September 2006 - Boost-users - lists.preview.boost.org

Re: [Boost-users] Library Interface Design
by Sohail Somani 18 Sep '06

18 Sep '06

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of > Robert Kindred > I can think of one example for not fully constructing objects: [snip] > The problem is in starting up. If each one of these threads > knows about > each other via some method (pointer, or reference), then when > a thread > starts up its own business, whatever that is, then most > likely it will start > generating data and sending messages. When it tries to send > a message to a > thread that does not yet exist, BOOM!!! (yes, I have > experienced this boom). Can you not create them all, have them wait on some condition variable and signal when you're ready to go?

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Re: [Boost-users] Boost serialization : concurrency
by Moshe Matitya 18 Sep '06

18 Sep '06

Daniel F. Savarese wrote: > ... > However, I think I have a workaround that I just finished > testing (at least the unit tests no longer seg fault). > If you're willing to waste some memory and add the equivalent > of the following to oserializer > > private: > static oserializer & dummy; > > static oserializer & _instantiate(){ > static oserializer instance; > return instance; > } > public: > static oserializer & instantiate(){ > return dummy; > } > > and to iserializer: > > private: > static iserializer & dummy; > > static iserializer & _instantiate(){ > static iserializer instance; > return instance; > } > public: > static iserializer & instantiate(){ > return dummy; > } > > and initialize oserializer::dummy as: > template<class Archive, class T> oserializer<Archive,T> & > oserializer<Archive,T>::dummy = > oserializer<Archive,T>::_instantiate(); > > and iserializer::dummy as: > template<class Archive, class T> iserializer<Archive,T> & > iserializer<Archive,T>::dummy = > iserializer<Archive,T>::_instantiate(); > > then the local static will be initialized at program initialization > before any threads are running without incurring the global variable > initialization ordering problem. > ... > This is just a test hack, but I think the concept works. Sorry, I don't think your idea works: (1) What happens if the constructor or initializer of a global or static member variable calls oserializer::instantiate(), and that variable is initialized before oserializer::dummy is initialized? E.g.: struct foo { foo() { // oserializer::dummy might not be initialized yet, // so this can return a reference to an invalid object: oserializer<x,y> os = oserializer::instantiate(); os.do_something(); // boom } }; foo g_f; (2) There exists no guarantee that multiple threads will not be running at program initialization time. Threads can be started in the constructors and initializers of global or static member variables. E.g.: void thread_func() { // oserializer::dummy might not be initialized yet, // so this can return a reference to an invalid object: oserializer<x,y> os = oserializer::instantiate(); os.do_something(); // boom again } struct bar { bar() { boost::thread t(&thread_func); } } bar g_b; (Btw, if your idea really did work, then you would have just invented a thread-safe implementation of the Singleton pattern that does not require any thread synchronization. I don't believe that's possible.) Moshe

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[Boost.Signal] Single-shot Connection?
by Wu Yinghui, Freddie 18 Sep '06

18 Sep '06

Dear all, I sent in this on 14 Sept, but have received no reply so far. As I'm not sure if it was lost in the void, I'm resend the mail again. Please bear with me if you have received the same question before. > I'm a happy user of Boost.Signal, as it brings great power to our > software design in terms of loosening all the coupling between > components. > > However, I recently come across a case where a single-shot slot is > desired (i.e., a signal-slot connection that is automatically > disconnected once the signal is invoked for once). In our current > implementation, we have to keep boost::signals::connection object around > with the slot implementation, so that it can disconnect it after the first invocation. > > However, we have this problem of boost::signals::connection management, > since one signal may be connected to different signals and we have > problem identifying the correct connection to be disconnected. So my > question is: Is there any easier way (i.e., ways that doesn't involve > the implementation of the slot function itself) that I can add a > single-shot signal-slot connection? > > Any suggestion is appreciated. Cheers, Freddie -- Wu Yinghui, Freddie Research & Development Senior Software Engineer Volume Interactions Pte Ltd 1 Kim Seng Promenade, #12-01 Great World City East Tower Singapore 237994 Tel: +65 62226962 (Ext 216) Fax: +65 62226215 Email: yhwu(a)volumeinteractions.com URL: http://www.volumeinteractions.com Important: This message is intended for the recipient(s) addressed above. It contains privileged and confidential information. If you are not the intended recipient, please notify the sender immediately by replying to this message and then delete it from your system. You must not read, copy, use, or disseminate this communication in any form. Thank you.

