May 2011 - Boost-users - lists.boost.org

Re: [Boost-users] Thread Safety of shared_ptr
by 乔志强 03 May '11

03 May '11

shared_ptr< Session >* sp_Session = new shared_ptr< Session >( new Session ); shared_ptr< Session >* is not a shared ptr, it is a RAW ptr to shared_ptr< Session>. So you should: 1. use shared_ptr of shared_ptr: shared_ptr<shared_ptr< Session > > sp_Session ( new shared_ptr< Session >( new Session )) ; 2. or use shared_ptr directly: shared_ptr< Session > sp_Session( new Session ); I think you should use 2. > ------------------------------ > > Message: 7 > Date: Tue, 3 May 2011 10:46:39 +1000 > From: "Kevin Frey" <kfrey(a)hardcat.com> > To: <boost-users(a)lists.boost.org> > Subject: Re: [Boost-users] Thread Safety of shared_ptr > Message-ID: > <95C19A2ED65BF54CB79DF1F9D6A488E0013E3351(a)hcmail1.MEL01.hardcat.com.a > u> > > Content-Type: text/plain; charset="us-ascii" > > > Actually, I am not sure with this statement. Destructor is only called > if shared count reaches zero. I don't think that this can happen, that a > dtor is called in one thread and the other thread is still able to > increment the shared count even from the weak_ptr. I remember reading > weak_ptr's source and saw that it is also protected again such a case. > > > > I have taken the example at face value, but in hindsight the examples > could be a lot better because there is no context to describe the > circumstances of how the shared_ptrs are instantiated. > > > > For example, is p allocated globally, and p2 & p3 allocated at the > beginning of their respective threads? If so, example 4 becomes > meaningless because Thread B cannot force p2 out of scope since it would > only go out of scope once thread A exits, since thread A controls the > scope of p2. If thread B were to force p2 "out of scope" then p2 would > have to be a shared_ptr< >*, dynamically allocated., and subsequently > deleted by Thread B. But it is not represented that way. > > > > Unfortunately none of this helps solve my original question, which given > the direction this thread is proceeding, I will re-state in pseudo-code > that approximates the *actual* situation occurring in my program: > > > > Earlier on: > > > > shared_ptr< Session >* sp_Session = new shared_ptr< Session >( new > Session ); > > > > Dependent_Class* dep = new Dependent_Class( shared_ptr< Session >& > shared_ptr_session ); > > In Dependent_Object::Dependent_Object( ) > > this->sp_Session = new shared_ptr< Session >( shared_ptr_session ); > > Now, simultaneously: > > > > Thread A: > > Dependent_Class* dep2 = new Dependent_Class( shared_ptr< Session>& > shared_ptr_session ); > > In Dependent_Object::Dependent_Object( ) > > this->sp_Session = new shared_ptr< Session >( shared_ptr_session ); > > > > Thread B: > > In Dependent_Class::~Dependent_Class( ): // the cleanup of dep > > delete this->sp_Session; > > > > So, we have: > > > > 1. A shared object (pointed to by a shared_ptr) that is presently > in existence with a reference count of at least 2. > > 2. One thread A creating another shared_ptr to the shared object, > attempting to increment the reference count. > > 3. Another thread B simultaneously destroying a *different* > shared_ptr which is connected to the same underlying shared object, > decrementing the reference count. > > > > Note that the shared object is *not being destroyed* here, just the > reference counts are being manipulated. > > > > Will shared_ptr handle this situation correctly? > > > > Thanks > > > > Kevin > > >

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boost as shared library - linux
by Krzysztof 02 May '11

02 May '11

When I try to use libboost_program_options.so in my program it gives me a message: error while loading shared libraries: libboost_program_options.so.1.46.1: cannot open shared object file: No such file or directory I tried to do the command "ldconfig -n" and substitute to LD_LIBRARY_PATH the dir where it is located - the message remains the same. The boost library directory is in my home folder. How to overcome this? -- Regards Krzysztof J.

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[Test] Compiling libraries for Windows Mobile 6 ARMV4I
by Paul Heil 02 May '11

