April 2009 - Boost-users - lists.preview.boost.org

[Fwd: io_service::strand - order of execution guarantees]
by Chris Hite 27 Apr '09

27 Apr '09

Can someone give me a guarantee about the order in which operations dispatched./posted to a strand are executed? Obviously if two different threads call post() or dispatch(), there is a race condition. However if one thread calls dispatch() twice, can it be sure that the first handler executes before the second? What happens if post() and dispatch() are mixed? Looking at the library it appears that a posted handler causes any subsequent dispatches to act exactly as posts. It appears as though a strong guarantee is being made: All handlers posted or dispatched will execute in order. If such a useful guarantee is required internally by asio, it should be made public and be documented. Christopher Hite RTS Realtime Systems Software GmbH, Rembrandtstrasse 13, D-60596 Frankfurt am Main T: +49.69.61009.0 / F: +49.69.61009.181 Sitz: Frankfurt am Main - HRB 84467 Amtsgericht Frankfurt am Main Geschäftsführer: Steffen Gemuenden, Igor Sluga www.rtsgroup.net This email and any attachments are for the exclusive and confidential use of the intended recipient. If you are not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, please do not read, distribute or take action in reliance upon this message. If you have received this in error, please notify me immediately by return email and promptly delete this message and its attachments from your computer system.

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[lambda] Return types in lambda expressions
by Michael Crawford 27 Apr '09

27 Apr '09

I'm trying to use bind and lambda to create a functor that can receive an event generated by my GUI library, and dispatch an appropriate event into a boost::statechart::state_machine. The GUI library requires the functor to have the signature bool (const CEGUI::EventArgs&). An example of what works: template<typename EventType> bool GuiEvent(const CEGUI::EventArgs&, GameStateMachine& gsm) { gsm.process_event(EventType( )); return true; } //usage: GameStateMachine sm; ... boost::bind(&GuiEvent<EventExitGame>, _1, boost::ref(sm)); But is it possible to use lambda to eliminate the need for the function? It looks like I would use something along the lines of boost::bind<bool>(boost::ref(sm).process_event(EventExitGame( )) /*somehow return true here*/, _1); I'm just not quite seeing how I would get the lambda expression to return true there. Cheers.

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Re: [Boost-users] undefined reference to `__sync_fetch_and_add_4'
by Birju Prajapati 27 Apr '09

27 Apr '09

I figured it out. It was an obscure, seemingly undocumented option to bjam: instruction-set=i686 i.e bjam architecture=x86 address-model=32 instruction-set=i686 --stagedir=stage32 --with-filesystem --with-thread --with-signals --with-serialization --with-system --with-program_options --with-date_time stage Could anyone point me to where I would have found that without grepping gcc.jam? From: Birju Prajapati Sent: 24 April 2009 13:12 To: boost-users(a)lists.boost.org Subject: undefined reference to `__sync_fetch_and_add_4' Hi, I built boost 1.38 as so: bjam architecture=x86 address-model=32 --stagedir=stage32 --with-filesystem --with-thread --with-signals --with-serialization --with-system --with-program_options --with-date_time stage Copied the files over to /usr/local/lib32: sudo cp stage32/lib/* /usr/local/lib32/ Compiled object files, eg: g++ -m32 -c -g -D_LINUX -I. -I/opt/sts_vendor/onix-eurex/include -I/usr/local/include/boost-1_38 -MMD -MP -MF build/Debug/GNU-Linux-x86/reference/ReferenceData.o.d -o build/Debug/GNU-Linux-x86/reference/ReferenceData.o reference/ReferenceData.cpp Then linking does not work: g++ -m32 -o dist/Debug/GNU-Linux-x86/spreadx build/Debug/GNU-Linux-x86/multicast/MulticastChannel.o build/Debug/GNU-Linux-x86/reference/ReferenceData.o build/Debug/GNU-Linux-x86/reference/Strategy.o build/Debug/GNU-Linux-x86/executor/MessageExecutor.o build/Debug/GNU-Linux-x86/multicast/MulticastSelector.o build/Debug/GNU-Linux-x86/fast/FIXStreamSubscriber.o build/Debug/GNU-Linux-x86/reference/Product.o build/Debug/GNU-Linux-x86/spreadx.o build/Debug/GNU-Linux-x86/fast/FIXMessage.o build/Debug/GNU-Linux-x86/multicast/Message.o build/Debug/GNU-Linux-x86/fast/FastDecoder.o build/Debug/GNU-Linux-x86/reference/Outright.o -L/opt/sts_vendor/onix-eurex/lib -L/usr/tibco/tibrv/lib -L/usr/local/lib32 -lffCppFixEngine -lACE -lcrypto -lboost_serialization-gcc43-mt -lboost_system-gcc43-mt -lboost_thread-gcc43-mt /usr/local/lib32/libboost_serialization-gcc43-mt.so: undefined reference to `__sync_fetch_and_add_4' I've tried #define BOOST_SP_USE_PTHREADS in user.hpp, I've tried -march=i486, but neither works. What gives? My platform details: birju@xx:~$ g++ --version g++ (Ubuntu 4.3.2-1ubuntu12) 4.3.2 Copyright (C) 2008 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. birju@xx:~$ uname -a Linux xx 2.6.27-11-generic #1 SMP Wed Apr 1 20:53:41 UTC 2009 x86_64 GNU/Linux birju@xx:~$ Cheers, Birju Schneider Trading 4th Floor, 25 Copthall Avenue London EC2R 7BP -------------------------------------------------------- Message from: Birju.Prajapati(a)schneidertrading.com Message to: boost-users(a)lists.boost.org Attached files: 0 This e-mail and any files transmitted with it are confidential, may be legally privileged, and are for the sole use of the intended recipient. Copyright in this e-mail and any accompanying document created by us is owned by us. If you are not the intended recipient of this e-mail or any part of it please telephone our IT Department at the number shown above or by e-mail at info(a)schneidertrading.com. You should not use or disclose to any other person the contents of this e-mail or its attachments (if any), nor take copies. This e-mail is not a representation or warranty and is not intended nor should it be taken to create any legal relations, contractual or otherwise. Schneider Trading Associates Ltd (Registration No. 3692131) is incorporated in England and Wales and the registered office is at 25 Copthall Avenue, London EC2R 7BP. The company is authorised and regulated by the Financial Services Authority

