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[flyweight] Review summary
by Ion Gaztañaga 17 Feb '08

17 Feb '08

Hi to all, I've just written a summary of the flyweight review that tries to point out the main requests, questions and comments from reviewers and Joaquin's replies to those. If someone thinks I've missed some important point, please let me know. Joaquín is already correcting the pointed issues and thinking about alternatives on the keyed_flyweight issue. I hope we can definitely solve them satisfactorily in a short period of time. Here we go: -------------------------- Beginning of summary -------------------------- ------------------------- *Tim Blechmann’s review:* ------------------------- Design: Good. Suggests using read-write locks to improve concurrency since most operations will be searches. Implementation: fine Documentation: good Usefulness: quite useful to reduce memory footprint. Try to use the library: no Effort: Read documentation and compare it with his own implementation Knowledgeable about the problem domain: yes Accept the library: yes This reviews starts a thread about the correct read-write lock implementation for flyweight: 1) Joaquín points out that the library is based on insert(x) so a good candidate can be: readwrite_lock l(mutex); l.read_lock(); if(h=find(x))return h; else{ l.unlock(); l.write_lock(); h=insert(x); } Unfortunately read-write locks were removed due to a bug so this issue will be put under Future Work section for now. 2) Alberto Ganesh Barbati: suggests using hinted insert to improve performance in cases where find(x) fails and try to get a O(1) insertion. He also suggests using promotion or/and upgradable mutexes. 3) Joaquín thinks promotion/upgradable mutexes are not necessary. Read-write locks/upgradability/hints will need more thinking to maintain current policy orthogonality and the issue needs time. As mentioned, the issue will be revised when rw locks are available in Boost. Review manager note: I think that using “hint” needs atomic convertibility, because the “hint” can be invalidated by an erasure between unlock_sharable() and lock_sharable() and hint insertion does not guard against invalidated hints, but only against non invalidated but non-optimal hints. ------------------------- *John Reid’s review:* ------------------------- Design: Very good. Suggests intermodule_holder as the default holder. Implementation: Ok. Documentation: Clearly written and well thought out. He would like to see more examples and the inclusion of test code. Usefulness: High Used the library: No Effort: A quick read through the tutorial and the examples Knowledgeable about the problem domain: Not a design patterns expert but using C++ for 15 years. Accept the library: yes 1) Joaquín replies that intermodule_holder performs a way more expensive static initialization process than static_holder (needs shared memory). Another reason for not including this is that Boost.Interprocess (on which intermodule_holder depends) is not universally supported. Agrees to improve examples. 2) John suggests documenting intermodule_holder limitations 3) Joaquín agrees documenting these limitations ------------------------- *Marcus Lindblom’s review* ------------------------- Design: Very nice. Comments: namespace should be boost::flyweight. Factory should be called store Implementation: Not looked at thoroughly. Documentation: Great! Comments: the reference page, the first header ("boost/flyweight.hpp") doesn't link to anything? flyweight.hpp page misses to mention the tag argument in the first list of parametrization. Usefulness: High. Used the library: Nope. Effort: Quick reading. (1h) Knowledgeable about the problem domain: Yes Accept the library: Yes 1) Joaquín says that namespace issues are related to compiler bugs and the namespace conforms Boost rules explained at "For those who are really interested in namespaces" at http://tinyurl.com/ywb9n7 Factory name was chosen because most descriptions of the flyweight design pattern use this same terminology: http://tinyurl.com/ys5k3q Agrees to fix documentation problems with Firefox. ------------------------- *Matias Capeletto’s review* ------------------------- Design: Great. Implementation: Quick look. Documentation: Good. Typo spotted. Usefulness: High Used the library: gcc 4.1.3, under Linux Effort: Followed the library progress from the beginning Knowledgeable about the problem domain: Yes Accept the library: Yes 1) Joaquín: Typo fixed David Sankel’s review Design: Very well designed. Suggests a configuration option for equality segmantics. Implementation: He hasn't looked at much code, so I have no opinion here Documentation: Good Usefulness: Good Used the library: No Effort: An in depth study of the documentation Knowledgeable about the problem domain: Not until this review Accept the library: Yes 1) Joaquín says it’s trivial to override the default equality on a per case basis: typedef flyweight<whatever,...> fw_t; inline bool operator==(const fw_t& x,const fw_t& y) { return &x.get()==&y.get(); } ------------------------- *Vicente Botet’s review* ------------------------- Design: Good. Issues: * The tests performed on example5 should be extended with a intermodule_holder specifier. Joaquín’s answer: there is no need for that since it’s only performed in the initialization. * On platforms on which static variables are unique inter DLL the intermodule_holder specifier type can be a static_holder_class. Joaquín’s answer: Ok. * Holder specifier renaming. Maybe static_holder by module_holder, and intermodule_holder by process_holder? Joaquín’s answer: Agrees to revise names but he’s not found good alternatives. * Add an exclusive core specifier Joaquín’s answer: Added to Future Work section. Implementation: Quite good * Minor correction The documentation states that the ..._specifier must be a ..._marker, but this is not needed for the ..._class Joaquín’s anwswer: This ability used to be documented at the reference, but I've just checked and it is no longer there, I'll restore that bit. * refcounted_value is a class that could be public. Why it is declared in the namespace detail. Joaquín’s answer: It is an implementation detail, the user won't ever be exposed to it. * could you explain why detail::recursive_lightweight_mutex is needed and boost::detail::lightweight_mutex is not used directly? Joaquín’s answer: Recursive mutexes are needed when constructing composite complexes with flyweight<>. Documentation: Good. Issues: * Some more elaborated examples suggested. Joaquín’s answer: I'll try to extend the examples section. * intermodule_holder specifier: A reference to a document explaining the problem with platforms not ensuring the unicity of static variables when DLL are used will be welcome. Joaquín’s answer: I'm no expert here, but I'd say that platforms without static var unicity across dynamic modules are the majority rather than the exception. * Reference