April 2021 - Boost-users - lists.preview.boost.org

Clarification on statechart post_event vs process_event within react()
by John McCabe 10 Jan '22

10 Jan '22

Hi, Apologies if this has already been answered/clarified, but my search of the internet to try to get a definitive answer, at least one I recognised as being definitive, was unsuccessful. Below I have posted some source code, based on the stopwatch example from the tutorial, but using an 'external' object to delegate the actual handling of event stuff to and using the state, rather than simple_state base class, and some other tweaks. This is a cut down version of something that someone I work with has devised, but I just wanted to get a clear answer on whether process_event() should be getting called in cases like this. I think it probably should not since, in the code below, you change state (with a state object's destructor being executed) whilst you're executing that state's react(EvStartStop) function. If someone can confirm this is the correct interpretation that would be very much appreciated. Any questions, feel free to ask (BTW - I'm compiling for C++17) John PS - In case it's of any use, the output from running this code is: ------ Entered Active Entered Stopped Stopped - payload2 m_charValue: a Exited ~Stopped <<<--- This is the bit I don't like the look of because... Entered Running Active - payload2 m_charValue: a <<<--- ... this happens from the forward_event() call payload1 value1: 20 payload1 value2: 200.2 Exited ~Running Entered Stopped Exiting Program Exited ~Stopped Exited ~Active ------ If I swap the //*** comments to the doProcess() lines instead of doPost(), the output seems more sensible ------ Entered Active Entered Stopped Stopped - payload2 m_charValue: a Exited ~Stopped Entered Running Active - payload2 m_charValue: a payload1 value1: 20 payload1 value2: 200.2 Exited ~Running Entered Stopped Exiting Program Exited ~Stopped Exited ~Active ------ ========== code =========== #include <boost/statechart/event.hpp> #include <boost/statechart/state_machine.hpp> #include <boost/statechart/state.hpp> #include <boost/statechart/transition.hpp> #include <boost/statechart/custom_reaction.hpp> #include <boost/mpl/list.hpp> #include <iostream> #include <string> namespace sc = boost::statechart; namespace mpl = boost::mpl; // Forward declare a handler 'class' that's going to have activity delegated to it struct Handler; // Normal example start/stop and reset events struct EvStartStop : sc::event<EvStartStop> {}; struct EvReset : sc::event<EvReset> {}; // A couple of events that carry data with them struct EvPayload1 : sc::event<EvPayload1> { EvPayload1(int value1, double value2) : m_value1 { value1 }, m_value2 { value2 } {}; int m_value1 { 0 }; double m_value2 { 0.0 }; }; struct EvPayload2 : sc::event<EvPayload2> { EvPayload2(const char& charValue) : m_charValue { charValue } {}; char m_charValue { false }; }; // Back to the example bits struct Active; struct StopWatch : sc::state_machine<StopWatch, Active> { typedef sc::transition<EvReset, Active> reactions; // The extra 'handler' stuff void setHandler(Handler* handler) { m_handler = handler; }; Handler* getHandler() const { return m_handler; }; Handler* m_handler { nullptr }; // Used to make post_event() accessible from an external class...seems unpleasant, but... using sc::state_machine<StopWatch, Active>::post_event; }; // The implementation of the Handler class; created with a reference to a StopWatch object struct Handler { Handler(StopWatch& stopWatch) : m_stopWatch { stopWatch } {}; void doPost() { m_stopWatch.post_event(EvStartStop()); } void doProcess() { m_stopWatch.process_event(EvStartStop()); } StopWatch& m_stopWatch; }; struct Stopped; struct Active : sc::state<Active, StopWatch, Stopped> { Active(my_context ctx) : my_base { ctx } { std::cout << "Entered Active" << std::endl; }; ~Active() { std::cout << "Exited ~Active" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload1>, sc::custom_reaction<EvPayload2>, sc::transition<EvReset, Active>> reactions; sc::result react(const EvPayload1& payload1) { std::cout << "payload1 Event NOT HANDLED" << std::endl; return discard_event(); } sc::result react(const EvPayload2& payload2) { std::cout << "Active - payload2 m_charValue: " << payload2.m_charValue << std::endl; return discard_event(); } }; struct Running : sc::state<Running, Active> { Running(my_context ctx) : my_base { ctx } { std::cout << "Entered Running" << std::endl; }; ~Running() { std::cout << "Exited ~Running" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload1>, sc::transition<EvStartStop, Stopped>> reactions; sc::result react(const EvPayload1& payload1) { std::cout << "payload1 value1: " << payload1.m_value1 << std::endl; std::cout << "payload1 value2: " << payload1.m_value2 << std::endl; //***context<StopWatch>().getHandler()->doPost(); context<StopWatch>().getHandler()->doProcess(); return discard_event(); } }; struct Stopped : sc::state<Stopped, Active> { Stopped(my_context ctx) : my_base { ctx } { std::cout << "Entered Stopped" << std::endl; }; ~Stopped() { std::cout << "Exited ~Stopped" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload2>, sc::transition<EvStartStop, Running>> reactions; sc::result react(const EvPayload2& payload2) { std::cout << "Stopped - payload2 m_charValue: " << payload2.m_charValue << std::endl; //***context<StopWatch>().getHandler()->doPost(); context<StopWatch>().getHandler()->doProcess(); return forward_event(); } }; int main() { StopWatch myWatch; Handler myHandler(myWatch); myWatch.setHandler(&myHandler); myWatch.initiate(); myWatch.process_event(EvPayload2 { 'a' }); myWatch.process_event(EvPayload1 { 20, 200.2 }); std::cout << "Exiting Program" << std::endl; return 0; }

