqlite. Unlike sqlpp11, however, I have not yet published the interface between quince and the backends. It's no secret --the whole lot is open source-- but I'm not yet ready to declare that I know all the customization points I'm going to need. 4. Quince provides mappings for std::tuple<T, ...> and boost::optional<T>, whenever it provides mappings for the Ts. E.g. a boost::optional<int32_t> is mapped as an INTEGER column with its NOT NULL constraint turned off. If you have a query q1 that produces results of type T1, and a query q2 that produces results of type T2, then q1.left_join(q2, some_predicate) produces results of type std::tuple<T1, boost::optional<T2>>. 5. An application can customize the representation of data in a particular database, or a particular table. 6. Quince does not currently provide bulk insert. (It's on my to-do list.) I've barely scratched the surface, but right now I have the impression that both products have their distinctive pluses. Keen to know your thoughts. Regards, --- Michael

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name of boost 1.56 tarball
by Menelaos Karavelas 29 Jul '14

29 Jul '14

Hello. Unlike previous versions which are named with underscores only, the boost 1.56 b1 tarball is named boost-1_56_0_b1.{zip, tar.gz, tar.bz, 7z}. Unpacking the tarball creates a boost-1_56_0_b1 directory instead of the expected one boost_1_56_0_b1 See also: http://sourceforge.net/projects/boost/files/boost/1.56.0.beta.1/ http://sourceforge.net/projects/boost/files/boost/1.55.0/ http://sourceforge.net/projects/boost/files/boost/1.54.0/ http://sourceforge.net/projects/boost/files/boost/1.53.0/ (older versions also follow the underscore filename pattern). Is there any particular reason for doing this? I suspect that it might cause problems to scripts looking for a specific pattern for the boost tar file and/or directory. All the best, - m.

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[functional/hash] Interface-breaking changes to hash_combine
by Joaquin M Lopez Munoz 29 Jul '14

29 Jul '14

Hi, There's been a number of internal changes to the implementation of boost::hash_combine during this year, with the result that the documented procedure: http://www.boost.org/doc/html/hash/reference.html#boost.hash_combine namely, seed ^= hash_value(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2), is no longer followed in all cases. This is a backwards compatibility breach --at the very least I think it should be documented. Best, Joaquín M López Muñoz Telefónica

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News about proposed Boost.Application library
by Matus Chochlik 29 Jul '14

29 Jul '14

On Tue, Jul 29, 2014 at 9:39 AM, Klaim - Joël Lamotte <mjklaim(a)gmail.com> wrote: > > It would be nice if get_symbol returned a smart pointer that contained a > shared_ptr to the library. When all such references are released, the > library can be unloaded. > > > > I disagree. In my experience it would be more useful if it contained a > weak_ptr to the library, with a centralised system keeping all loaded > libraries alive and allowing the used to unload the library explicitely. > The get_symbol return type would then be testable. > That way it is easier to find issues related to plugins and its still > possible for the user to prevent these issues at runtime. > +1

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