December 2008 - Boost - lists.preview.boost.org

[Function] Problem using target() with boost::mem_fn and boost::bind
by Pengcheng Song 03 Dec '08

03 Dec '08

Hi, I have encountered a crash trying to use the target() function to retrieve a function pointer from a boost.function initialized with a member function (using boost.bind). See the code below. // =========================================== #include <iostream> #include <boost/bind.hpp> #include <boost/function.hpp> typedef double(*FunctionType) (double); double Square( FunctionType f, double x ) { return f(x) * f(x) ; } class A { private: double x_; double y_; public: A() : x_(1.0), y_(1.0) {} double Area(double x, double y) { x_ = x; y_ = y; return x_ * y_; } }; int main() { A a1; boost::function<double(double)> f1 = boost::bind( boost::mem_fn(&A::Area), &a1, _1, 2.5 ); double s1 = f1(2.0); // this works FunctionType f2 = *f1.target<FunctionType>() ; // Error: this would crash s1 = Square( f2, 2.0 ); return 0; } // ====================================================== After debugging the code, I found out that the crashed happened inside target() function in file function_base.hpp: template<typename Functor> Functor* target() { if (!vtable) return 0; detail::function::function_buffer type_result; type_result.const_obj_ptr = &typeid(Functor); vtable->manager(functor, type_result, detail::function::check_functor_type_tag); return static_cast<Functor*>(type_result.obj_ptr); } After vtable->manager() call, type_result became null, and this caused static_cast to fail. I was using boost_1_36_0 precompiled by BoostPro with Visual Studio 2008. Is this an expected behavior? Your feedback would be greatly appreciated. Pengcheng Song -- View this message in context: http://www.nabble.com/-Function--Problem-using-target%28%29-with-boost%3A%3… Sent from the Boost - Dev mailing list archive at Nabble.com.

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[python] Bug during build process?
by Robert Dailey 03 Dec '08

03 Dec '08

Hi, I execute the following command to build the entire boost 1.37 library with python debugging ON: *bjam --toolset=msvc --layout=system link=shared threading=multi variant=debug python-debugging=on stage* I then use dependency walker <http://www.dependencywalker.com/> to load the file *boost_python-mt-gyd.dll* and I see that both python25.dll and python25_d.dll are being loaded side by side. This obviously shouldn't be happening and only python25_d.dll should be loaded. Is there a bug in the build script for boost python, or am I doing something wrong?

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[inteprocess] maximum length for names of mutexes, memory segments etc.
by JOAQUIN M. LOPEZ MUÑOZ 03 Dec '08

03 Dec '08

Boost.Flyweight uses long names for some internal mutexes and memory segments inside the intermodule_holder component, with the purpose of guaranteeing name unicity. For instance, this is a typical name for such an internal mutex, with length 87: boost_flyweight_intermodule_holder_mutex_5660_601342046_2913549788_3054690985_591945496 However, on some platforms line NetBSD 87 chars is too much:

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[future N2561] Implementation comments
by vicente.botet 03 Dec '08

03 Dec '08

Hi, on the current Future (N2561) library proposal the promise protect the value setting/getting from multiple threads using a lock, but the lock do not protect the future initialization (lazy_init()). void set_value(typename detail::future_traits<R>::source_reference_type r) { lazy_init(); boost::lock_guard<boost::mutex> lock(future->mutex); if(future->done) { throw promise_already_satisfied(); } future->mark_finished_with_result_internal(r); } I'm wondering if we don't need to extend the protection or avoid the lazy initialization? I'm missing something? BTW, Is it safe to take the address of a promise? If not, why not delete the operator&()? Best, Vicente

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[xpressive] regex_token_iterator - bug, feature, misunderstanding query?
by Michael Goldshteyn 03 Dec '08