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[Statechart] Passing reference to create_processor()
by Hawkes Steve-FSH016 27 Apr '09

27 Apr '09

The Boost reference states that boost::ref can be used to pass an argument to statechart::fifo_scheduler::create_processor by reference instead of by value. I haven't been able to get this to work if the argument type derives from boost::noncopyable. It appears that the create_processor implementation instantiates code that attempts to copy the argument. Here's an example. Note that this compiles and runs sucessfully if Object does not derive from boost::noncopyable. Thanks, Steve Hawkes ---- #include <boost/statechart/asynchronous_state_machine.hpp> #include <boost/statechart/fifo_scheduler.hpp> #include <boost/statechart/simple_state.hpp> #include <boost/noncopyable.hpp> #include <boost/ref.hpp> #include <iostream> class Object : public boost::noncopyable { }; struct Initial; struct Test : boost::statechart::asynchronous_state_machine<Test, Initial> { public: Test(my_context ctx, Object& arg1) : my_base(ctx) { } }; struct Initial : boost::statechart::simple_state<Initial, Test> { }; int main() { Object value; boost::statechart::fifo_scheduler<> scheduler; const boost::statechart::fifo_scheduler<>::processor_handle processor1 = scheduler.create_processor <Test, Object&> (boost::ref(value)); return (0); } ---- Here's the compiler error: ---- g++ -Wall -lboost_system-mt -lboost_thread-mt -o test test.cc /usr/include/boost/noncopyable.hpp: In copy constructor 'Object::Object(const Object&)': test.cc:9: instantiated from 'typename boost::statechart::processor_container<boost::statechart::fifo_scheduler <FifoWorker, Allocator>, typename FifoWorker::work_item, Allocator>::processor_handle boost::statechart::fifo_scheduler<FifoWorker, Allocator>::create_processor(Arg1) [with Processor = Test, Arg1 = Object&, FifoWorker = boost::statechart::fifo_worker<std::allocator<void> >, Allocator = std::allocator<void>]' test.cc:36: instantiated from here /usr/include/boost/noncopyable.hpp:27: error: 'boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)' is private test.cc:9: error: within this context /usr/include/boost/statechart/fifo_scheduler.hpp: In member function 'typename boost::statechart::processor_container<boost::statechart::fifo_scheduler <FifoWorker, Allocator>, typename FifoWorker::work_item, Allocator>::processor_handle boost::statechart::fifo_scheduler<FifoWorker, Allocator>::create_processor(Arg1) [with Processor = Test, Arg1 = Object&, FifoWorker = boost::statechart::fifo_worker<std::allocator<void> >, Allocator = std::allocator<void>]': /usr/include/boost/statechart/fifo_scheduler.hpp:63: note: synthesized method 'Object::Object(const Object&)' first required here /usr/include/boost/statechart/fifo_scheduler.hpp:63: error: initializing argument 3 of 'WorkItem boost::statechart::processor_container<Scheduler, WorkItem, Allocator>::create_processor(boost::weak_ptr<std::auto_ptr<boost::statec hart::event_processor<Scheduler> > >&, Scheduler&, Arg1) [with Processor = Test, Arg1 = Object, Scheduler = boost::statechart::fifo_scheduler<boost::statechart::fifo_worker<std::al locator<void> >, std::allocator<void> >, WorkItem = boost::function0<void>, Allocator = std::allocator<void>]'

