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Implementing python's enumerate with iterator adaptors
by Jens Auer 18 Apr '12

18 Apr '12

Hi, I am implementing something similar to python's enumerate using boost iterator adapter, but I am running into two problems I am unable to solve. Both problems use my Enumerate-adaptor defined as: #include <utility> #include <boost/iterator/iterator_adaptor.hpp> namespace Iterator { // some simple wrapper to have better names than std::pair template<typename T, typename X> struct Enumerated { Enumerated(T i, X x): count(i), value(x) { } T count; X value; }; template< typename Iterator, typename T = typename Iterator::difference_type> class Enumerator: public boost::iterator_adaptor<Enumerator<Iterator, T>, Iterator, Enumerated<T, typename Iterator::value_type>, boost::use_default, Enumerated<T, typename Iterator::reference> > { public: Enumerator(): mCount(), mPos(), mStep() { } template<typename It> explicit Enumerator(It i, T start=T(), T step=T(1) ): mCount(start), mPos(i), mStep(step) { } private: friend class boost::iterator_core_access; Enumerated<T, typename Iterator::reference > dereference() const { return Enumerated<T, typename Iterator::reference >(mCount, *mPos); } Enumerated<T, typename Iterator::reference > dereference() { return Enumerated<T, typename Iterator::reference >(mCount, mPos); } bool equal(Enumerator<Iterator, T> const& other) const { return mPos == mPos; } void increment() { mCount += mStep; mPos += 1; } void decrement() { mCount -= mStep; mPos -= 1; } void advance(typename Iterator::difference_type step) { mCount += step * mStep; mPos += step; } typename Iterator::difference_type distance_to(Enumerator<Iterator, T> const& other) const { return std::distance(mPos, other.mPos); } T mCount; Iterator mPos; typename Iterator::difference_type mStep; }; template<typename Iterator, typename T> Enumerator<Iterator, T> enumerate(Iterator i, T start=0, T step=1) { return Enumerator<Iterator, T>(i, start, step); } When I compile the following sample program, msvc (VS2010) prints an error, but g++ does not have any problems. #include <vector> #include <iostream> #include <algorithm> void foo() { std::vector<int> v; auto i = Iterator::enumerate(v.begin(), 0, 1); auto j = Iterator::enumerate(v.end(), 0, 1); std::for_each( i, j, [](decltype(*i) e) { std::cout << e.count << ", " << e.value << std::endl; }); } Error 1 error C2665: 'std::_Debug_range2' : none of the 2 overloads could convert all the argument types d:\programme\microsoft visual studio 10.0\vc\include\xutility 728 My second problem can be reproduced with the following sample program on both msvc and g++: #include <vector> #include <iostream> #include <algorithm> void foo() { std::vector<int> v; auto i = Iterator::enumerate(v.begin(), 0, 1); auto y = i->count; auto z = i->value; } MSVC: Error 3 error C2664: 'boost::implicit_cast' : cannot convert parameter 1 from 'Iterator::Enumerated<T,X> *' to 'boost::detail::operator_arrow_proxy<T>' c:\software development\externals\include\boost\iterator\iterator_facade.hpp 326 G++: In file included from /usr/include/boost/iterator/iterator_adaptor.hpp:15:0, from Enumerate.h:18, from Enumerate.cpp:1: /usr/include/boost/iterator/iterator_facade.hpp: In static member function 'static boost::detail::operator_arrow_result<ValueType, Reference, Pointer>::type boost::detail::operator_arrow_result<ValueType, Reference, Pointer>::make(Reference) [with ValueType = Iterator::Enumerated<int, int>, Reference = Iterator::Enumerated<int, int&>, Pointer = Iterator::Enumerated<int, int>*, boost::detail::operator_arrow_result<ValueType, Reference, Pointer>::type = boost::detail::operator_arrow_proxy<Iterator::Enumerated<int, int> >]': /usr/include/boost/iterator/iterator_facade.hpp:648:49: instantiated from 'boost::iterator_facade<I, V, TC, R, D>::pointer boost::iterator_facade<I, V, TC, R, D>::operator->() const [with Derived = Iterator::Enumerator<__gnu_cxx::__normal_iterator<int*, std::vector<int> >, int>, Value = Iterator::Enumerated<int, int>, CategoryOrTraversal = boost::random_access_traversal_tag, Reference = Iterator::Enumerated<int, int&>, Difference = int, boost::iterator_facade<I, V, TC, R, D>::pointer = boost::detail::operator_arrow_proxy<Iterator::Enumerated<int, int> >]' Enumerate.cpp:27:14: instantiated from here /usr/include/boost/iterator/iterator_facade.hpp:327:49: error: no matching function for call to 'implicit_cast(Iterator::Enumerated<int, int&>*)' Any help would be greatly appreciated, Bets regards, Jens