02 May '11

I would like to be able to use the Boost.Test library for Windows Mobile 6 ARMV4I projects compiled by Visual Studio 2008. I can successfully compile the Boost.Signals, Boost.Thread, Boost.System, and Boost.Random libraries; but Boost.Test uses several functions that aren't available under Windows Mobile even with STLPort 5.2.1. Specifically, these are strerror() and getenv(). The actual compile errors I receive are: /test/impl/cpp_main.ipp(38) : error C2039: 'getenv' : is not a member of '`global namespace'' /test/impl/cpp_main.ipp(38) : error C2873: 'getenv' : symbol cannot be used in a using-declaration /test/impl/cpp_main.ipp(38) : error C2039: 'strerror' : is not a member of '`global namespace'' /test/impl/cpp_main.ipp(38) : error C2873: 'strerror' : symbol cannot be used in a using-declaration /test/impl/execution_monitor.ipp(1306) : error C2039: 'strerror' : is not a member of 'stlpd_std' /test/impl/execution_monitor.ipp(1306) : error C3861: 'strerror': identifier not found /test/impl/cpp_main.ipp(106) : error C2039: 'getenv' : is not a member of 'stlp_std' /test/impl/cpp_main.ipp(106) : error C3861: 'getenv': identifier not found I have seen past postings by other users that have suggested they have supplemented STLPort with these functions (particularly posts relating to VeetoFTC), but I have yet to see an actual example of the code changes necessary to do that. Can anybody suggest the least intrusive way to add this functionality so that I can compile the rest of Boost? Thanks, PaulH

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[phoenix] conditional expression?
by alfC 02 May '11

02 May '11

Hi, Does Phoenix support conditional expression? I know if supports if_ *statements* but it seems that there's is no conditional (expression*. The question what is is the equivalent for "(x>2.)?(1.):(-1.)" in general. For example, I tryed with if_[].else_[] hoping that the statement is used as result but with no luck: #include<boost/phoenix/phoenix.hpp> #include<iostream> using namespace boost::phoenix; using namespace boost::phoenix::arg_names; int main(){ std::clog << (arg1*arg1)(2.) << std::endl; //returns correctly 4 std::clog << (if_(arg1>2.)[val(1.)].else_[val(-1.)])(2.) << std::endl; //syntax error return 0; } The syntax error points that the expression fails to evaluate as a number. Any ideas? -- Thanks, Alfredo usr/include/boost/proto/operators.hpp:79:9: error: forming reference to void if.cpp:8:43: error: no match for ‘operator<<’ in ‘std::clog << boost::phoenix::if_ [with Cond = boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tag::greater, boost::proto::argsns_::list2<boost::phoenix::actor<boost ... etc, etc, 100 lines

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[iostreams] Flushing problems with :filtering_ostream
by Bo Jensen 02 May '11

02 May '11

I had some older code which used to work before, but seem to have flushing problems now. The problem is I can not make boost::iostreams::filtering_ostream flush properly. Here is a snippet of my code, which is not compilable in the current form, since I just pulled it out of my own code. Here it goes : /* Helper class for writing gzipped files */ class gzip_sink { public: typedef char char_type; typedef boost::iostreams::sink_tag category; Log &Logger_; /* Logger */ boost::iostreams::filtering_ostream sink_; /* Sink used to push filters */ SlmOfstream outifstr_; /* Write stream to be pushed into sink */ std::wstring name_; /* Store name of attached file */ /* Constructor */ gzip_sink(const wchar_t *filename,Log &logger) SlmExcStartConstructor : Logger_(logger), name_(filename) { /* Open for write */ SlmOpenWriteFile(Logger_, name_.c_str(), outifstr_); /* Push gzip compressor */ sink_.push(boost::iostreams::gzip_compressor()); } SlmExcStopConstructor gzip_sink(const gzip_sink &rhs) SlmExcStartConstructor : Logger_(rhs.Logger_), name_(rhs.name_) { /* Open for write */ SlmOpenWriteFile(Logger_, name_.c_str(), outifstr_); /* Push gzip compressor */ sink_.push(boost::iostreams::gzip_compressor()); } SlmExcStopConstructor void Close() { sink_.reset(); } ~gzip_sink() { sink_.reset(); } /* Write function */ std::streamsize write( const char * s, std::streamsize n ) { /* Push write stream */ /* THIS IS THE HACK !!! WE NEED TO PUSH AND POP EACH TIME OTHERWISE SOME FLUSH IS NOT DONE!! */ sink_.push(outifstr_); sink_.write(s,n); sink_.pop(); return n; } }; I have to push and pop the stream on to the sink each time I write, which should only be done once in the constructor. It is clearly some flushing issue, but I have tried flushing in all places and no luck, any help ? If you think it looks a bit odd, it's because I use it together with boost::iostreams::code_converter<gzip_sink> to be able to use gzip with wide streams.