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[Review Results] Range.Ex library accepted into boost
by Thorsten Ottosen 27 Apr '09

27 Apr '09

Dear all, It is my pleasure that Neil Groves' RangeEx library has been accepted into boost. Congratulations Neil! There are quite a number of minor issues that need to be resolved before the library is release ready, see below for a summary. Review statistics ----------------- Full Reviews: 8. Discussion: extensive. I had the clear impression that everybody that participated in the discussion were in favor of this library, albeit they did not have time to submit a full review. I did not hear a single statement saying that this library should be rejected. Thanks to everybody that participated in the review and its discussions. Issue Summary ------------- Below is given a list of topics that must be adressed before the library can be included into boost. In general, we should try to discuss them one at a time in seperate threads. Many people suggested various extensions, new algorithms (e.g. from adope), etc. **In general we should not require Neil to add all these if he does not have the time currently: the basic infrastructure, the concepts, the naming and organization of the library is much more important. Then we can add all these things later.** 1: documentaion =============== The documentation should clearly reflect if an algorithm delegates to a standard algorithm. If the algorithm is new, then it should state complety and exception-safety. More examples would be welcome. Sometimes the rationale and explanations could be improved, e.g for operator|(). 2: return type specification for find() etc =========================================== There where no major objection to the mechanism, but some found the syntax ugly. I believe the suggested syntax (e.g.) boost::find[_f,_e]( range, x ) boost::find[_f+1,_e]( range, x ) was considered good by most. 3: namespace organization ========================= Currently the library uses the namspaces boost boost::adaptors Some raised concern about putting the algorithms straight in the boost namespace before we have a general agreement on where to put algorithms (e.g. in boost::algorithm or boost::ranges or whatever). I think it will make sense to put each algorithm in its own header, since we might have to include additional standard library headers for calling algorithms that are implemented as member functions (but see 7 below). Feedback is most welcome. 4: naming convention for adaptors ================================= The following have been proposed throughout the review (here examplified with "transform"): | transformed( fun ) | transform( fun ) | transform_view( fun ) | view::transform( fun ) There where no consensus during the review. Other libraries seem to use the _view suffix, which is a strong argument for that candidate (in that case, I suggest to drop the adaptors namespace). 5: naming convention for the adaptor generators =============================================== Many people like to be able to say make_transform_range(r,fun) instead of r | transformed( fun ). There was no concensus on how to name these functions. Here are some candidates: make_transform_range( r, fun ) transformed( r, fun ) transform( r, fun ) (*) transform_view( r, fun ) (*) was dislike by some because it has exactly the same spelling as the algorithm transform. Many felt that the confusion is too big if view generators are not named different from the actual algorithms. 6: reintroducing _if variants of algorithms =========================================== An important problem with the suggested approach was the the iterator returned by an algorithm after applying | filtered( pref ) are now filtered iterators and so one needs to manually unwrap the return iterator. This provided enough justification for reintroducing these algorithms. (One could imagine that this unwrapping was done automatically by a conversion operator such that iterator i = boost::find( r | boost::filtered( pred ), x ); "just worked". However, the syntax is still slightly worse than just using the original algorithm). Generic programming is concerned with the use of orthogonal concepts which put together yields all possible combinations of algorithms. If we reintroduce all _if algorithms, we have to aks ourselves "when does it end?". Should all new algorithms then simply add _if variants? This seems very much against the spirit of generic programming. The problem with the iterators being changed (as in the find example) seems to suggest the following guideline: "If the algorithm returns an iterator, it makes sense to provide an _if overload. Otherwise it does not." Under this guideline, find_if() should be there, but count_if() should not be provided. 7: should algorithms call member function when possible? ======================================================== I heard one strong voice against this. The reason was that the algorithm implemented as member function often has quite different guarantees w.r.t. complexity, reference and iterator stabililty. I think this is a very strong argument. Also, we can add this later if good arguments appear, but it is much harder to take away. We also have to remember Scott Meyers item "Beware of container independent code" which also suggest that this is a bad idea. At the very menimum, the original algorithm and the member function should have similar semantics. This seems to suggest that we can call set::lower_bound() from boost::lower_bound(). In that case, the best way would probably be to add these as overloads in the boost namespace: template< class T, class A > typename std::set<T,A>::iterator lower_bound( std::set<T,A>& s ); template< class T, class A > typename std::set<T,A>::const_iterator lower_bound( const std::set<T,A>& s ); 8: making return values of algorithms consistent/intuitive ========================================================== For example, sort(r) returns the sorted range, but sort_heap(r) does not. Similar issues for partial_sort(). Please go through all algorithms to see if this done correctly. 9: output range concept? ========================= It appears that the only use for an output iterator in the library was for boost::copy(rng,iter), and the only use for that function was for "sinks" like std::ostream_iterator<T>(...). This seems to be the only safety hole left in the library. Here's an idea to how we might remove that: create a new "copy sink" concept: struct array_copy_sink { ... template< class Iterator > copy( Iterator begin, Iterator end ) { ... } }; Then we might imagine boost::copy( rng, boost::ostream_sink(std::cout) ); boost::copy( rng, boost::array_sink(an_array) ); boost::copy( rng, boost::ptr_sink(begin,end) ); boost::copy( rng, boost::front_insert_sink(a_deque) ); ... For optimal performance, we also need a "nonoverlapping copy sink" concept, and an algorithm that expects that sink (or that boost::copy() determines the type of the sink automatically). 10: automatic projection ======================= Adope has algorithms overloaded such that projection is very easy: struct my_type { int member; double another_member; }; //... my_type a[] = { { 1, 2.5 }, ... }; // sort the array by the first member: sort(a, less(), &my_type::member); my_type* i = lower_bound(a, 5, less(), &my_type::member); We should be able to express this well, albeit not as concise, with my_type* i = boost::lower_bound( a | project( &my_type::member ), 5, less() ); where project( ... ) could simply return a transform iterator constructed with boost::bind(). There is another problem, however, because now the return value is a tranform_iterator of some form. Appending .base() would solve it, albeit it is somewhat ugly. Again this might raise the question of an implicit conversion. I just want to say this is not a critical issue as we can always add these overloads. --- End of Issues ---- Again, I would like to thank everybody that participated in the review. best regards Thorsten, review manager