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Stack objects and polymorphic access
by asif saeed 18 Apr '12

18 Apr '12

Hi, I want to maintain stack semantics in my application and avoid heap. For very few requirements, I have to write polymorphic code but I still want to create objects on stack and want to assign their addresses to some abstract base class for polymorphic access. So, all stack variables will be destroyed at the end of their scope and, yet, I'll get polymorphic access. However, functions creating/returning concrete objects have concrete class types. Can boost help me here? Best regards, Asif

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thread safety of shared_ptr
by Yuanlong Shao 18 Apr '12

18 Apr '12

Hi all, If I do the following ---------------------------------------------------------------------------------------------------------- shared_ptr<int> pA( new int(1) ); shared_ptr<int> pB( new int(2) ); shared_ptr<int> pNew( new int(3) ); // thread A pA = pB; // thread B pB = pNew; ---------------------------------------------------------------------------------------------------------- I know that whether pA will be int(2) or int(3) after execution is undefined, but if I do want to do this no matter what value of pA I get, will this cause atomicity problem? I mean, thread A increases counter for int(2), but thread B decrease it, is this thread safe? Yuanlong Shao

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Troubles using boost::circular_buffer
by Ted Byers 17 Apr '12

17 Apr '12

I declare I use it: #include <boost/circular_buffer.hpp> I make my function: double calculateStdDev(const boost::circular_buffer<double>& input, double& mean, double& variance, double& stddev) { if (input.empty()) return 0.0; boost::circular_buffer<double>::const_iterator it = input.begin(), end = input.end(); double M = *it; double Q = 0.0; unsigned int count = 1; ++it; while (it != end) { unsigned int k = count; ++count; double del = *it - M; unsigned int j = k + 1; Q += k * (del * del) / j; M += del / j; ++it; } variance = Q / (count - 1); stddev = std::sqrt(variance); mean = M; return stddev; } This function doesn't need to know are care about the number of items in the buffer. It just makes one pass through the data, from it = inut.begin() to input.end(). This particular algorithm, BTW, provides a solution that is MUCH faster and much more accurate in some cases, than the two pass algorithm, and is much more accurate than the other single pass algorithms you may see recommended. But that isn't the point. In the header that provides the prototypes for the functions in this particular CPP file, I have: double calculateStdDev(const boost::circular_buffer<double>& input, double& mean, double& variance, double& stddev); And gcc v 4.3.4 gives me the following error: ../../include/distribution.moments.hpp:9: error: wrong number of template arguments (1, should be 2) /usr/local/include/boost/circular_buffer/base.hpp:70: error: provided for 'template<class T, class Alloc> class boost::circular_buffer' I am not sure I understand why. Does this mean that I have to make calculateStdDev a template function? E.g.: template <typename T> double calculateStdDev(const boost::circular_buffer<double, T>& input, double& mean, double& variance, double& stddev) { // and put the entire implementation here in the header instead of in the cpp file with the overloads for other types such as std::vector) } But, if that is the case, why is it possible to instantiate such a buffer using the following (as in the example)? boost::circular_buffer<int> cb(3); I must have missed something, but I don't know what. Cheers Ted

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[MSM] a timer/timeout for the whole state machine (including submachines)
by Albert Gil Moreno 17 Apr '12