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[Review] Boost.Convert library, last day
by Edward Diener 02 May '11

02 May '11

This is a reminder that formal review of the Boost.Convert library by Vladimir Batov ends today, May 2. There have only been a few reviews of the library so the library welcomes reviews. If you are one of the people who have been dissatisfied by the perceived limitations of Boost lexical_cast, or have discussed such limitations on Boost mailing lists in the past, please look at the library and give a review of it, as its intent is to offer a greatly enhanced version of lexical_cast as a new library. *************** * Its Purpose * *************** The library builds on the past boost::lexical_cast experience, then takes those conversion-related ideas further to suit better today's applications and programing needs. It still offers simple, minimal interface, familiar conversion behavior and additionally provides: * throwing and non-throwing conversion-failure behavior; * support for the default/fallback value to be returned when conversion fails; * two types of the conversion-failure check - basic/simple and better/safe; * formatting support based on the standard std::streams and std::stream-based manipulators (like std::hex, std::scientific, etc.); * support for different locales; * support for boost::range-compliant char and wchar_t-based containers; * no DefaultConstructibility requirement for the Target/Destination type; * consistent framework to uniformly incorporate any type-to-type conversions, extensibility and additional room to grow. With its present support for string-to-type and type-to-string conversions it is an essential tool for applications making extensive use of configuration or MS-Windows-Registry-style files or having to process/prepare considerable amounts of data in, say, XML, etc. More so, it is easily extendable to accommodate, specialize and uniformly deploy new user-defined type-to-type conversions. ******************* * Where to get it * ******************* The Boost Vault is accesible again after being down for most of the week, so you can get the library from the Boost Vault at http://www.boostpro.com/vault/index.php?action=downloadfile&filename=boost-… You can also get the library, using Subversion, from https://svn.boost.org/svn/boost/sandbox/convert. The HTML documentation is part of the distribution and can be found at libs/convert/index.html in the distribution above. ******************** * Writing a review * ******************** The reviews and all comments should be submitted to the developers list, and the email should have "[convert] Review" at the beginning of the subject line to make sure it's not missed. Please explicitly state in your review whether the library should be accepted. The general review checklist: - 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? And finally, every review should answer this question: - Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion. Edward Diener, Review Manager

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Re: [Boost-users] [Multi-Index] Categorised Container
by Hossein Haeri 02 May '11

02 May '11

Hi Joaquín, > multi_index_conainer< > T, > ordered_non_unique< > composite_key< > T, > member<T,category_t,&T::category>, > member<T,second_type,&T::second> > > > >, > ordered_non_unique<...> > > my_container; > > Now, if you do an equal_range on a category elements will indeed be > sorted by the second member. Right. Here is a better formulated question then: Let's say c1 is an object of type category_t. When I apply equal_range for c1, will I get my desired range in log(n) time (where n == my_container.size())? Or, will I get it in O(1) for the elements are already stored in a category-by-category manner? TIA, --Hossein

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Fwd: Re: [Review] Boost.Convert library, last 3 days
by Edward Diener 01 May '11

01 May '11

I am forwarding this message sent directly to me as the review manager of the Boost Convert library review. I have removed the forwarding information to protect privacy. Hi Edward, I am by no means an expert in library design, so perhaps I have a few comments from the user-only perpective: > - What is your evaluation of the design? I think the design is appropiate in terms of purely extending lexical_cast in terms of fallback values and optional exceptions. However, I was expecting more from a library that extends on lexical_cast, for example in terms of one of the goals of the library, which is compact syntax. The feature I was expecting was conversion based on default casting. In the library it seems that the source type can be omitted (just as in lexical_cast). I would be a desired feature that also destination types could be omitted. This could be possible using cast operator such that Destination d = auto_convert::from(s); // or convert<>::from(s) // default template parameter interpreted as potential auto conversion based on destination type. Instead of the redundant Destination d = convert<Destination>::from(s); I think the requested feature (unless it is not possible, in that case I am sorry about my request) is to be expected from the library. > - What is your evaluation of the implementation? I have no comments on it since I wouldn't be able to judge on implementation used. > - What is your evaluation of the documentation? The documentation is understandable and appropriate. > - What is your evaluation of the potential usefulness of the > library? I would use the library just based in considering the natural and explicit syntax introduced. Even more if the requested feature above is introduced. > - Did you try to use the library? With what compiler? Did you > have any problems? no > - How much effort did you put into your evaluation? A glance? A > quick reading? In-depth study? A glance > - Are you knowledgeable about the problem domain? no. Only from the point of view convenience. > - Do you think the library should be accepted as a Boost library? yes, I think it should be accepted. I hope this quick review is useful to make a decision. Although the validity and weight of my vote can be objected because I am not really an active player of the Boost community. Thank you, Alfredo Correa

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[Spirit] Semantic actions (binary parser) - user error or bug?
by Vitaly Budovski 01 May '11

01 May '11

Hi, I've come across some behaviour with semantic actions that seems strange. I'm not sure if this is intended or if it is indeed a bug. Please see the attached test case.

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