03 Dec '08

OK, so I want to use the sregex_token_iterator functionality to split a data string. The data string contains: /a/b//c/ The delimiter is the forward slash and I do want empty strings. I expect to get: {}{a}{b}{}{c}{} What I actually get is: {}{a}{b}{}{c} The empty string after {c}, which I expect because the data string ended in a forward slash, is missing. What do I have to do to get the empty string after {c} if the data string ends in a forward slash? The code is as follows: --- #include <iostream> #include <string> #include <boost/xpressive/xpressive.hpp> #include <boost/xpressive/regex_token_iterator.hpp> int main(int argc, char *argv[]) { // Split the path using namespace boost::xpressive; // For simplicity sregex levelSplitter(as_xpr('/')); std::string nodePath("/a/b//c/"); sregex_token_iterator begin(nodePath.begin(),nodePath.end(),levelSplitter,-1); sregex_token_iterator end; for (sregex_token_iterator iCur=begin;iCur!=end;++iCur) std::cout << '{' << *iCur << '}'; std::cout << std::endl; return 0; } --- Thanks, Michael Goldshteyn

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Re: [boost] [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today
by Mika Heiskanen 03 Dec '08

03 Dec '08

Mathias Gaunard wrote: > I say it is up to the programmer to ensure valid values are provided. > If the value is only known at runtime, there should be explicit checking > in the code prior to assignment. If the value must be checked beforehand, why bother using a constrained type at all? Where's the benefit if all assignments are already guaranteed to be valid by external tests? Might just as well use a test+POD combination. --> Mika Heiskanen

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How to access the Boost wiki?
by vicente.botet 03 Dec '08

03 Dec '08

Hi, In order to access the Boost wiki I do COMMUNITY > Requesting a New Feature > " ticket system," > Wiki. Is there a shorter way? If not can we add it on COMMUNITY? Best, Vicente

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Which Future library will be reviewed?
by vicente.botet 03 Dec '08

03 Dec '08

Hi Anthony, your current Boost.Future(http://www.justsoftwaresolutions.co.uk/files/n2561_future.hpp + http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2561.html) library is closer to the C++0x standard than the Boost.Future from Braddock. This let me think that yours is a better candidate for Boost, but the current state of your library interface has some differences, restrictions and extensions respect to the standard http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2627.html and http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2709.html I know that you have implemented a prototype for an earlier version of n2676 available at http://www.justsoftwaresolutions.co.uk/threading/updated-implementation-of-…. I would like to know which one will be reviewed? Do you plan to review your current Boost proposal and adapt it to the current C++0x proposal before the review. IMO, if you do that the review will be much more efficient. The current documentation includes often the C++0x interface and not the C++98 emulation. Do you plan to add it? before the review? In addition to the current reference, do you plan to add more documentation such as tutotial, examples, design rationale, implementation notes? before the review? I think restrictions/extensions to the standard should be stated explicitly. A comparaison of your implementation and the standard seems mandatory. * How move semantics is emulated (restrictions) * How the default constructed deleted functions are emulated (note that these are part of the interface) Next follows some differences that need attention (from http://www.justsoftwaresolutions.co.uk/files/n2561_future.hpp) ===== private: unique_future& operator=(unique_future& rhs);// = delete; versus public: unique_future& operator=(const unique_future& rhs) = delete; ===== wait_for, wait_until versus timed_wait, timed_wait_until ===== shared_future & operator=(const shared_future& rhs) = delete; versus shared_future& operator=(shared_future const& other); === shared_future(const shared_future& rhs); shared_future(unique_future<R>); shared_future(); shared_future & operator=(const shared_future& rhs) = delete; Versus shared_future(); ~shared_future(); // copy support shared_future(shared_future const& other); shared_future& operator=(shared_future const& other); ===== template<class> class packaged_task; // undefined template<class R, class... ArgTypes> class packaged_task<R(ArgTypes...)> { public: typedef R result_type; versus template<typename R> class packaged_task { HTH for the review, Vicente

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[announce][flyweight] Boost.Flyweight added to the trunk
by JOAQUIN M. LOPEZ MUÑOZ 02 Dec '08

02 Dec '08

Hello, I'm happy to announce that Boost.Flyweight has been just commited to the SVN trunk, far too many months later than initially planned (but better later than never). The goal is to have the lib included in Boost 1.38, if its stability and the release manager permit. If you're interested in the Boost.Flyweight please update your SVN copy, play with the lib and report your comments/complaints. Thank you, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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Re: [boost] [Review] UUID library (mini-)review starts today, November 23rd
by Vladimir.Batov＠wrsa.com.au 02 Dec '08