17 Apr '12

Hi, I've been working for a while with the MSM and I'm very impressed about it... congratulations for your work!! I've to say that I'm not an expert on UML nor state machines and I think that my needs are a very common user-case... so I'm probably missing something! Basically what I need is a (reusable) Timer that, after a number of Clocks, it sends a TimeOut to the state machine, and when the Timer receives a Reset it restarts the counting of clocks. (I want to also add a Pause or similar but this doesn't matter right now...) So, the goal is that any (or all) of my states could be controlled by the Timer and if no events are received for a while a TimeOut will be (always) received/processed. AFAIK there is no concept of timer/timeout in the MSM, but I found very straightforward to implement my idea with an Orthogonal Region with a single state Timer that receives Clock and Reset events and sends a TimeOut. And it worked like a charm!! But I found a problem with one of my states become a submachine... The Timer::Reset action executes a fsm.process_event(Timer::Reset()), but this event is not processed. I realized that "fsm" is the submachine and AFAIK there is no way to access to the parent(est) fsm... So, is there a better or more standard way to implement a Timer/Timeout in UML/MSM? And, although "fsm" is the submachine, why the no_transition function is not executed (this last seems a bug to me...). Albert PD: Do you think that has meaning that the MSM could have an "on_timeout" function for the states (like on_entry/exit?), or to have a timeout event like "none"... ok may be this sounds huge to implement and not so generic...

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Questions about packaged_task , Promise and serialization of a class object and event handling
by Master 16 Apr '12

16 Apr '12

Hello all again . i have couple of questions again which i would appreciate any kind of help and answer, my first question is about packaged_task and how we can use it , i mean i tried using packaged_task with functions , with parameters , and i got errors doing it . so do we always have to use class or stcucts in order for us to use packaged_task ? how can i send some arguments to a function when im trying to make a package out of ? i have done the packaging with parameterelss functions , but i dont know how im supposed to pass parameters ! : here is my application working with parameterless functions . > //in the name of GOD > //Seyyed Hossein Hasan Pour > //Learning Boost- How Threading works in Boost > //How to pass parameters to functions in packaged_task > #define BOOST_THREAD_USE_LIB > #include <iostream> > #include <cstdlib> > #include <boost/thread.hpp> > #include <boost/date_time/posix_time/posix_time.hpp> > using namespace std; > > vector<int> SharedResource; > boost::shared_mutex sharedMutex; > > int FillSharedResource() > { > int numberOfItems=10; > for (int i = 0; i< numberOfItems; i++) > { > boost::unique_lock<boost::shared_mutex> lock(sharedMutex); > SharedResource.push_back(i); > lock.unlock(); > } > return 10; > } > > int Print1() > { > for (int i = 0; i< SharedResource.size(); i++) > { > boost::this_thread::sleep(boost::posix_time::seconds(1)); > boost::lock_guard<boost::shared_mutex> locker(sharedMutex); > cout<<boost::this_thread::get_id()<<"\tItem: > "<<SharedResource[i]<<endl; > } > return 101; > } > > int Print2() > { > for (int i = 0; i< SharedResource.size(); i++) > { > boost::this_thread::sleep(boost::posix_time::seconds(1)); > boost::lock_guard<boost::shared_mutex> locker(sharedMutex); > cout<<boost::this_thread::get_id()<<"\tItem: > "<<SharedResource[i]<<endl; > } > return 102; > } > > int main() > { > > boost::packaged_task<int> > pkg0(FillSharedResource), > pkg1(Print1), > pkg2(Print2); > > boost::thread > t0(ref(pkg0)), > t1(ref(pkg1)), > t2(ref(pkg2)); > > boost::unique_future<int> > f0(pkg0.get_future()), > f1(pkg1.get_future()), > f2(pkg2.get_future()); > > std::cout<< f0.get()<<"\n"<< f1.get()<< "\n"<< f2.get(); > > system("pause"); > return 0; > } > ------------------------- can someone show me a simple sample of using Promise in threading ? i mean i already know about future , whats the need for Promise ? ! -------------------------- whats the different between read_some and async_read_some ? in asio ? -------------------------- i know that when i need to send an argument to event handler ( signal ) , i frist should declare sth like this : > *boost::signal2::signal <function-return-type (paramerter type)> mysignal > ;* > *mysignal**.connect(myfunc,my-functions-argumant)*; > *mysignal**.connect(myfunc2,my-function2s-argumant)*; > now if i have couple of functions with the same signature , doing different jobs with different arguments , how can i give their respective arguments ? i mean at the moment , i can only write : mysignal(5);! and this passes 5 to all functions connected with this signal! do i really have to make one signal for each functions ?so that i can pass different and yet with the same type argument to different functions using one signal . is'nt there any other way around it ? if inside a signal , i run a thread and then i block that signal using signal.block , would that block that thread too ? and then unblocking it would it unblock that thread too ? is it safe doing this ? --------------------------- why do we use function names with const that the end of it ? i mean sth like this : > void operator()() const > { > } > or > void boostFunctionName(sth) const > { > } > what is that const for ? what does it declare ? why is it necessary to use it that way ? -------------------- how do i serialize a class of mine ? i mean i read that if i have vector , i need to use some functions , if i have foo i need another function ! what exactly do you serialize your classes ? i mean maybe i have std::string , char , vectors of some kind , and a self made class or type used in my class to be serialized , how should i go about it . any guidance is greatly appreciated . --------------------- i tired to use boost::container::vector for storing my threads , and it went just fine . but i have a problem in determining which thread is which , i mean i already found out that i can use if-else for this matter , but since i used a vector , and the number of threads being created at run-time is not known , so i need to use a for statement so that i can iterate throuh all of th evectors items and then if i find a match , i do as i wish . the problem is , when i try to have sth like this , it fails : > boost::id id = myvect[0] > i want to pass this id for matching operation ( or declare it as global ) , what am i missing again ? another problem i have in this regard is that , when i store my threads in a lets say vector just like the sample i gave earlier , it is not guaranteed that threads inside that vector actually points to a legal thread of execution by the time i go to check for sth .!( i mean there is a good chance that they already ran and got terminated!) seemingly i can not use joinable to see if i am dealing with an active or lets say legitimate thread ! , my question is , how can i check to see if an object of type thread , actually points to sth real ? how to check that ? --------------------- when i try to compile source codes using Asio using MingW , i get linking errors ! what is the cause and how can i fix that ? i get the errors: > C:\boost_1_49_0\boost\asio\detail\impl\winsock_init.ipp|39|undefined > reference to `WSAStartup@8'| > C:\boost_1_49_0\boost\asio\detail\impl\winsock_init.ipp|48|undefined > reference to `WSACleanup@0'| > Thank you all in advance Seyyed Hossein Hasan Pour