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Re: [Boost-users] Boost serialization : concurrency (was Possibletoappend...)
by Robert Ramey 18 Sep '06

18 Sep '06

Hmmm - well that is interesting. I believe I used this idiom in order to address a problem where global static variables couldn't be guarenteed to be instantiated in a particular order and this was the fix recommended. So now what do we do? Robert Ramey Daniel F. Savarese wrote: > In message <eek3v5$hbk$1(a)sea.gmane.org>, "Robert Ramey" writes: >> So now you know my intention - and I believe that the code reflects >> that. > > Here's what's happening with > static oserializer & instantiate(){ > static oserializer instance; > return instance; > } > Thread 1 calls instantiate and is pre-empted in the middle of > constructing instance the first time control passes through its > declaration. Thread 2 then calls instantiate and returns a > reference to an incompletely constructed instance. Then thread 2 > bombs in basic_oarchive_impl::save_object the first time it tries to > dereference the object to invoke a virtual function > (in this case class_info()) of an incompletely constructed object > (i.e., no virtual function table). And now I'm reminded why whenever > I see a static local variable I have the knee-jerk reaction: > "not thread-safe." I had to reeducate myself by exercising the > debugger and revisiting what the C++ standard has to say about > the initialization of static storage. > > daniel > > -#-#-#-#-| Sleep and The Traveller |-#-#-#-#-#-#-#- > http://www.savarese.org/ In distant lands, I hear the call of my > home. # s a v a r e s e > Yet my work is not done. My journey's just begun.- software > research -- http://www.sleepandthetraveller.com/ # > http://www.savarese.com/

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[boost::serialization]: Dies with access violation (segfaults) reading beyond the end of archive.
by Konstantin Andreev 18 Sep '06

18 Sep '06

When 1) trying to restore from archive the pointer to sample class, and 2) archive is over at this moment boost::serialization causes Access Violation Fault in file: basic_iarchive.cpp, line 470: bpis_ptr = co.bpis_ptr; The code to reproduce the fault follows. -- Konstantin Andreev. ------------------------( cut here )---------------------- #include <iostream> #include <sstream> #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> class Sample { private: int pod_int; std::string pod_str; template<class Archive> void serialize(Archive & ar, const unsigned int ){ ar & pod_int & pod_str; }; friend class boost::serialization::access; friend std::ostream & operator<<(std::ostream & os, const Sample & sa ); public: Sample() {}; Sample( int _i, std::string _s ) : pod_int( _i), pod_str( _s ) {}; }; BOOST_CLASS_TRACKING(Sample, track_never) BOOST_CLASS_VERSION(Sample, 19) std::ostream & operator<<(std::ostream & os, const Sample & sa ) { return os << "-- int: " << sa.pod_int << ", str: >" << sa.pod_str << "< at 0x " << &sa << '\n'; } int main( void ) { Sample *obj_to = NULL; const Sample * const obj_fr = new Sample( 55, "**** test string *****" ); std::cout << *obj_fr; std::stringstream archbuf; boost::archive::text_oarchive *oa = new boost::archive::text_oarchive( archbuf, 3 ); *oa << obj_fr; std::cout << "-- archive content: >" << archbuf.str() << "<\n"; delete oa; boost::archive::text_iarchive *ia = new boost::archive::text_iarchive( archbuf, 3 ); *ia >> obj_to; std::cout << *obj_to; /////////////////////////////////// *ia >> obj_to; // ARCHIVE IS OVER. BOOM !!! /////////////////////////////////// std::cout << *obj_to; delete ia; return 0; }

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[serialization] serialization of pointers to primitive types?
by Joaquín Mª López Muñoz 17 Sep '06

17 Sep '06

The following test program: #include <boost/archive/text_oarchive.hpp> #include <sstream> int main() { int x=0; int* const px=&x; std::ostringstream oss; boost::archive::text_oarchive oa(oss); oa<<px; return 0; } produces this error in MSVC++ 6.0: ...boost/serialization/access.hpp(109) : error C2228: left of '.serialize' must have class/struct/union type ...boost/serialization/serialization.hpp(81) : see reference to function template instantiation 'void __cdecl boost::serialization::access::serialize( class boost::archive::text_oarchive &,int &,const unsigned int)' being compiled and the following error in GCC 3.2: ...boost/serialization/access.hpp: In static member function `static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = int]': ... ...boost/serialization/access.hpp:109: request for member `serialize' in `t', which is of non-aggregate type `int' I've checked the same snippet against Boost 1.33.1, CVS HEAD and RC_1_34_0, using other primitive types like std::string, same problem always. Same problem also for the loading counterpart. When the pointed-to type is not primitive, though, everything works fine, regardless of whether the type has intrusive or non intrusive serialization support. I am sure I'm doing something really stupid here, but I've been banging my head against this several hours. Some clue greatly appreciated. Thank you, Joaquín Mª López Muñoz Telefónica, Investigación y Desarrollo

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[timer] Comments do not match the implementation?
by KSpam 17 Sep '06

17 Sep '06

I would like to use boost::timer to replace a timing object from another library. In looking into the header file, I noticed the following comments: // It is recommended that implementations measure wall clock rather than CPU // time since the intended use is performance measurement on systems where // total elapsed time is more important than just process or CPU time. All is well and good I thought to myself ... wall clock is exactly what I want! But alas, the implementation just wraps std::clock(). The man page for clock states the following: "The clock() function returns an approximation of processor time used by the program." In summary, the header states that the timer implementation should use wall clock time, but it ignores its own advice and uses processor time. I'm confused. Do I need to create my own timer implementation in order to use wall clock time? Thanks, Justin