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Final Notice: BinTray is shutting down 1-May (that's SATURDAY)
by Marshall Clow 29 Apr '21

29 Apr '21

Bintray is “sunsetting” on the 1st of May. At that time, you will be unable to download boost releases from there. Before that time, their service will be occasionally interrupted. The web site has been updated, all the download links now refer to https://boostorg.jfrog.io/artifactory/main/release/ <https://boostorg.jfrog.io/artifactory/main/release/> Example: Instead of downloading from: https://dl.bintray.com/boostorg/release/1.76.0/source/boost_1_76_0.tar.gz <https://dl.bintray.com/boostorg/release/1.76.0/source/boost_1_76_0.tar.gz> You should download from: https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76… <https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76…> This applies to all releases from 1.63.0 onward (The pre-1.63 releases are still hosted at SourceForge) — Marshall

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[beast] help with http::dynamic_body and http::buffer_body
by Klebsch, Mario 26 Apr '21

26 Apr '21

Hello, After using boost::asio for several years I thought, I might give beast a try. I need to write a http server processing a POST request with an upload of a big file. So I thought, I could start with libs/beast/example/http/server/async. I soon found the function handle_request() and that I have to add something like if (req.method() == http::verb::post && req.target()=="/xxx" ) to catch the http POST transaction. But since I have to process the upload of a large file, I thought that using a http::string_body might not be the best choice. I found several other body types in the documentation. I thought buffer_body ought to be fine, since the documentation says: ‘This allows for serialization of body data coming from external sources, and incremental parsing of message body content using a fixed size buffer.’. incremental processing of the input stream is what I need. But now, I have no clue, how to change the example to use a buffer_body. I changed http::request<http::string_body> req_ to http::request<http::buffer_body> req_. But now I must process the request message in chunks. How do I get my callback invoked for each chunk? Without additional changes, I get a read error: need buffer. But the documentation on buffer_body does not help me. Buffer_body does not seem to have any methods, that I can call. It does have a member type reader, that is documented as implementation-defined. So there is nothing I can do with this reader. ☹ There is a member type value_type, that does have data, size and more mebers, but I have no idea, how I could et hold of a variable of this type containing a part of my message body. The error message might indicate, that I need to provide a fixed size buffer to the buffer_body, but I have no idea, how to do this. I tried to add the following code to do_read(): req_.body().data = my_buffer; req_.body().size = sizeof(my_buffer); It compiles, so req_body() seems to be the way to get hold on a http::buffer_body::value_type, but simply initializing the two variables does not seem to be sufficient. I also tried to set req_.body().more to false or to true, but it didn’t change anything. I then thought, I might try a dynamic_body. This would store the entire upload in memory, but perhaps I get more familiar with the beat framework, when I try to use this body. And in deed, I managed to write some code, that shows all request headers and the request body on stdout. To get the body, I had to copy the buffer contents into a std::string: std::string body{ boost::asio::buffers_begin(req.body().data()), boost::asio::buffers_end(req.body().data()) }; Since large files have to be handled by my code, this additional copy of the data is to be avoided. So I tried to iterate the body using the iterators: const auto begin = boost::asio::buffers_begin(req.body().data()); const auto end = boost::asio::buffers_end(req.body().data()); for (auto it = begin; it != end; it++) putchar(*it); While it runs fine on the windows box, the loop crashes on linux in the 512th iteration in it++. Program received signal SIGSEGV, Segmentation fault. 