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Forthcoming Boost.Fiber review
by Nat Goodspeed 20 Jan '14

20 Jan '14

Hi all, The review of Boost.Fiber by Oliver Kowalke is scheduled from Monday, January 6th to January 12th. ----------------------------------------------------- About the library: Boost.Fiber provides a framework for micro-/userland-threads (fibers) scheduled cooperatively. The API contains classes and functions to manage and synchronize fibers similar to Boost.Thread. Each fiber has its own stack. A fiber can save the current execution state, including all registers and CPU flags, the instruction pointer, and the stack pointer and later restore this state. The idea is to have multiple execution paths running on a single thread using a sort of cooperative scheduling (versus threads, which are preemptively scheduled). The running fiber decides explicitly when it should yield to allow another fiber to run (context switching). Boost.Fiberinternally uses coroutines from Boost.Coroutine <http://ok73.funpic.de/boost/libs/coroutine/index.html>; the classes in this library manage, schedule and, when needed, synchronize those coroutines. A context switch between threads usually costs thousands of CPU cycles on x86, compared to a fiber switch with a few hundred cycles. A fiber can only run on a single thread at any point in time. docs: http://ok73.funpic.de/boost/libs/fiber/doc/html/index.html<http://ok73.ok.funpic.de/boost/libs/coroutine/doc/html/> git: https://github.com/olk/boost-fiber src: http://ok73.ok.funpic.de/boost.fiber.zip<http://ok73.ok.funpic.de/boost.coroutine.zip> --------------------------------------------------- Naturally, you need not wait until the review formally opens to start reviewing the Fiber library. Please always state in your review whether you think the library should be accepted as a Boost library! Additionally please consider giving feedback on the following general topics: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? Nat Goodspeed Boost.Fiber Review Manager ------------------------------

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GSoC 2014
by Bjorn Reese 20 Jan '14

20 Jan '14

Deadline for registring as a mentoring organization for GSoC 2014 is 14 Feb 2014. Should we start collecting ideas?

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[build] referring to a tool from an external project
by Eric Niebler 20 Jan '14

20 Jan '14

I'm trying to write a jamfile in an external project that uses boost. The jamfile should invoke the wave tool to preprocess some code as a build action. I have this: actions do_wave { $(>[2]) -o- --config-file wave.cfg $(>[1]) } W = /boost/libs/wave/tool/build//wave ; make preprocess : preprocess.cpp $(W) : do_wave ; I get: > error: Unable to find file or target named > error: '/boost/libs/wave/tool/build//wave' > error: referred to from project at > error: '.' > error: could not resolve project reference '/boost/libs/wave/tool/build' If I use this instead: W = /boost//wave ...it builds the wave dlls, not the command-line tool. So how do I tell it to build the tool? -- Eric Niebler Boost.org http://www.boost.org

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[Math] Permutations?
by Vee Kay 19 Jan '14

19 Jan '14

Hello, Would it be useful for Boost to provide a permutation class? The standard provides a couple of relevant functions (is_permutation, next_permutation) and Boost.Iterator offers a permutation_iterator adaptor. But as far as I can tell, no class that can be manipulated similarly to the mathematical object, something like this: https://gist.github.com/Kojirion/8503800 I admit I do not have many use cases in mind, just the impression this is a useful tool. As an example, once in a gui application I wished to animate the rearranging of a table; writing a permutation class made it easy to get the sequence of transpositions of rows and columns that would yield the desired result. (note though the above api doesn't include an asTranspositions() because I 'm not sure what is the most useful way to represent a transposition). I 'd be happy to hear your thoughts, Albert

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STL::MAP: Printing values only once ..
by Rahul Mathur 18 Jan '14

18 Jan '14

Hi, I have a input.txt file seperator by pipe '|' as - 40147|181|ORANGE|MIKE|XX||1000397900|3500 40148|373|ORANGE|BOB|XX||1078889400|4500 40149|673|ORANGE|TREY|XX||1095159900|5500 I only wish to have all the FIRST(ID=40147) and LAST FIELD(PRICE=3500) to be printed for three lines as given above. I am reading as - -- #include <iostream> #include <fstream> #include <sstream> #include <string> #include <boost/algorithm/string.hpp> using namespace std; struct FILE_INPUT { int ID; int Asset_ID; char T_Name[]; char Symbol[]; char Series[]; char Gap; int Date; int price; }; int main() { typedef std::map<int, int> unordmap; unordmap ask; FILE_INPUT fl_inp; memset( &fl_inp, 0, sizeof(fl_inp) ); ifstream in ("input.txt"); string s; const char delimiter = '|'; while ( getline (in, s) ) { trim( s ); if ( !s.empty() ) { stringstream strm( s ); string item; getline( strm, item ); stringstream stra( item ); string tmp; getline( stra, tmp, delimiter ); { stringstream strb( tmp ); strb >> fl_inp.ID; } getline( stra, tmp, delimiter ) { stringstream strb( tmp ); strb >> fl_inp.price; } ask.insert( std::make_pair((fl_inp.ID),(fl_inp.price)) ); unordmap::iterator pos = ask.begin(); for (pos = ask.begin(); pos != ask.end(); ++pos) { std::cout << "ID: " << pos->first << "\t" << "Price: " << pos->second << std::endl; } std::cout << " " << endl; } } } -- The map is being inserted with both ID as key and price as value but while printing it prints the values thrice as - ID: 40147 Price: 3500 ID: 40147 Price: 4500 ID: 40148 Price: 5500 ID: 40147 Price: 3500 ID: 40148 Price: 4500 ID: 40149 Price: 5500 The MAP should print all values together only once as - ID: 40147 Price: 3500 ID: 40148 Price: 4500 ID: 40149 Price: 5500 -- Can I maintain some checks to print all values simply once. Thanks.