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Re: [Boost-users] Boost serialization : concurrency (was Possibleto append...)
by Robert Ramey 17 Sep '06

17 Sep '06

So now you know my intention - and I believe that the code reflects that. I'm guessing that the key might be that the DLL gets unloaded "too soon" so that we get a seg fault by invoking code that is no longer in memory. But as you have discovered - this is very problematic to track down and could be a subtle error of my own, an error in the language support system (loading/unloading DLLS). Overzealous optimization on the compiler's part or something else entirely. Sorry I can't be of more help. Good Luck Robert Ramey

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[asio] Strange compilation error
by Christian Henning 17 Sep '06

17 Sep '06

Hi there I'm experiencing a strange compilation error that I cannot resolve myself. The following non-functionating triggers the error. I'm using VC2003 SP1. The error is due to the write() call. template <class T > void sent( const T& object ) { std::ostringstream archive_stream; boost::archive::binary_oarchive archive( archive_stream ); archive & object; std::string outbound_data = archive_stream.str(); // Format the header. std::ostringstream header_stream; header_stream << std::setw( 8 ) << std::hex << outbound_data.size(); std::string outbound_header = header_stream.str(); // Write the serialized data to the socket. We use "gather-write" to send // both the header and the data in a single write operation. std::vector<boost::asio::const_buffer> buffers; buffers.push_back(boost::asio::buffer(outbound_header)); buffers.push_back(boost::asio::buffer(outbound_data)); boost::asio::write( socket, buffers ); } This is the verbose error message: ..\..\..\External\Includes\Boost\asio\impl\write.ipp(40) : error C2825: 'Sync_Write_Stream::error_type': cannot form a qualified name ..\..\..\External\Includes\Boost\asio\impl\write.ipp(58) : see reference to function template instantiation 'size_t boost::asio::write<Sync_Write_Stream,Const_Buffers,boost::asio::detail::transfer_all_t,boost::asio::detail::throw_error_t>(Sync_Write_Stream (__stdcall &),const Const_Buffers &,Completion_Condition,Error_Handler)' being compiled with [ Sync_Write_Stream=SOCKET (int,int,int), Const_Buffers=std::vector<boost::asio::const_buffer>, Completion_Condition=boost::asio::detail::transfer_all_t, Error_Handler=boost::asio::detail::throw_error_t ] SendImages.cpp(75) : see reference to function template instantiation 'size_t boost::asio::write<SOCKET(int,int,int),std::vector<_Ty>>(Sync_Write_Stream (__stdcall &),const Const_Buffers &)' being compiled with [ _Ty=boost::asio::const_buffer, Sync_Write_Stream=SOCKET (int,int,int), Const_Buffers=std::vector<boost::asio::const_buffer> ] ..\..\..\External\Includes\Boost\asio\impl\write.ipp(40) : error C2039: 'error_type' : is not a member of 'operator``global namespace''' ..\..\..\External\Includes\Boost\asio\impl\write.ipp(40) : error C2146: syntax error : missing ';' before identifier 'e' ..\..\..\External\Includes\Boost\asio\impl\write.ipp(40) : error C2065: 'e' : undeclared identifier ..\..\..\External\Includes\Boost\asio\impl\write.ipp(41) : error C2228: left of '.write_some' must have class/struct/union type type is '__w64 unsigned int (__stdcall &)(int,int,int)' ..\..\..\External\Includes\Boost\asio\impl\write.ipp(41) : error C3861: 'e': identifier not found, even with argument-dependent lookup ..\..\..\External\Includes\Boost\asio\impl\write.ipp(44) : error C3861: 'e': identifier not found, even with argument-dependent lookup ..\..\..\External\Includes\Boost\asio\impl\write.ipp(46) : error C3861: 'e': identifier not found, even with argument-dependent lookup ..\..\..\External\Includes\Boost\asio\impl\write.ipp(50) : error C2825: 'Sync_Write_Stream::error_type': cannot form a qualified name ..\..\..\External\Includes\Boost\asio\impl\write.ipp(50) : error C2039: 'error_type' : is not a member of 'operator``global namespace''' ..\..\..\External\Includes\Boost\asio\impl\write.ipp(50) : error C2146: syntax error : missing ';' before identifier 'e' ..\..\..\External\Includes\Boost\asio\impl\write.ipp(50) : error C3861: 'e': identifier not found, even with argument-dependent lookup ..\..\..\External\Includes\Boost\asio\impl\write.ipp(51) : error C3861: 'e': identifier not found, even with argument-dependent lookup Thanks ahead, Christian

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Need help with boost and dev-c++
by Craig Ritzdorf 17 Sep '06

17 Sep '06

I'm having a problem using any part of boost in dev-c++. The compiler itself seems to handle the code fine but when it trys to link i get the error: [Linker error] undefined reference to 'boost::filesystem::path::path(char const*)' I looked through the archive and found someone else (Chun Ping Wang) with this same problem but it was never answered. Thanks Craig

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