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[preprocessor] Nested FOR_EACHs
by Reimund Klemm 27 Apr '09

27 Apr '09

Hello, is it possible to nest FOR_EACH statements with the preprocessor? In my example it seems not to work: #include <boost/preprocessor/seq/for_each_i.hpp> #define DECLARE_TEST2(r,data,i,elem) \ 1; /**/ #define DECLARE_TEST(r,data,i,elem) \ BOOST_PP_SEQ_FOR_EACH_I(DECLARE_TEST2,data,data); /**/ #define SEQ ((1)(NACK_SN)(10)) ((1)(E1)(1)) ((1)(E2)(1)) int main(){ BOOST_PP_SEQ_FOR_EACH_I(DECLARE_TEST,SEQ,SEQ) return 0; } Thanks a lot for comments. Reimund

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[Spirit] leaf_node_d compile time error
by Chris Uzdavinis 26 Apr '09

26 Apr '09

Hi, I'm upgrading some code from boost 1.33 to 1.38, and upgrading compilers from gcc 4.1 to 4.3.3. Code that used to work is no longer compiling, and I'm running out of ideas what might be the problem. While the real code is significantly larger, I've managed to extract the problem down to this short example. #define BOOST_SPIRIT_USE_OLD_NAMESPACE #include "boost/spirit/include/classic_core.hpp" #include "boost/spirit/include/classic_ast.hpp" using namespace boost::spirit; struct Test_Parser : public grammar<Test_Parser> { template <typename ScannerT> struct definition { definition(Test_Parser const & /*self*/) { test_filter = leaf_node_d[ ch_p('=') ] //<<<<<<< HERE ; } rule<ScannerT> test_filter; rule<ScannerT> const & start() const { return test_filter; } }; }; int main() { using namespace boost::spirit; char const * str = "="; Test_Parser parser; parse_info<> info = parse(str, parser, space_p); } When I use leaf_node_d[], it doesn't compile. Removing leaf_node_d, and all is well. The error is ugly, but ultimately is this: error: no type named node_factory_t in class boost::spirit::leaf_node_parser<T>::parse(const ScannerT&) const I've spent a few hours trying to grok the code and am falling short. Any help would be appreciated. g++ -I $BOOST_ROOT foo.cpp /usr/local43/include/boost-1_38/boost/spirit/home/classic/tree/common.hpp: In member function typename boost::spirit::parser_result<boost::spirit::leaf_node_parser<T>, ScannerT>::type boost::spirit::leaf_node_parser<T>::parse(const ScannerT&) const [with ScannerT = boost::spirit::scanner<const char*, boost::spirit::scanner_policies<boost::spirit::skipper_iteration_policy<boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, T = boost::spirit::chlit<char>]: /usr/local43/include/boost-1_38/boost/spirit/home/classic/core/non_terminal/impl/rule.ipp:235: instantiated from typename boost::spirit::match_result<ScannerT, ContextResultT>::type boost::spirit::impl::concrete_parser<ParserT, ScannerT, AttrT>::do_parse_virtual(const ScannerT&) const [with ParserT = boost::spirit::leaf_node_parser<boost::spirit::chlit<char> >, ScannerT = boost::spirit::scanner<const char*, boost::spirit::scanner_policies<boost::spirit::skipper_iteration_policy<boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, AttrT = boost::spirit::nil_t] foo.cpp:28: instantiated from here /usr/local43/include/boost-1_38/boost/spirit/home/classic/tree/common.hpp:903: error: no type named node_factory_t in class boost::spirit::leaf_node_parser<T>::parse(const ScannerT&) const [with ScannerT = boost::spirit::scanner<const char*, boost::spirit::scanner_policies<boost::spirit::skipper_iteration_policy<boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, T = boost::spirit::chlit<char>]::result_t make: *** [.obj/foo.o] Error 1 -- Chris