section: The reference section was much more hard to follow. I think that the interactions between the different classes are very hard to describe using the current style. Joaquín’s answer: It tries to keep the level of formality you find at the C++ standard. The idea is you go to the reference for exact, authoritative information. * An implementation section will help to understand how all this works, describing the interactions between the core and the policies. Joaquín’s answer: I'd much prefer to concentrate on improving the part on extending the library without disclosing too much about how things are assembled internally. * Add performance section Joaquín’s answer: Ok. * Rational: Adding of the map versus set problem explanation.??? Usefulness: Good Used the library: No. Effort: In-depth reading of the docs and implementation Knowledgeable about the problem domain: Yes Accept the library: Yes ------------------------- *Neil Hunt’s review* ------------------------- Design: Good Implementation: Good Documentation: He didn't read it all closely. * Some performance indicators or at least discussion of the tradeoff of extra hashing vs reduced dynamic allocations would be useful. Joaquín’s answer: ok Usefulness: Useful Used the library: No Effort: A moderate investigation. Knowledgeable about the problem domain: Yes Accept the library: Yes ------------------------- *Alberto Ganesh Barbati’s review* ------------------------- Design: Very good. Issues: * It doesn't fully grasp the essence of the flyweight pattern because of a major flaw. The flaw is the fact that an object needs to be created in order to check whether an equivalent flyweight exists or not. Implementation: Well done. Issues: * I strongly disagree with the choice of the term "factory" for a component that actually only acts as a storage. Documentation: Very well written. Issues: * The policies are indeed properly described, but the bare description is not very helpful in showing how to write a new policy Usefulness: Useful if the flaw I described before could be addressed Used the library: gcc 3.4.5 (mingw) Effort: A couple of hours. Knowledgeable about the problem domain: Yes. Accept the library: Reluctantly, the answer is no. He encourages the maintainer to consider addressing the issues I raised here, in which case I am ready to change my opinion. 1) Joaquín’s answer: * Instantiating a flyweight<T> will always create a temporary T (and hopefully just one when we get rvalue refs and variadic templates). The purpose of the library is *not* to avoid constructing expensive objects, it is to reduce memory consumption through object sharing. Collateral benefits include increased performance in object passing around. * GoF introduces a key type K into the pattern that is used to retrieve the actual values of T. So, we have a one-to-one relation KT, i.e. there exists a stateless function f of the form “T f(const K&)”. My analysis led me to conclude that the right approach is to assume that K==T. * Joaquín will investigate the potencial of the LookupFactory (factories that, additionally to the insert memfun, provide a find memfun) pattern, described at http://lists.boost.org/Archives/boost/2008/01/132798.php * I decided to keep "factory" because this component is obviously * related to the element of the same name in GoF and oher descriptions * of the pattern. * I’ll refine the reference section to make it easier write custom policies. 2) Alberto’s answer: I have another case in an project I am working on: in a 3D application, I have heavyweight 3D mesh objects that might be shared among several actors. The key of a 3D mesh is just its filename. I don't want to load an entire mesh into memory just to find out that I have it already. 3) Joaquín proposes the keyed_flyweight: struct character { character(char c):c(c){} char c; }; int main() { // fw_t objects are constructed from chars // but are convertible // to character. typedef keyed_flyweight<char,character> fw_t; // creates an internal character('a') fw_t x1('a'); // same shared value as x1, zero temporary character's fw_t x2('a'); // creates an internal character('b') fw_t x3('b'); } 4) Alberto proposes unifying keyed and non-keyd with just one flyweight class template: * we have two types: key_type for keys and value_type for values. The two types can be coincident (non-keyed proposal) * the constructor of flyweight semantically takes keys, not values * keys (not values) are fed as-is to the factory insert() method: it's up to the factory to determine whether the key is already present and if it's not present to construct the corresponding value. * the insert() method returns a handle * the factory provides a way to extract values from handles * The rest of the design would more or less stays exactly the same. 5) Joaquín’s answer to Alberto’s unified flyweight: I'd rather factories remained dumber so that all this intelligence is implemented in the core because: * STL associative containers are either set-like * (key_type=value_type) or map-like (T != value_type != key_type, because T == mapped_type). * The container would have to deal with a more general notion of key extraction. Boost.MultiIndex can do that, but I don't want to tie flyweight to that lib. Review manager note: The discussion went a bit further but the essence is that Joaquín has proposed alternatives and is ready to further discuss the issue because flyweight won’t be ready until Boost 1.36. I encourage Joaquín, Alberto and other contributors to discuss the issue in the future again. ------------------------- *John Torjo’s review* ------------------------- Design: Ok. Implementation: Ok. http://svn.boost.org/svn/boost/sandbox/flyweight/libs/flyweight/doc/tutoria… I think there could be a simpler way to do this: http://www.entropygames.net/globals.htm Documentation: Very nice Usefulness: Very useful. Used the library: No. Effort: 1.5h Knowledgeable about the problem domain: Yes Accept the library: Yes. ------------------------- *Markus Werle's review* ------------------------- Design: Not reviewed Implementation: Not reviewed Documentation: Good Usefulness: Yes Used the library: No Effort: Moderate Knowledgeable about the problem domain: No Accept the library: Yes ------------------------- *Kevin Sopp’s review* ------------------------- Design: Good. A way to get usage statistics about the flyweights would be nice (Joaquín agrees) Implementation: Good Documentation: Good Usefulness: Good Used the library: Yes Effort: Moderate Knowledgeable about the problem domain: Yes Accept the library: Yes Other accepted suggestions coming from non-review posts: Add assertions to catch static variables destruction ordering problems with flyweight. The refcounted tracking policiy can detect such illegal situations (an entry is destroyed with a refcount!=0). -------------------------- End of summary -------------------------- Ion Gaztañaga - Review Manager -