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Problem with asych_write() when sending more than 65536 bytes data on Solaris
by Ranadheer 16 Apr '12

16 Apr '12

We are observing one weird problem when sending message of size more than 65536 bytes using boost asynch_write on Solaris (though the problem is not observed on Linux). We are using boost version 1.47 with studio 12 CC compiler (on Solaris) and g++ 4.4.3 (on Linux). When a message of size more than 65536 (sometimes we are observing the issue with around 50K bytes size also but with 65536 bytes the issue is always reproducible) is sent, the message is delivered correctly to the receiver. But once the message is sent, the io service thread on the sender side goes into busy-wait loop. "truss" on the sender pid shows the following calls continuously. /6: recvmsg(57, 0xFFFFFD7FEB9FDDF0, 0) Err#11 EAGAIN /6: write(13, " 9\0\0\019\0\0\0", 8) = 8 /6: ioctl(13, DP_POLL, 0xFFFFFD7FEB9FE460) = 1 /6: recvmsg(57, 0xFFFFFD7FEB9FDDF0, 0) Err#11 EAGAIN /6: write(13, " 9\0\0\019\0\0\0", 8) = 8 /6: ioctl(13, DP_POLL, 0xFFFFFD7FEB9FE460) = 1 /6: recvmsg(57, 0xFFFFFD7FEB9FDDF0, 0) Err#11 EAGAIN /6: write(13, " 9\0\0\019\0\0\0", 8) = 8 /6: ioctl(13, DP_POLL, 0xFFFFFD7FEB9FE460) = 1 /6: recvmsg(57, 0xFFFFFD7FEB9FDDF0, 0) Err#11 EAGAIN /6: write(13, " 9\0\0\019\0\0\0", 8) = 8 /6: ioctl(13, DP_POLL, 0xFFFFFD7FEB9FE460) = 1 /6: recvmsg(57, 0xFFFFFD7FEB9FDDF0, 0) Err#11 EAGAIN /6: write(13, " 9\0\0\019\0\0\0", 8) = 8 /6: ioctl(13, DP_POLL, 0xFFFFFD7FEB9FE460) = 1 "lsof" shows that the socket descriptor 57 above is the socket descriptor corrected to the receiver. Thread 6 here is the ioservice thread whose stack trace is - thread t@6 -- ???????? thread_proxy boost::detail::thread_data<>::run des::tunnel::ServiceScheduler::processServiceWork boost::asio::io_service::run boost::asio::detail::task_io_service::run boost::asio::detail::task_io_service::do_one boost::asio::detail::dev_poll_reactor::run The busy-wait loop continues until we stop the receiver. Also, as mentioned, the issue is always reproducible if the size of the message more than 65536 (2^16) bytes and sender and receiver are running on 2 different Solaris hosts. If both sender and receiver are running on same Solaris host then the issue is always reproducible with size 131067 (2^17). Can someone throw some light on why the ioservice thread here is continuously trying to read from the receiver though it has successfully sent the message and receiver is not actually writing anything on the socket. Please let me know if anyone came across this problem or suggest any solution. Thanks Ranadheer -- View this message in context: http://boost.2283326.n4.nabble.com/Problem-with-asych-write-when-sending-mo… Sent from the Boost - Users mailing list archive at Nabble.com.

