October 2010 - Boost-users - lists.preview.boost.org

this_thread::sleep hangs on local clock change
by Goldshmidt, Mark 25 Oct '10

25 Oct '10

Hello, We're using boost::thread library in a consumer application. Part of the requirements for the application is to continue operation when the user changes local time. Our problem is that if local time is set backwards X minutes during a call to this_thread::sleep(duration) the thread sleeps for X minutes+duration. This happens on MacOS in release build, but not in debug. On Windows behavior is correct. I didn't have a chance to check other platforms. I believe that the intention of this_thread::sleep(duration) is to suspend thread execution for <duration> period regardless of local clock setting, and provide consistent behavior across all platforms and build configurations. Looking into the code of libs/thread/src/pthread/thread.cpp I see that problematic flow may occur in case of detail::get_current_thread_data() is returning null. Apparently this is what causes different behavior in debug and release. The "offendinng" code tries to make sure that absolute point in time (current time + requested delay) is reached using 5 attempts and calculating necessary sleep duration each time. So if during the first sleep local clock is set backwards, second sleep will try to "compensate" for the new difference. The simplest workaround for the problem I could think of is to replace the first statement of the sleep(...) function: detail::thread_data_base* const thread_info= detail::get_current_thread_data(); with this one: detail::thread_data_base* const thread_info= get_or_make_current_thread_data(); Would it create any unwanted side effects? Is there a better way to deal with is problem? Thanks in advance, Mark This message is confidential and intended only for the addressee. If you have received this message in error, please immediately notify the postmaster(a)nds.com and delete it from your system as well as any copies. The content of e-mails as well as traffic data may be monitored by NDS for employment and security purposes. To protect the environment please do not print this e-mail unless necessary. An NDS Group Limited company. www.nds.com

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extents
by Alle Meije Wink 25 Oct '10

25 Oct '10

Dear all, I am trying to load data from a file, where they are (obviously) stored as a 1D contiguous block, to a N-dimensional array. For the type of files I use N could be 1 through 8. I have code to for a 1..8-dimensional container (as a class template), but how to load in the data from the file? The multi_array_ref way to do it looked ideal, eg for a 3D float-image something like im = image_ref< float, 2 >( image->data, boost::extents[512][512] ) might work. But to code the different dimensionalities in a neat way would mean to store the extents in a variable (or something), like boost_extents_type e; switch ndim { // ndim=dim[0] 1: int dim1=dim[1]; e=boost::extents[dim1]; break; 2: int dim1=dim[1],dim2=dim[2]; e=boost::extents[dim1][dim2]; //etc } Is something like this possible with extents? Many thanks, Alle Meije

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[program_options] How to use "notifier" in options_description with member functions?
by Carlos Franke 25 Oct '10

25 Oct '10

Hello! I am looking for advice about the use of the "notifier" function in program_options::options_description with class methods. My problem seems very basic to mee, yet I wasn't able to find the (any) related documentation. Here is a minimal example of what I cannot get to work: struct test { void function(int i) {std::cout << i << std::endl;} void does_not_compile() { po::options_description desc; desc.add_options() ("option", po::value<int>()->notifier(&test::function), "Option") ; } }; Compilation fails with: […] test.cpp:62:82: instantiated from here /usr/include/boost/function/function_template.hpp:225:11: error: no match for call to '(boost::_mfi::mf1<void, test, int>) (const int&)' /usr/include/boost/bind/mem_fn_template.hpp:163:7: note: candidates are: R boost::_mfi::mf1<R, T, A1>::operator()(T*, A1) const [with R = void, T = test, A1 = int] /usr/include/boost/bind/mem_fn_template.hpp:184:7: note: R boost::_mfi::mf1<R, T, A1>::operator()(T&, A1) const [with R = void, T = test, A1 = int] Sorry if this is trivial. Your help is all the more appreciated! Carlos

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[asio] udp sendto performance bottleneck
by Hajo Kirchhoff 25 Oct '10

25 Oct '10

Hi all, I am porting an application from linux (suse 11) to windows. This application is sending 75.000 UDP Pakets per second, 1416 bytes each. It uses sendto. IOW: the application is calling sendto approx 75.000 times per second. The GBit LAN utilization is in the 80-90% range. This works fine under linux, but the sendto call under windows takes way longer than under linux. The overhead is so high that throughput drops from about 100MB/s to less than 20MB/s. This seems to be a known problem with the windows sendto call, as cygwin has a rather complex sendto implementation/emulation and does not suffer from this problem. They are using WSASendMsg internally and pass multiple buffers with one system call. WSASendMsg passes an array of buffers to the networking stack and my impression is that it allows sending several packets with one system call. My question: Is it possible to send multiple udp pakets with one asio::sendto call? asio::sendto accepts multiple buffers but seems to combine all them into one udp paket. Is there a way to prevent that? Specifically I want to do the following: vector<array<char, 1416> > b; b.push_back(paket1); b.push_back(paket2); b.push_back(paket3); ... m_socket.sendto(b); This should send three udp pakets with 1416 bytes each instead of one udp paket with 3*1416 bytes. How can I do that? Is this possible? Regards Hajo (Sidenote to all people with dropped udp pakets under windows Vista and 7: Have you set the network throttling index to 0xffffffff? Its a registry key and without it you'll never reach maximum throughput. Another important aspect is to set the receive buffer count in your network driver to maximum - usually 512 or more - and to use a good network card. It _is_ possible to receive close to one Gigabit/sec UDP pakets if done right. Thanks to asio it is also rather easy :-)

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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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