0x0000555555592432 in boost::intrusive::list_node_traits<void*>::get_previous (n=@0x7fffffffc118: 0x1ff) at ../boost/boost/intrusive/detail/list_node.hpp:54 54 { return n->prev_; } (gdb) print n $1 = (const boost::intrusive::list_node_traits<void*>::node_ptr &) @0x7fffffffc118: 0x1ff (gdb) Here is the call stack: #0 0x0000555555592432 in boost::intrusive::list_node_traits<void*>::get_previous (n=@0x7fffffffc118: 0x1ff) at ../boost/boost/intrusive/detail/list_node.hpp:54 #1 boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::basic_multi_buffer<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, (boost::intrusive::link_mode_type)0, boost::intrusive::dft_tag, 1u>, true>::operator-- (this=0x7fffffffc118) at ../boost/boost/intrusive/detail/list_iterator.hpp:107 #2 std::__advance<boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::basic_multi_buffer<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, (boost::intrusive::link_mode_type)0, boost::intrusive::dft_tag, 1u>, true>, long> (__i=..., __n=0) at /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_iterator_base_funcs.h:169 #3 0x000055555558daf0 in std::advance<boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::basic_multi_buffer<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, (boost::intrusive::link_mode_type)0, boost::intrusive::dft_tag, 1u>, true>, long> (__i=..., __n=-1) at /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_iterator_base_funcs.h:206 #4 0x0000555555589254 in std::prev<boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::basic_multi_buffer<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, (boost::intrusive::link_mode_type)0, boost::intrusive::dft_tag, 1u>, true> > (__x=..., __n=1) at /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/bits/stl_iterator_base_funcs.h:230 #5 0x0000555555589608 in boost::beast::basic_multi_buffer<std::allocator<char> >::subrange<true>::const_iterator::operator* (this=0x7fffffffc4f8) at ../boost/boost/beast/core/impl/multi_buffer.hpp:384 #6 0x0000555555589b4b in boost::asio::buffers_iterator<boost::beast::basic_multi_buffer<std::allocator<char> >::subrange<true>, char>::increment (this=0x7fffffffc4d0) at ../boost/boost/asio/buffers_iterator.hpp:370 #7 0x0000555555584894 in boost::asio::buffers_iterator<boost::beast::basic_multi_buffer<std::allocator<char> >::subrange<true>, char>::operator++ (this=0x7fffffffc4d0) at ../boost/boost/asio/buffers_iterator.hpp:229 #8 0x000055555557e7c0 in boost::asio::buffers_iterator<boost::beast::basic_multi_buffer<std::allocator<char> >::subrange<true>, char>::operator++ (this=0x7fffffffc4d0) at ../boost/boost/asio/buffers_iterator.hpp:237 #9 0x0000555555579ba8 in handle_request<boost::beast::http::basic_dynamic_body<boost::beast::basic_multi_buffer<std::allocator<char> > >, std::allocator<char>, session::send_lambda&> (doc_root=..., req=..., send=...) at t.cpp:164 I hope anybody can give my a hint on how to use this beast. Right now it feels that it might be easier to write the http server using plain boost::asio. Klebsch Mario Funktion | R&D Tel: +49 (0) 531 38 701 718 Raum: Braunschweig, E20 Diese E-Mail und die an sie angehängten Dateien sind ausschließlich für Personen oder Institutionen bestimmt, deren Namen oben aufgeführt sind. Sie können Informationen enthalten, die durch das Berufsgeheimnis geschützt sind und deren Weitergabe strengstens untersagt ist. Jede elektronische Nachricht kann geändert werden. ACTIA lehnt jede Verantwortung für diese Nachricht ab. Der Inhalt dieser Nachricht stellt keine Verpflichtung seitens unseres Unternehmens dar. Wenn Sie kein Empfänger sind, weisen wir Sie darauf hin, dass das Lesen, Vervielfältigen oder Verteilen strengstens untersagt ist. Wir bitten Sie daher, uns umgehend über diesen Brief zu informieren und diese Nachricht sowie eventuell beigefügte Unterlagen aus Ihrem Postfach zu löschen. Danke. This e-mail and the files attached to it are intended exclusively for persons or institutions whose names are listed above. They may contain information that is protected by professional secrecy and the disclosure of which is strictly prohibited. Any electronic message can be modified. ACTIA declines all responsibility for this message. The content of this message does not represent a commitment on the part of our company. If you are not a recipient, we would like to point out that reading, copying or distribution is strictly prohibited. We therefore ask you to inform us immediately about this letter and to delete this message and any accompanying documents from your mailbox. Thank you.

