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[1.44 MSM meta state machine] accessing objects from actions
by Hajo Kirchhoff 25 Oct '10

25 Oct '10

Hi all, what is the recommended way to use objects with an MSM state machine? I've written a state machine that handles sending data via UDP (asio). I'm using the functor front end and I have a 'send' action: struct a_send { template <typename Event, typename Fsm, typename S, typename T> void operator()(Event const& evt, Fsm &fsm, S&, T&) { // get next object from queue and post it to asio } }; My question is, how are actions supposed to access the objects that the state machine should work with? Currently my queue object is a member of the state machine itself, so I can write struct Send_ : public msm::front::state_machine_def<Send_> { string m_next_line_to_send; socket m_socket; string get_next_send_line(); }; and in my a_send action void operator()(Event &const &evt, Fsm &fsm, S&, T&) { fsm.m_next_line_to_send=fsm.get_next_send_line(); fsm.m_socket.async_write(fsm.m_next_line_to_send); } This works well as long as I am not using sub-statemachines. Here is my problem: I would like to use a substate machine for the actual sending. The main state machine has the states Disconnected, Working, Error, Shutdown. The Working state should actually be a substate machine. The problem is, when a_send gets called by the substate machine Working, the fsm object is of type Working. How can I access the member variables of the parent of a substate machine? Or is there a better way of accessing the objects the state machine should work with from actions? The tutorial explains state machines very nicely with the example of a CD player. But all the actions are empty and nowhere is explained, how you would actually access a CD player member variable or other such object so that you could actually manipulate the player to do something. Regards and thanks Hajo

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[OT] Can I count on order of template matching of array dimensions
by Patrick Horgan 24 Oct '10

24 Oct '10

Off topic. Feel free to ignore. About baby template meta-programming. Working my way through "C++ Template Metaprogramming" by Abrahams and Gurtovoy, and am doing exercise 2-3/4. This: template<typename T,size_t D> struct type_descriptor<T[D]> { static std::ostream& print(std::ostream& os) { os << type_descriptor<T>() << '[' << D << ']'; return os; } }; When asked to deal with a type, for example, char[7][8][9] results in the reversal of the indices and prints char[9][8][7]. I can deal with that, (see the p.s. at the end), but it made me curious. That implies that the compiler is seeing it like ((char[9])[8])[7] which makes sense. It's an array of length 7 of arrays of length 8 of arrays of length 9 characters. That's C/C++ row-major order. It has 7 tables each of which has 8 rows of 9 characters. My question is this. Can I count on this? I don't mean row-major order, I mean that the compiler will always match in this order. Is this matching BECAUSE of row-major order, or is it compiler dependent? Wait, never mind. I just thought it through. The implication, if it had done it textually as I expected, is that T would have had type char[7][8], and the second time, T would have had type char[7] which would have been a completely different beast. Well. I'm not really asking the question now after all, just throwing this out in case it helps anyone else's understanding. Please feel free to ignore. lol! I'm also implementing all of the is_char, is_array, remove_reference etc. metafunctions instead of using the boost or c++0x ones. I figure that way by the time I get through the book I'll have more understanding. That has given me questions, because after I implement each one, I look at the boost implementation, and I look at the the gcc libstdc++ implementation of the c++0x ones and generally they are, in order of reducing complexity, boost, gcc, me. Some of the difference in complexity is that boost needs to work with different compilers on different architectures, and gcc has to work with different architectures, and I just have to get it to compile on my machine (ubuntu maverick meercat on a dell inspiron 1420 laptop) with the gcc compiler (last night's pull from trunk) that I'm using. Other times, though, it LOOKS to me like there's extra complexity for nothing (I think brought about by the desire for maximal code reuse, i.e. don't include something in your template when you can invoke another cool metafunction to do it for you, but at the expense of higher compile-time complexity). I'll hold off on questions like that, though, until I finish the book in case the answers are in there. ;p Patrick p.s. if anyone cares, here's what I came up with (with the char base type type_descriptor so you can do std::cout << type_descriptor[7][8][9]). Any comments, improvements, critiques, and alternate implementations welcome: template<typename T> struct print_dimensions { // handles exit condition for recursive print_dimensions static std::ostream& print(std::ostream&os) { return os; } }; template<typename T,size_t D> struct print_dimensions<T[D]> { static std::ostream& print(std::ostream&os) { // print our dimension and invoke ourselve recursively to do the next os << '[' << D << ']'; print_dimensions<T>::print(os); return os; } }; template<typename T> struct remove_all_dimensions { // when no more dimensions this is the stop condition for the recursion typedef T type; }; template<typename T, size_t D> struct remove_all_dimensions<T [ D ]> { // recurse to ask our type with one less dimension to define the type for us typedef typename remove_all_dimensions<T>::type type; }; template<typename T> struct type_descriptor<char> { static std::ostream& print(std::ostream& os) { os << " char"; return os; } }; template<typename T,size_t D> struct type_descriptor<T[D]> { static std::ostream& print(std::ostream& os) { // pull off all the dimensions, print the base type, then ask print_dimensions to print the dims. os << type_descriptor<typename remove_all_dimensions<T>::type>(); print_dimensions<T[D]>::print(os); return os; } }; p.p.s This is really fun! p.p.p.s Does anyone know of a mailing list to discuss beginning TMP? Patrick again ;p