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Re: [boost] Request for comments on super-project workflow doc
by Peter Dimov 18 Jan '14

18 Jan '14

Robert Ramey wrote: > John Maddox brought up the question of "bridge libraries" (?) . An > example would be the serialization library includes tests for boost > variant but doesn't use boost variant itself. So if one includes just the > modules which the serialization library uses to build - you'll get one set > of modules which won't include the ability to run the test set. If you > include all the modules which test set requires, you're going to include > half of boost. Yes, in general, there are three sets of dependencies: what the library headers depend on, what the library sources depend on, and what the library tests depend on, each a superset of the previous one. This doesn't make such a tool worthless or impossible though. And - FWIW - bridge libraries are something else, I think. The problem there is that, f.ex. a library X may not depend on the serialization library but making X's types serializable would. A bridge library XS could solve this by depending on both X and serialization and providing the necessary support. In principle, I've always argued that libraries should be designed in such a way so that adding support should not require including a header, but that's not the path of least resistance and if one doesn't specifically keep that requirement in mind, it's rare to see it satisfied. (And it's not always possible.) For example, here's how the smart pointers provide hash support without including anything: namespace boost { // hash_value template< class T > struct hash; template< class T > std::size_t hash_value( boost::intrusive_ptr<T> const & p ) { return boost::hash< T* >()( p.get() ); } } // namespace boost and this is how a type may be specified to be a (boost::bind) placeholder, again without any inclusions: namespace boost { template<class T> struct is_placeholder; template<int I> struct is_placeholder< my_placeholder<I> > { BOOST_STATIC_CONSTANT( int, value = I ); }; } // namespace boost

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Prefix Trie
by Michael Conlen 18 Jan '14

18 Jan '14

I recently discovered that there seems to be a lack of good Prefix Tries in C++. There are many basic ones and I think a C implementation ran all of 12 lines of code, but something with a nice interface and iterator seemed lacking. (Stop me if I'm missing something here) So I'm interested in developing Prefix (and possibly a Radix) Trie containers in C++. I could see a use for both sequence and map containers; however this would be a learning experience for me. If there's interest in such a creature I'm happy to go through the review process as necessary. Having said that, is there interest in having such a library and if so what are the pointers on what would be expected (particularly any boost-isms)? -- Mike

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[lockfree] Faster ring-buffer queue implementation
by Alexander Krizhanovsky 16 Jan '14

16 Jan '14

Hello, some time ago I've implemented lock-free multi-producer multi-consumer queue on ring buffer and recently I've compared it's performance with current (Boost 1.55.0) boost::lockfree::queue - it shows 50% better performance. I've made just a quick glance on the Boost implementation and noticed that it uses CAS operations which is basically slower than simple RMW (atomic increment in our case) on modern x86-64 hardware. Maybe I've made some mistake in boost::lockfree::queue usage. If so then I'll be obliged for pointing me out the problem in my benchmark. Otherwise I'm wondering if it has sense to integrate the queue implementation into boost::lockfree? The algorithm description is available at http://www.linuxjournal.com/content/lock-free-multi-producer-multi-consumer… The source code of the queue with the benchmark for boost::lockfree::queue: https://github.com/krizhanovsky/NatSys-Lab/blob/master/lockfree_rb_q.cc And the benchmark results are available here: http://natsys-lab.blogspot.ru/2014/01/natsys-lock-free-queue-in-comparison.… Thanks! -- Alexander Krizhanovsky NatSys Lab. (http://natsys-lab.com) tel: +7 (916) 717-3899, +7 (499) 747-6304 e-mail: ak(a)natsys-lab.com

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[Fibers] asio handler not respecting scheduler
by Eugene Yakubovich 16 Jan '14

16 Jan '14

While working on factoring out the scheduling algorithm, I noticed that when fibers are used with asio, the completion handler manually invokes the fiber: boost-fiber/include/boost/fiber/asio/detail/yield.hpp: In yield_handler<T>: void operator()( T t) { * ec_ = boost::system::error_code(); * value_ = t; fiber_->set_ready(); boost::fibers::detail::scheduler::instance()->spawn( fiber_); boost::fibers::detail::scheduler::instance()->run(); } Why does it call spawn? Shouldn't the scheduler (run method that follows) decide which fiber to run next? What happens if there's another fiber with a higher priority that's ready? A similar issue also comes up when launching a new fiber. The documentation supports the implementation in that the control immediately is transferred to the new fiber. However, shouldn't the scheduling algorithm decide when the new fiber should run? As an unrelated issue, I think this maybe a bug -- it's setting the active fiber to ready instead of waiting: void round_robin::yield() { <snip> // set active fiber to state_waiting active_fiber_->set_ready(); <snip> } Same issue in round_robin_ws and asio/round_robin. Regards, Eugene

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[Boost.Sync] no master branch?
by Eric Niebler 16 Jan '14

16 Jan '14

What is Boost.Sync and why doesn't its repository have a master branch? -- Eric Niebler Boost.org http://www.boost.org

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