02 Dec '08

Andy, >> ... > > The first thing that comes to mind is size. A uuid class that holds the > data at text ... > As a much more minor note, ... I thought you might jump on my mikki-mouse string-based UUID... and in fact it was a trap of a sort. :-) I had a strong impression that the discussion in this thread revolved too much about actual implementation (MAC retrieval springs to mind) and too little about the interface. Yes, the implementation is important but it is the interface that makes it or breaks it as far as user's acceptance is concerned. That (acceptance) buys you time to improve the implementation hidden behind the interface. My concern with the proposal is that IMHO the interface has not been given enough consideration from the user perspectives. > I agree that many users do not care about the algorithm used. If they > really don't care, is it an issue to use the > boost::uuids::uuid_generator > since they don't really care what it does anyway? I feel that "do not care" is an oversimplification. The user does care -- he wants the "best available" without getting bogged down investigating what that "best available" exactly is. That is what Linux uuid_generate() gives the user right out of the box. To be successful boost::uuid just has to match that offer. > I believe they would > just use this function and assume all is well. I have to disagree. As a user I do not want to *assume*. I want to *know* that my application uses the available infrastructure to the fullest. That way if/when something goes wrong, it'll the OS to blame and not my application. > Those who care will look > at what boost::uuids::uuid_generator does and decide for themselves. Unfortunately, the reality begs for correction. I do care. However, with dead-lines approaching and the boss breathing down my neck I simply have no resources to look at every damn thing to decide for myself. In fact, I do not want to as I expect much-smarter-than-me people to have taken care of that for me. Exactly as I do not try reinventing std::map (even though I am aware of other than red-black-tree algorithms available). > They will likely be happy as long as there are the options that they > want. Giving options is merely part of the deal -- people often hate choice/options as they have to stop/think/evaluate/decide -- that process in time-consuming and draining, it distracts people from their main task. The only option pretty much guaranteed to succeed IMHO is the "best available" option. > I do want boost::uuid to provide algorithms to create uuids. I don't > want platforms that don't provide an algorithm to not be able to easily > create a uuid. Thus I don't want boost::uuid to be just a wrapper > around > OS functionality. I do not think I said I wanted to see boost::uuid to be just a wrapper. In a nut-shell I'd like to see boost::uuid providing the user with the "best available" option. If that means Linux uuid_generate() or your own algorithm under the hood, then it's fine by me. > > Does boost::uuid provide superior support and a upgrade path? >> ... > > I would agree, that boost::uuid will never have the support of > industrial/commercial scale. I now think that boost::uuid should > provide > a windows_uuid_generator (that uses UuidCreate), a linux_uuid_generator > (that uses uuid_generate), plus possibility others platform specific > ones, > plus some of it's own. Then a boost::uuids::uuid_generator could use > one of these if available and if not, use it's own generator. This > would > give users the support and upgrade paths that you are talking about. Makes a lot of sense to me. Saying to the user -- Dear user, I've done the hard yards for you and I've come up with the best option available on your platform -- is a lot. I believe the overwhelming majority will be very happy. The curious ones (or with too much time :-) on their hands) will still be able to play with explicit uuid generators via "uuid id(some-generator);" > ... > I do believe that a null uuid is a valid uuid, but regardless, if the > common use case really is as you say, then sure lets have the default > constructor call a function to generate a unique uuid. And still > provide a way to create a null uuid. Please do not take my word for it. Just look around at your own usage pattern of the default constructor beyond the UUID domain. > My work also heavily relies on uuids, but we almost never create one > ourselves in code. We get almost all our uuids from the database > that our program uses. Understood. Our usage is pretty much the same. Still, if my component does not create UUIDs, then IMHO it has to state that with Foo() : uuid_(boost::uuid::null()) // initially invalid {} That way the other poor soul coming after me won't be getting any wrong ideas/interpretations what the code is actually doing. > I would be surprised if there aren't many > others that use uuids in the same way, they receive them, they don't > generate them. Understood. I do not believe you should be providing the default constructor for that usage pattern -- it feels like the copy constructor is in order here. All in all my impression of the *current* situation with the proposal is that at *present* we have many useful and promising bits and pieces lying around. I see good ideas. I see good suggestions. I fail to see the product. It surely is a good start but to me we have not reached the destination yet. I'd be more comfortable after I see those bits and pieces taking shape. For me that shape primarily would be the interface and the documentation -- the initial pieces of the contract between the user and the implementor. Once both parties are happy with the contract, you'll beaver away providing the content/implementation. Thanks, Vladimir.

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