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asio nntp reading data
by Kraus Philipp 24 Oct '10

24 Oct '10

Hello, I try to read the newsgroup list with aiso, but I've got some problems with terminate the reading. I send the "list" command to my nntp server and get a status 200, after that I read the data with boost::asio::streambuf l_response; std::istream l_response_stream( &l_response ); boost::system::error_code error; while (boost::asio::read(m_socket, l_response, boost::asio::transfer_at_least(1), error)) std::cout << &l_response; and I see on cout the list (excerpt): xs4all.ipv6 0000000481 0000000001 y de.comp.lang.vbclassic 0000000257 0000000001 y de.comp.office-pakete.ms-office.word 0000000013 0000000001 y it.comp.dotnet 0000000074 0000000001 y free.timothy.sutter 0000000003 0000000001 y free.soc.religion.christian 0000000006 0000000001 y free.fan.taylor-momsen 0000000000 0000000001 y . After the dot, my program doesn't terminate, because the while loop doesn't break. I understand the loop in that way: I read some bytes into my stream from the socket and write them to the std::cout, if there more bytes the loop will continue otherwise (like EOF) the look should be break. I use the example at http://www.boost.org/doc/libs/1_44_0/doc/html/boost_asio/example/http/clien… because I'm new on asio, so I hope someone can explain me, the problem. Thanks for help Phil .

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Finite State Filters
by Kraus Philipp 24 Oct '10

24 Oct '10

Hi, I've found http://www.boost.org/doc/libs/1_44_0/libs/iostreams/doc/tutorial/finite_sta… for filtering stream data. I've got a stream which I would filter with a state filter, because I must check some data and substitute them. Now I try to create a state struct, but I can't compile it, because the headers on the page seems to be not correct. I use a a istream, in which the data saved, now I would send them through the state machine filter for get my output data. My first try was to create the states with a boost::mpl::vector, but the example on the page doesn't work because the compiler can't find the "row" deklaration. Is there an example for a full state filter, that works? Or should I use the boost spirit? I would like to filter my stream data. Thanks for help Phil

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[thread] unlock
by gast128 23 Oct '10

23 Oct '10

Hello all, When using unique_lock in combination with mutex, one should only lock / unlock thru the unique_lock, otherwise its managment gets corrupted. However the unlock fct. is also offered in the mutex, which makes it vunerable for small typo errors like (code simplified): void foo() { boost::mutex mtx; for (size_t n = 0; n != 2; ++n) { boost::unique_lock<boost::mutex> lck(mtx); //mtx.unlock(); //hang in next lock attempt lck.unlock(); //ok } } Not sure if something can be done about this; mail only meant to share information.

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[date-time] Getting time from midnight in nanoseconds
by ppatel＠efs-us.com 22 Oct '10

22 Oct '10

I am resending this with proper subject line. Thanks From: Priyank Patel Sent: Friday, October 22, 2010 8:47 AM To: boost-users(a)lists.boost.org Subject: Getting time from midnight in nanoseconds Hi, Can you please tell me if there is a way to get current time in nanoseconds using boost date_time library? I have tried following but it doesn't seems to be returning values in nanoseconds. I know I have used microsec_clock and that might be the problem but not sure what alternate to use. Any help will be appreciated. hrtime_t getCurrentTime() { boost::posix_time::ptime recvTime = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration duration( recvTime.time_of_day() ); return duration.total_nanoseconds(); // This call returns values in microseconds (last three digits are always zero in returned value) } Thanks Priyank

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Re: [Boost-users] [Pool] Problems using Boost.Pool with the Eigen matrix library
by lfrfly＠icqmail.com 22 Oct '10