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Regex Library+ Urgent
by Srinivas Chamarthi 17 Feb '08

17 Feb '08

HI, I have built regex library with stlport using the following command nmake -fvc8-stlport.mak ( I copied vc71-stlport.mak to vc8-stlport and updated vc71 to vc80). It created *boost_regex-vc80-mt-gdp-1_34_1.lib *and dll files. I have defined the two variables in my application in the same order. #define #define __STL_DEBUG #define BOOST_REGEX_DYN_LINK Iam getting the following errors. can any 1 help me ? I am not able to proceed further with my application. I am stuck for last four days. I have seen some posts on this but not able to find the solution. I have defined the boost regex lib path properly. Appreciate your help Error 5 error LNK2019: unresolved external symbol "public: bool __thiscall boost::re_detail::perl_matcher<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> >,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > >::match(void)" (?match@?$perl_matcher@PBDV?$allocator@U?$sub_match@ PBD@boost@@@stlp_std@@U?$regex_traits@DV?$w32_regex_traits@D@boost @@@boost@@@re_detail@boost@@QAE_NXZ) referenced in function "bool __cdecl boost::regex_match<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> >,char,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > >(char const *,char const *,class boost::match_results<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> > > &,class boost::basic_regex<char,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > > const &,enum boost::regex_constants::_match_flags)" (??$regex_match@ PBDV?$allocator@U?$sub_match@PBD@boost@@@stlp_std@@DU?$regex_traits@DV ?$w32_regex_traits@D@boost@@@boost@@@boost@@YA_NPBD0AAV?$match_results@PBDV ?$allocator@U?$sub_match@PBD@boost@@@stlp_std@@@0@ABV?$basic_regex@ DU?$regex_traits@DV?$w32_regex_traits@D@boost@@@boost@@@0@W4_match_flags@ regex_constants@0@@Z) ExprEvaluator.obj Error 6 error LNK2019: unresolved external symbol "private: void __thiscall boost::re_detail::perl_matcher<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> >,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > >::construct_init(class boost::basic_regex<char,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > > const &,enum boost::regex_constants::_match_flags)" (?construct_init@?$perl_matcher@PBDV?$allocator@U?$sub_match@PBD@boost @@@stlp_std@@U?$regex_traits@DV?$w32_regex_traits@D@boost@@@boost@@@ re_detail@boost@@AAEXABV?$basic_regex@DU?$regex_traits@ DV?$w32_regex_traits@D@boost@@@boost@@@3@W4_match_flags@regex_constants@3@@Z) referenced in function "public: __thiscall boost::re_detail::perl_matcher<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> >,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > >::perl_matcher<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> >,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > >(char const *,char const *,class boost::match_results<char const *,class stlp_std::allocator<struct boost::sub_match<char const *> > > &,class boost::basic_regex<char,struct boost::regex_traits<char,class boost::w32_regex_traits<char> > > const &,enum boost::regex_constants::_match_flags,char const *)" (??0?$perl_matcher@ PBDV?$allocator@U?$sub_match@PBD@boost@@@stlp_std@@U?$regex_traits@DV ?$w32_regex_traits@D@boost@@@boost@@@re_detail@boost@@QAE@PBD0AAV ?$match_results@PBDV?$allocator@U?$sub_match@PBD@boost@@@stlp_std@@@2@ABV ?$basic_regex@DU?$regex_traits@DV?$w32_regex_traits@D@boost@@@boost@@@2@W4 _match_flags@regex_constants@2@0@Z) ExprEvaluator.obj

