September 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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[Boost.Asio] Segmentation fault when ::getaddrinfo() returns EAI_SYSTEM without system error code set (errno = 0) - is this a bug?
by Nils Frielinghaus 04 Oct '21

04 Oct '21

Hello Boost users, I experienced a segmentation fault inside Boost in the following scenario: o There was an illegal DNS entry o When resolving that illegal DNS entry on a Yocto-based embedded Linux distribution, ::getaddrinfo() returned with the error code EAI_SYSTEM but errno was set to 0 o The function translate_addrinfo_error(int) in boost/asio/detail/impl/socket_ops.ipp translates this into boost::system::error_code(0, boost::asio::error::get_system_category()) o This is then interpreted as a success by the calling function and the other output parameters of ::getaddrinfo() are accessed which resulted in the segmentation fault My question would be whether this should be considered a bug in the Boost ASIO library? One could argue that the system should not return EAI_SYSTEM with errno not being set properly. But one could also argue that returning EAI_SYSTEM indicates that something went wrong and that the output parameters are not to be accessed. Nils ------ Nils Frielinghaus

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Problem understanding 'boost::intrusive::list_member_hook<>'
by John Emmas 14 Sep '21

14 Sep '21

I'm in the early stages of trying to understand boost::intrusive::list' so forgive me if I'm just doing something stupid!! Using VS2019 I wrote a small demo app which uses 'boost::intrusive::list_base_hook<>':- #include <boost/intrusive/list.hpp> #include <string> #include <iostream> using namespace std; class animal : public boost::intrusive::list_base_hook<> { public: animal (string n, int l) : name{move(n)}, legs{l} {} string name; int legs; }; using animal_list = boost::intrusive::list<animal>; template<typename T> void print_list (const boost::intrusive::list<T>& elem) { for (const T& a : elem) cout << "A " << a.name << " has " << a.legs << " legs" << '\n'; } int main() { animal a1{"dog", 4}; animal a2{"spider", 6}; animal a3{"budgie", 2}; animal_list animals; animals.push_back(a1); animals.push_back(a2); animals.push_back(a3); print_list (animals); return 0; } Everything runs fine and I see the expected output but I've noticed that some other developers use something called a 'list_member_hook' rather than my 'list_base_hook' - so class animal would look like this:- class animal { public: animal (string n, int l) : name{move(n)}, legs{l} {} string name; int legs; boost::intrusive::list_member_hook<> _animal_hook; }; and then later on in the program there'd be a couple of lines looking something like this:- typedef boost::intrusive::member_hook<animal, boost::intrusive::list_member_hook<>, &animal::_animal_hook> AnimalHookOption; typedef boost::intrusive::list<animal, AnimalHookOption> Animals; But when I try that here, VS2019 throws up this compiler error:- error C2039: 'default_list_hook': is not a member of 'animal' Can anyone explain what I'm doing wrong?? John

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Support end date of boost version ,1.76.0
by rajesh daggumati 08 Sep '21

08 Sep '21

Hi Team, When is supporting end date for boost 1.76.0. Please let me know asap. Regards, Rajesh D

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Linking Problem
by Stephen P. Molnar 04 Sep '21

04 Sep '21

I have successful compiled an application on my Debian-10 platform using boost-1-67. It is an essential part of my computations chemistry pipe line. Now Debian 11 has been released. I have installed it in a VM in order to make sure that the app is compilable in Debian 11 with boost-1-74 (the Debian12 version of boost), before upgrading my Linux platform. I installed boost in /user/ilocal. The makefile is: BASE=/usr/local BOOST_VERSION=1_74_0 BOOST_INCLUDE = $(BASE)/include C_PLATFORM= -pthread GPP=g++ C_OPTIONS= -O3 -DNDEBUG BOOST_LIB_VERSION= include ../../makefile_common The test compile went well until the link stage. The process stopped with: g++ -pthread -ansi -Wno-long-long -O3 -DNDEBUG -I /usr/local/include -L/usr/local/lib -L. -o gwovina main.o cache.o coords.o current_weights.o everything.o grid.o szv_grid.o manifold.o model.o gwo.o gwo_mutate.o my_pid.o naive_non_cache.o non_cache.o parallel_gwo.o parse_pdbqt.o pdb.o quasi_newton.o quaternion.o random.o ssd.o terms.o weighted_terms.o rotamer.o -l boost_system -l boost_thread -l boost_program_options /usr/bin/ld: cannot find -lboost_system /usr/bin/ld: cannot find -lboost_thread /usr/bin/ld: cannot find -lboost_program_options collect2: error: ld returned 1 exit status make: *** [../../makefile_common:34: gwovina] Error 1 Even my limited knowledge (my original programming experience was with FORTRAN II in the early 1960's), I can see the the problem. Unfortunately, I don't know the solution. Assistance will be greatly appreciated. Thanks om advance. -- Stephen P. Molnar, Ph.D. www.molecular-modeling.net 614.312.7528 (c) Skype: smolnar1