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Boost + Emscripten: .bc files?
by Rainer Deyke 22 Apr '21

22 Apr '21

I managed to successfully compile a subset of Boost for Emscripten using the emscripten toolset. However, this for some reason produces .bc files for libraries instead of .a files, which causes link errors I try to link my project. How can I get Boost to generate .a files? (Emscripten uses .a files for libraries: https://emscripten.org/docs/compiling/Building-Projects.html#using-libraries) -- Rainer Deyke (rainerd(a)eldwood.com)

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Cannot build 1.76.0 for Windows (wrong path to compiler)
by Andreas Tscharner 22 Apr '21

22 Apr '21

Hello World, I try, according to the "Get started guide" >bootstrap.bat in the main boost directory. I get an error, because "C:\Program Files(x86)" ... contains a space and is not double quoted. So I replace all set "B2_CXX=%CXX% ..." with set "B2_CXX="%CXX%" ..." in tools\build\src\engine\config_toolset.bat After that I have the following problem: D:\Projects\development\QUARTIS-related\boost>.\bootstrap.bat Building Boost.Build engine LOCALAPPDATA=C:\Users\ATs\AppData\Local Found with vswhere C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise Found with vswhere C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise Call_If_Exists "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\Common7\Tools\..\..\VC\Auxiliary\Build\vcvarsall.bat" AMD64 ********************************************************************** ** Visual Studio 2019 Developer Command Prompt v16.9.4 ** Copyright (c) 2021 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' ### ### Using 'vc142' toolset. ### D:\Projects\development\QUARTIS-related\boost\tools\build\src\engine>"C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Tools/MSVC/14.27.29110/bin/Hostx64/x64/cl.exe" /nologo /MP /MT /TP /Feb2 /wd4996 /O2 /GL /EHsc -DNDEBUG builtins.cpp class.cpp command.cpp compile.cpp constants.cpp cwd.cpp debug.cpp debugger.cpp execcmd.cpp execnt.cpp filent.cpp filesys.cpp frames.cpp function.cpp glob.cpp hash.cpp hcache.cpp hdrmacro.cpp headers.cpp jam.cpp jamgram.cpp lists.cpp make.cpp make1.cpp md5.cpp mem.cpp modules.cpp native.cpp object.cpp option.cpp output.cpp parse.cpp pathnt.cpp pathsys.cpp regexp.cpp rules.cpp scan.cpp search.cpp jam_strings.cpp startup.cpp subst.cpp sysinfo.cpp timestamp.cpp variable.cpp w32_getreg.cpp modules/order.cpp modules/path.cpp modules/property-set.cpp modules/regex.cpp modules/sequence.cpp modules/set.cpp /link kernel32.lib advapi32.lib user32.lib Das System kann den angegebenen Pfad nicht finden. It tries to start "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Tools/MSVC/14.27.29110/bin/Hostx64/x64/cl.exe". Unfortunately at my system, I don't have this path. I have C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.28.29910... Please note the different number after "MSVC" What is the problem? How can I fix this? TIA and best regards Andreas -- ("`-''-/").___..--''"`-._ `o_ o ) `-. ( ).`-.__.`) (_Y_.)' ._ ) `._ `. ``-..-' _..`--'_..-_/ /--'_.' .' (il).-'' (li).' ((!.-' Andreas Tscharner andy(a)stupidmail.ch ICQ-No. 14356454