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getline from boost::iostream::filtering_streambuf
by Holger Bast 17 Feb '08

17 Feb '08

I want to read line by line from a gzipped document. I first do: std::ifstream file(fileName.c_str()); boost::iostreams::filtering_streambuf<boost::iostreams::input> in; in.push(boost::iostreams::gzip_decompressor()); in.push(documentFile); However, then the obvious: string line; while(std::getline(in, line)) { ... } does not compile. Is there really no getline for filtering_streambuf? If not, what is the best way to write one? I tried reading character by character using boost::iostream::get(in) but that looks terribly inefficient to me, and is not nice code. Thanks for your help, Holger

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Support for the Logic paradigm in C++ (with Castor)
by Naik, Roshan 16 Feb '08

16 Feb '08

This library (Castor) may be of interest to the "paradigm redefining" Boost community also ... -Roshan Naik ------------------------------------------------------------ Castor is a pure C++ Library that introduces the Logic paradigm (LP) into C++. Although LP has been well explored in Computer science, it remains under utilized in main stream software development due to lack of support in popular programming languages. Among the few languages that do support it, Prolog is perhaps the most commonly known. Instead of attempting to embed a Logic interpreter or other heavy weight engine into C++, Castor integrates LP using a few simple library primitives. This unique approach allows a natural and deep integration of declarative code into the language, and also provides the flexibility of combining Logic with other paradigms natively supported by C++ such as OOP, generics etc. STL concepts like iterators ,containers and streams can also be used in declarative code. Castor is an open source library distributed under the MIT license (http://www.opensource.org/licenses/mit-license.php) It is relatively small (under 5k LOC) and can be downloaded for free from http://www.mpprogramming.com For an introductory tutorial on LP and understanding its use in C++ refer to http://www.mpprogramming.om/resources/CastorTutorial.pdf Feedback, comments and contributions are welcome.

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Can not compile 'adj_list_ra_edgelist.cpp'
by yi zhang 16 Feb '08

16 Feb '08

Hi, everyone 'adj_list_ra_edgelist.cpp' is a simple example of bgl, but I can not compile it with gcc 3.4.4 on cygwin/windows xp. Following are the codes: #include <boost/config.hpp> > #include <iostream> > #include <boost/graph/adjacency_list.hpp> > > int > main() > { > using namespace boost; > typedef adjacency_list<vecS, vecS, bidirectionalS, no_property, > property<int, edge_weight_t, property<int, edge_index_t> >, > no_property, vecS> Graph; > > const std::size_t n = 3; > typedef std::pair<std::size_t, std::size_t> E; > E edge_array[] = { E(0,1), E(0,2), E(0,1) }; > const std::size_t m = sizeof(edge_array) / sizeof(E); > Graph g(edge_array, edge_array + m, n); > for (std::size_t i = 0; i < m; ++i) > std::cout << edges(g).first[i] << " "; > std::cout << std::endl; > > return 0; > } The error is located in the line 28, i.e. edges(g).first[i]. I think edges(g).first has the type of adjacency_list::edge_iterator. But how can I understand 'edges(g).first[i]'? Thanks, Timothy Zhang