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Comment on divide_unsigned_helper
by Neill Clift 03 Sep '21

03 Sep '21

Hi, I was trying to understand the algorithm inside the main divide routine. I struggled with this bit of code: if ((prem[r_order] <= py[y_order]) && (r_order > 0)) { double_limb_type a = (static_cast<double_limb_type>(prem[r_order]) << CppInt1::limb_bits) | prem[r_order - 1]; double_limb_type b = py[y_order]; double_limb_type v = a / b; if (v <= CppInt1::max_limb_value) { guess = static_cast<limb_type>(v); --r_order; } } I was trying to understand why we essential set guess to 1 in the case that the division is too big. I finally realized that the only way we can have v > CppInt1::max_limb_value is if we have prem[r_order] == py[y_order]. Some simple inequalities with floor can convince you of this. So in the case of equality we do an expensive divide and test when we could move the test outside like this: limb_type guess = 1; if (r_order == 0) { <-------- do this first to simplify guess = prem[0] / py[y_order]; } else if (prem[r_order] == py[y_order]) { <----------- handle it here to avoid the divide guess = 1; ... This leads to another question. Why is this line: guess = prem[0] / py[y_order]; not this line: guess = prem[0] / py[0]; Logically for division it must be the second line. In fact this loop has the invariant that r_order >= y_order. That makes sense for division. So the divisor must be py[0]. That suggests a divisor with one element and we handle that case via a special divide. So that code is not needed I believe. We end up with this: BOOST_ASSERT(r_order >= y_order && y_order >= 1); if (prem[r_order] == py[y_order]) { guess = 1; } else if (prem[r_order] < py[y_order]) { double_limb_type a = (static_cast<double_limb_type>(prem[r_order]) << CppInt1::limb_bits) | prem[r_order - 1]; double_limb_type b = py[y_order]; double_limb_type v = a / b; BOOST_ASSERT(v <= CppInt1::max_limb_value); guess = static_cast<limb_type>(v); --r_order; } else { double_limb_type a = (static_cast<double_limb_type>(prem[r_order]) << CppInt1::limb_bits) | prem[r_order - 1]; double_limb_type b = (y_order > 0) ? (static_cast<double_limb_type>(py[y_order]) << CppInt1::limb_bits) | py[y_order - 1] : (static_cast<double_limb_type>(py[y_order]) << CppInt1::limb_bits); BOOST_ASSERT(b); double_limb_type v = a / b; guess = static_cast<limb_type>(v); } BOOST_ASSERT(guess); // If the guess ever gets to zero we go on forever.... Some simple random divide tests seem to show a little over 2% improvement from doing this. Of course this could just be code layout changes. Just thinking that the 64 bit values are random would make me think this case is rare but I guess we subtract out multiples of the divisor and cause this to happen more for reasons that are hard to understand (for me anyway). I see the path hit a lot. Neill.

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Jamshell query
by Mohammed Zahid 03 Sep '21

03 Sep '21

Hi, I am trying to run boost build in distributed environment by setting JAMSHELL I tried setting as environment variable and passing as command line variable -sJAMSHELL= Both didn't work https://github.com/bfgroup/b2/discussions/78 Need you guidence on how to do it. Thanks, Mohammed zahid

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3D Tree Queries
by Glenn, Rachel M 02 Sep '21

02 Sep '21

I have a question about 3D RTree spatial queries, like a cube, sphere, or something. Are there any examples of how that can be done? I know how to do it for 2D RTree. Do you recommend the regular RTREE or a is there another one to use, like an rstar, that would be better? Thanks, Rachel

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