I am trying to transmit a class of of unknown subclass, but known base class.
I believe this should be possible using boost::serialization, BOOST_CLASS_EXPORT_GUID and boost::mpi, but I'm pretty new to C++ in general
This is the code that I have:
#include <boost/mpi.hpp>
#include <boost/mpi/environment.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/serialization/string.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/vector.hpp>
#include <iostream>
namespace mpi = boost::mpi;
class Action {
protected:
int start_rank;
std::string greeting;
Action(std::string greeting) {
mpi::communicator world;
this->start_rank = world.rank();
this->greeting = greeting;
};
private:
friend class boost::serialization::access;
template<class Archive> void serialize(Archive &ar, const unsigned int version) {
ar & this->start_rank;
ar & this->greeting;
};
public:
Action() = default;
void invoke() {
mpi::communicator world;
std::cout << this->greeting << "! I am process " << world.rank() << " of " << world.size()
<< ". I was created on " << this->start_rank << "." << std::endl;
};
};
class HelloAction : public Action {
public:
HelloAction() : Action("Hello") {};
};
class GoodByeAction : public Action {
public:
GoodByeAction() : Action("Good bye") {};
};
BOOST_CLASS_EXPORT_GUID(Action, "Action");
BOOST_CLASS_EXPORT_GUID(HelloAction, "HelloAction");
BOOST_CLASS_EXPORT_GUID(GoodByeAction, "GoodByeAction");
int main() {
mpi::environment env;
mpi::communicator world;
HelloAction *hello = new HelloAction();
mpi::broadcast(world, hello, 0);
hello->invoke();
GoodByeAction *bye = new GoodByeAction();
mpi::broadcast(world, bye, 1);
bye->invoke();
world.barrier();
if (world.rank() == 0) {
std::cout << "sending unknown action classes!" << std::endl;
HelloAction *yup = new HelloAction();
boost::mpi::packed_oarchive oar(world);
oar << yup;
}
else {
std::cout << "receiving unknown action classes!" << std::endl;
Action *action = NULL;
boost::mpi::packed_iarchive iar(world);
iar >> action;
action->invoke();
}
return 0;
}
compiling/running with:
mpic++ -g -std=c++1y hello.cpp -lboost_serialization -lmpi -lboost_mpi
mpiexec -np 2 ./a.out
This seems to run just fine:
Hello! I am process 0 of 2. I was created on 0.
Hello! I am process 1 of 2. I was created on 0.
Good bye! I am process 1 of 2. I was created on 1.
Good bye! I am process 0 of 2. I was created on 1.
... until getting to the "sending/receiving of unknown action classes", where I get runtime errors:
receiving unknown action classes!
sending unknown action classes!
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::mpi::exception> >'
what(): MPI_Unpack: MPI_ERR_ARG: invalid argument of some other kind
[machine-name:20194] *** Process received signal ***
[machine-name:20194] Signal: Aborted (6)
[machine-name:20194] Signal code: (-6)
[machine-name:20194] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x352f0) [0x7fa685cc22f0]
[machine-name:20194] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x37) [0x7fa685cc2267]
[machine-name:20194] [ 2] /lib/x86_64-linux-gnu/libc.so.6(abort+0x16a) [0x7fa685cc3eca]
[machine-name:20194] [ 3] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZN9__gnu_cxx27__verbose_terminate_handlerEv+0x16d) [0x7fa6862fdb7d]
[machine-name:20194] [ 4] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x8d9c6) [0x7fa6862fb9c6]
[machine-name:20194] [ 5] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x8da11) [0x7fa6862fba11]
[machine-name:20194] [ 6] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x8dc29) [0x7fa6862fbc29]
[machine-name:20194] [ 7] ./a.out(_ZN5boost15throw_exceptionINS_3mpi9exceptionEEEvRKT_+0x80) [0x41426d]
[machine-name:20194] [ 8] ./a.out() [0x413802]
[machine-name:20194] [15] ./a.out() [0x4306e6]
[machine-name:20194] [16] /usr/lib/x86_64-linux-gnu/libboost_serialization.so.1.58.0(_ZN5boost7archive6detail19basic_iarchive_impl12load_pointerERNS1_14basic_iarchiveERPvPKNS1_25basic_pointer_iserializerEPFS9_RKNS_13serialization18extended_type_infoEE+0x4d) [0x7fa686df5b8d]
[machine-name:20194] [17] ./a.out() [0x41d08d]
[machine-name:20194] [23] ./a.out() [0x40d293]
[machine-name:20194] [24] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0) [0x7fa685cada40]
[machine-name:20194] [25] ./a.out() [0x40cfc9]
[machine-name:20194] *** End of error message ***
--------------------------------------------------------------------------
mpiexec noticed that process rank 1 with PID 20194 on node machine-name exited on signal 6 (Aborted).