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Pointers as graph vertex property
by Christian Sturz 15 Feb '08

15 Feb '08

Hi, I've a question about Boost Library Graphs. My Boost Graph is defined as: typedef boost::adjacency_list< boost::vecS, boost::vecS, boost::directedS, boost::property< boost::graph_name_t, std::string >, boost::property< boost::vertex_index_t, ClassA* > > Boost_Graph; So, I want to have a pointer to an entity of class ClassA as vertex property "vertex_index". However, when I try to access this property via a property map boost::property_map< Boost_Graph, boost::vertex_index_t >::type vertexNameMap = get( boost::vertex_index, g ); with vertexNameMap[v] (where v is Vertex_Type) the compiler tells me that the property is not of type 'ClassA*' (as I would expect) but of type 'size_t'. Why? I thought that for the definition of boost::property< boost::vertex_index_t, ClassA* > ClassA* is the template value and defines the type of the property "vertex_index". Any ideas how I can manage it to store pointers as vertex property? Regards, Christian -- Psst! Geheimtipp: Online Games kostenlos spielen bei den GMX Free Games! http://games.entertainment.web.de/de/entertainment/games/free

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boost.xpressive - unicode supported?
by Amit 15 Feb '08

15 Feb '08

Hi, I am wondering whether Xpressive supports Unicode completely, as Regex does through ICU? I found out about Xpressive only recently, and it being header only is obviously a big plus; but my app is all about i18n, and makes use of regex patterns with character category predicates (e.g. [[:P*:]]). I read the docs for Xpressive - while it does claim to support Unicode, they have not provided a list of valid patterns, and unless they have code charts as part of headers, I don't see how they can provide full Unicode support with depending on ICU or something... Any clarification would be extremely helpful. Thanks Amit

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[utility] question about enable_if
by Christian Henning 15 Feb '08

15 Feb '08

Hi there, I'm having a problem with using enable_if. For the sake of simplicity I have created the following test code which compiles fine. #include <string> #include <boost/mpl/and.hpp> #include <boost/utility/enable_if.hpp> using namespace std; using namespace boost; struct reader {}; template< typename String > struct is_string : public mpl::false_ {}; template<> struct is_string<std::string> : public mpl::true_ {}; template< typename Device > struct is_device : public mpl::false_ {}; template<> struct is_device<reader> : public mpl::true_ {}; template< typename String> struct enable_if_helper { typedef typename enable_if< typename is_string< String >::type >::type type; }; template<typename Device > void foo( typename enable_if< typename is_device<Device>::type >::type* ptr = 0 ) {} template<typename String> void foo( typename enable_if< typename is_string<String>::type >::type* ptr = 0 ) { foo<reader>(); } int main(int argc, _TCHAR* argv[]) { foo<std::string>(); return 0; } If I changed the string foo() interface to use the enable_if_helper the code doesn't compile anymore. Why is that? I've changed the foo ( with the string template parameter ) to the following: template<typename String> void foo( typename enable_if_helper< String >::type* ptr = 0 ) { foo<reader>(); } Anyone can help me out here? I'm using Visual Studio 8. Thanks, Christian

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[xpressive] Pattern problems (newbie)
by ope 14 Feb '08

14 Feb '08

Hi, I'try to build a regex for an ibis file, the line I'm interested looks like: [IBIS Ver] 3.2 | Used for template variations" where '|' is an optional comment identifier with the (therefore optional) comments follows. I'm interested in the version self: "3.2" to create a parser using a factory. Using egrep '^\[IBIS Ver]' success. From docs I tested the dynamic regex $ perl -p -e '(\\w+) (\\w+)!' "Hello World" which fails (syntax error at -e line 1, near "+) ") The regex are perl syntax, isn't? What is the regex for my IBIS Ver identifier? Thanks, Olaf

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[iostreams] Question about correct opened file
by ope 14 Feb '08

14 Feb '08

Hi, I've the following code: namespace io = boost::iostreams; bool foo::open( const std::string& file ) { io::filtering_istream is; is.push( my_line_filter() ); is.push( io::file_source( file ) ); // ??? how to check success do { std::string line; std::getline(is, line); std::cout << line << std::endl; } while (!is.eof()); return true; } Well, how can I check that the file is opened correct/the stream is valid? is_open() and good() seems not supported? Or I'm wrong? Giving a wrong name does nothings. Thanks, Olaf

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