22 Oct '10

>2010/10/14 <lfrfly(a)icqmail.com>: >> Since Eigen matrices and vectors use SSE and therefore require a particular >> alignment, Eigen requires that when these types (specifically, the >> compile-time sized versions) are within a struct or class, that struct be >> given the EIGEN_MAKE_ALIGNED_OPERATOR_NEW macro. > >What we do require is that e.g. Vector4f's be created at 16 byte >aligned locations. EIGEN_MAKE_ALIGNED_OPERATOR_NEW is just one way of >doing that. > >> >> But here's the problem. What if that struct is allocated by a >> boost::pool_allocator<T>? Is there any way to enforce alignment then? > >That's a question for boost::pool_allocator, not for us; if this >allocator doesn't give you 16 byte alignment, then you need a >different allocator (or just modify this allocator to meet this >criterion). > >The allocator is what gives you an address. If it's giving >non-16-byte-aligned addresses, then it can't be used. > >Benoit It's now clear that this question belongs firmly on the Boost.Pool side of the fence, so here it is---I'm wondering why boost::pool_allocator isn't designed to work with a standard-compliant allocator as its second template parameter? I tried creating a boost::fast_pool_allocator<T, Eigen::aligned_allocator<T>>, but this failed with a compile error----apparently fast_pool_allocator has an unusual notion of what concept a UserAllocator should satisfy, requiring the methods malloc() and free(). Why does it not accept any standard allocator, which will instead provide allocate() and deallocate()? This seems like a serious shortcoming.

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building boost with the windows sdk 7.1
by Sean Farrow 22 Oct '10

22 Oct '10

Hi: I need to build boost with the windows sdk v7.`1. I've got vs2010 (10.0) instaloled and the sdk. If there anything specific I need to do to build with 7.1 as aposed to 7.0? Cheers Sean.

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Re: [Boost-users] [boost] What's so cool about Boost.MPI?
by Brian Wood 22 Oct '10

22 Oct '10

>At Thu, 21 Oct 2010 14:25:38 -0500, >Brian Wood wrote: >> >> David Abrahams: >> > Which yields huge performance benefits and makes practical some >> > computations that might otherwise not be, due to resource constraints >> >> I've been exploring this further here - >> http://www.gamedev.net/community/forums/topic.asp?topic_id=585405 >> >> Also, from what I can tell, MPI messages are composed of one >> data type or an array of one type. > > Maybe, but the library lets you easily make arbitrarily complex data > types (described to MPI as MPI type maps). Right, I don't deny that. > >> If that's the case, I'd argue there's room for more coolness. > >What more do you want? Here's an example from my work. I have a three-tier architecture: C++ Middleware Writer (server) | C++ Middleware Writer Ambassador (server) | command line program that exits I'll introduce a struct that I don't currently use, but that might make this easier to follow. struct RequestData { uint32_t accountNumber; uint32_t transactionNumber; std::vector<File> includeFiles; std::auto_ptr<File> middleFile; uint32_t userOptions; }; I could use that to send a message, but being forced to receive those fields as a unit would be detrimental to the implementation of the C++ Middelware Writer. The account number is used to determine how the files are received. A directory is associated with each account. If I couldn't break the account number out of there, I'd have to receive the files into a temporary directory and then move them into the right directory later and get rid of the temporary directory. So I do it something like this: struct TransactionData { uint32_t transactionNumber; std::vector<File> includeFiles; std::auto_ptr<File> middleFile; uint32_t userOptions; }; That's the same as RequestData, but the account number field has been removed. This middle code describes how the message is sent (@out) and received (@in): (uint32_t, TransactionData) @out @msg_id_direct (uint32_t) @in (TransactionData) @in The sending process sends 2 items as one message. The receiving process receives the message in two steps. First it gets the account number as a uint32_t which it uses to receive the balance of the message. I believe accomplishing the same thing with MPI would involve two message ids (tags) and would require more work to be certain that the messages are sent and received in the correct order. There's needless overhead associated with the additional message id and the programming is more involved to make sure everything is kosher. -- Brian Wood Ebenezer Enterprises http://webEbenezer.net (651) 251-9384

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Printer Friendly Proto
by Hossein Haeri 22 Oct '10

22 Oct '10

Dear all, How can I get a printer friendly version of the complete Proto documentation? http://boost.org/doc/libs/1_44_0/doc/html/proto.html A PDF version say? (I'm going to read it in bus, bus-stop, etc etc. So, the webpage is not very useful without internet connection. Furthermore, I take it that Chapter 15 of the Boost book is now completely outdated...) TIA, --Hossein

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