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Reminder: BinTray is shutting down 1-May
by Marshall Clow 21 Apr '21

21 Apr '21

Bintray is “sunsetting” on the 1st of May. At that time, you will be unable to download boost releases from there. Before that time, their service will be occasionally interrupted. We will be updating the web site before then, but the new location is: https://boostorg.jfrog.io/artifactory/main/release/ <https://boostorg.jfrog.io/artifactory/main/release/> So instead of downloading from: https://dl.bintray.com/boostorg/release/1.76.0/source/boost_1_76_0.tar.gz You should download from: https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76… This applies to all releases from 1.63.0 onward — Marshall

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Boost Graph + Compute Libraries
by Muhammad Hassan Khan 20 Apr '21

20 Apr '21

Hi, I am new to boost libraries. I was wondering if I can use boost graph and boost compute libraries in one code to implement graphs on GPUs. Can you give any example if it is possible? or any other solution to it. Thank you. Regards, Hassan Khan

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ASIO: acceptor::async_accept throws "Operation cancelled" after restart io_service
by Joost Kraaijeveld 19 Apr '21

19 Apr '21

Hi, In short my program: - creates an io_service - calls acceptor::async_accept - calls io_service.run - handle several connections OK - calls io_service.stop - the acceptor goes out of scope (i.e. the destructor of the owning object is ran) - calls io_service.restart - calls acceptor::async_accept which then throws "Operation cancelled" Should it be possible to do this? When/under what circumstances does async_accept throw this exception? Could it be connected with the fact that the acceptor's destructors documents that is does some cleanup but actually does nothing, from the source: /// Destroys the acceptor. /** * This function destroys the acceptor, cancelling any outstanding * asynchronous operations associated with the acceptor as if by calling * @c cancel. */ ~basic_socket_acceptor() { } OS: Linux Debian Bullseye, Boost 1.74, gcc 10 TIA Joost

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[release] Boost 1.76.0
by Marshall Clow 17 Apr '21

17 Apr '21

Release 1.76.0 of the Boost C++ Libraries is now available. These open-source libraries work well with the C++ Standard Library, and are usable across a broad spectrum of applications. The Boost license encourages both commercial and non-commercial use. This release contains no new libraries and numerous enhancements and bug fixes for existing libraries. For details, including download links, see <http://www.boost.org/users/news/version_1.76.0> You can also download directly from: <https://boostorg.jfrog.io/artifactory/main/release/1.76.0/> To install this release on your system, see <http://www.boost.org/doc/libs/release/more/getting_started/index.html> Thanks to everyone who participated in this release. Thanks, -- The Boost Release Team Marshall Clow, Michael Caisse, Glen Fernandes

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Boost.Test - test tree is empty
by Olaf Peter 17 Apr '21

17 Apr '21

Hello, I am in despair. The attached source compiles fine, but gives: $ bin/utf_dataset_loader_issue Test setup error: test tree is empty and I don't know why. It is based [Data-driven test cases parametrized from the command line <https://www.boost.org/doc/libs/1_73_0/libs/test/doc/html/boost_test/runtime…>](https://www.boost.org/doc/libs/1_73_0/libs/test/doc/html/boost_test/runtime_config/custom_command_line_arguments.html#boost_test.runtime_config.custom_command_line_arguments.data_driven_test_cases_parametri) but reduced to pure API, no cli parse, file loading etc. Any help is appreciated.

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