--------------------------------------------------------------------------
Questions:
boost, should it be possible to transmit an unknown subclass at all with or without boost? I understand I could have a registration of sorts by string name, and an inversion of control guy to handle creation, but I thought that was the intent of BOOST_CLASS_EXPORT_GUID.boost) to make this work with regular ol' MPI?You are quite close: Firstly your are missing the actual communication functions for the packed archives. You are trying to extract from the packed_iarchive without having received anything into that archive. For instance, you can use broadcast as described:
with packed archives, the root sends a packed_oarchive [...] whereas the other processes receive a acked_iarchive [...].
However, simply adding the calls to your example will instantiate an Action instead of a HelloAction. It takes a bit more effort:
HelloAction* and then unserialize an Action*, regardless whether it is a virtual class1. If you have to use Action* in both cases, you of course also have to use virtual classes, so that boost actually knows the runtime type. Technically you can serialize an Action* to a HelloAction Object, and then deserialize an Action* that yiels the sliced Action-part of the original. Again, this works for your example, but it fails for more complex ones and thus is not a good idea.serialize for the sub classes as well1.Putting it all together a working example looks like this: Note: I added a bit more output to verify that objects are created with the correct types.
#include <boost/mpi.hpp>
#include <boost/mpi/environment.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/serialization/string.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/vector.hpp>
#include <iostream>
namespace mpi = boost::mpi;
class Action {
protected:
int start_rank;
std::string greeting;
Action(std::string greeting) {
mpi::communicator world;
std::cout << world.rank() << ": Creating a Action: " << greeting << std::endl;
this->start_rank = world.rank();
this->greeting = greeting;
};
private:
friend class boost::serialization::access;
template<class Archive> void serialize(Archive &ar, const unsigned int version) {
ar & this->start_rank;
ar & this->greeting;
};
public:
virtual ~Action() = default;
Action() {
mpi::communicator world;
std::cout << world.rank() << ": Creating a naked Action" << std::endl;
}
void invoke() {
mpi::communicator world;
std::cout << this->greeting << "! I am process " << world.rank() << " of " << world.size()
<< ". I was created on " << this->start_rank << "." << std::endl;
};
};
class HelloAction : public Action {
public:
HelloAction() : Action("Hello") {
mpi::communicator world;
std::cout << world.rank() << ": Creating an HelloAction" << std::endl;
}
template<typename Archive>
void serialize(Archive & ar, const unsigned int file_version) {
ar & boost::serialization::base_object<Action>(*this);
}
};
class GoodByeAction : public Action {
public:
GoodByeAction() : Action("Good bye") {
mpi::communicator world;
std::cout << world.rank() << ": Creating an GoodByeAction" << std::endl;
}
template<typename Archive>
void serialize(Archive & ar, const unsigned int file_version) {
ar & boost::serialization::base_object<Action>(*this);
}
};
// It is totally fine to use the EXPORT (without GUID) for MPI
BOOST_CLASS_EXPORT(GoodByeAction)
BOOST_CLASS_EXPORT(HelloAction)
int main() {
mpi::environment env;
mpi::communicator world;
HelloAction *hello = new HelloAction();
mpi::broadcast(world, hello, 0);
hello->invoke();
GoodByeAction *bye = new GoodByeAction();
mpi::broadcast(world, bye, 1);
bye->invoke();
world.barrier();
if (world.rank() == 0) {
std::cout << "sending unknown action classes!" << std::endl;
Action *yup = new HelloAction();
boost::mpi::packed_oarchive oar(world);
oar << yup;
mpi::broadcast(world, oar, 0);
}
else {
std::cout << "receiving unknown action classes!" << std::endl;
boost::mpi::packed_iarchive iar(world);
mpi::broadcast(world, iar, 0);
Action *action = nullptr;
iar >> action;
std::cout << "RTTI: " << typeid(*action).name() << std::endl;
action->invoke();
}
return 0;
}
Regarding plain old MPI: Sounds like reinventing the wheel to me - certainly possible but not necessarily desirable.
1 I can't find a definite statement about that in the documentation. This is based on things go horribly wrong if you try otherwise. I would appreciate a comment / better answer regarding this.