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Boost Graph Library documentation unclear
by Lindley M French 26 Apr '09

26 Apr '09

I've been trying to use the Boost Graph Library. For the most part I'm working it out. However, I'm finding the documentation annoyingly decentralized....it isn't interlinked enough, at the very least. Too hard to go from "how do I use X" to "oh, here's the documentation on X." Took me half an hour just to find *something* on the add_edge function (turns out it's on the Concepts page?), and what's there *barely* qualifies as a prototype, much less a proper man page. My current question is regarding properties. Some of the algorithms specify the "edge_weight" property as if it's something all edges have, and the vertex_index property as if it's something all vecS-specified graphs have. Yet I can't find any documentation explicitly confirming this, and my compiler seems to disagree in any case. http://www.boost.org/doc/libs/1_38_0/libs/graph/doc/kruskal_min_spanning_tr… Can something be done about the state of the documentation, and is there a comprehensive list of default properties available somewhere (together with how those are replaced or supplemented when user properties are introduced)?

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initializing intrusive_ptrs through library calls
by Zachary Turner 26 Apr '09

26 Apr '09

I frequently use COM, and I've written an add_ref() and release() so that I can use my COM objects with boost::intrusive_ptr. However, one generally obtains these pointers through a library call that accepts a T** or a void**, and returns a pointer that's already been AddRef'd the first time. Normally it would go something like this: template<typename T> d3d_ptr<T> take_ptr(T* t) { return d3d_ptr<T>(t, false); } ID3DXFont* pFont = NULL; D3DXCreateFontIndirect(m_pDeviceObject, &fontDesc, &pFont); m_spFont = take_ptr(pFont); To remove these extra 2 lines I wrote the following class / function: template<typename T> class recv_by_addr_t { public: recv_by_addr_t(d3d_ptr<T>& r) : m_auto(r), m_raw(NULL) {} ~recv_by_addr_t() {m_auto = take_ptr(m_raw);} operator T**() { return &m_raw; } private: T* m_raw; d3d_ptr<T>& m_auto; }; template<typename T> recv_by_addr_t<T> recv_by_addr(d3d_ptr<T>& rptr) { return recv_by_addr_t<T>(rptr); } And I can now call the function like this: D3DXCreateFontIndirect(m_pDeviceObject, &fontDesc, recv_by_addr(m_spFont)); I feel like this is pretty solid, but figured I should ask the gurus :) Even in the case where the function errors out and sets the thing to NULL, the original pointer should still get correctly released. Anything wrong with this approach?

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Boost 1.39.0 beta 1 is available for download
by Beman Dawes 26 Apr '09

26 Apr '09

Boost 1.39.0 beta 1 is available for download from SourceForge. See http://sourceforge.net/project/showfiles.php?group_id=7586&package_id=8041&… New Libraries: Signals2. Updated Libraries: Asio, Flyweight, Foreach, Hash, Interprocess, Intrusive, Program.Options, Proto, PtrContainer, Range, Unordered, Xpressive. Updated Tools: Boostbook, Quickbook. Plus the usual bug fixes to numerous libraries. Please report any problems to the Boost users or developers mailing list. Thanks, --Beman Dawes, Daniel James, and all the other Boosters who help get releases out

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