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How to terminate a specific thread among other threads
by Master 15 Apr '12

15 Apr '12

Hello all . i have been trying to selectively dispose a thread among some other threads , but so far i wasnt successful in finding a way to do it . suppose i have a simple function which identifies any threads which gets into it and if a specific one is located ,it is disposed . simply sth like this : #include <boost/signal.hpp> #include <iostream> #include <boost/thread.hpp> using namespace std; boost::thread threadarray[3]; int t(int x) { boost::id id(); switch(boost::this_thread::get_id()) { case threadarray[0].get_id(): cout<<"thread 1"; break; case threadarray[1].get_id(): * DISPOSE THIS THREAD or CHANGE OWNERSHITP, OR GET ANOTHER JOB TO IT , OR CHECK IF IT WAS SUCCESSFUL OR NOT* break; case threadarray[3].get_id(): cout<<"thread 3"; break; default: cout<<"default"; } return 0; } int main() { boost::thread t1(t,5), t2(t,6),t3(t,7); threadarray[0] = t1.move(); threadarray[1] = t2.move(); threadarray[2] = t3.move(); for(int i = 0; i <3;i++) { threadarray[i].join(); } system("pause"); } i cant either use a switch statement to identify which thread im dealing with at the moment , nor can i find any means to keep track of my threads , and manage them in situations like this ( i already tried vector(boost::thread> my vect; and tries to use std::for_each(vect.begin(),vect.end(),somefunction_accepting boost::thread) , this doesnt work !! ) any idea how i can achieve sth similar? Thanks in advance

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[Boost State Chart] Where to include, where to declare?
by Philipp Bender 15 Apr '12

15 Apr '12

Hi all, today I face some major problems with the state charts. Mostly this comes from incorrect forward declarations and so on. I use this scheme for e.g. decaring a state which has orthogonal substates. I hope my pseudocode is readable. ############# Outer.h ############## struct Inner1 struct Inner2 struct Outer < Context, InnerDefaults< Inner1, Inner2> > { // implementation } #include Inner1 // this is the really important part #include Inner2 ############## Inner(1|2).h ######## struct Inner(1|2) < Outer > { // implementation } ################################# Doing so, I am able to use Outer in the Inner files without including something and so on -- but as soon as I start to create a file called "Inner1.cpp" and only write '#include "Inner.h" ' the problems start and the compiler complains that "Outer" ist not declared (what is true I guess). What works is to include the "Outermost" which is the state machine in my case ... but this would mean that every state knows about my state machine. Also, in my approach the cpp files need to be recompiled completely every time I think also if only the header of a completely unrelated state changes (because each cpp includes the complete state chain). So ... what's the suggested way to go? I'd like to have as little dependencies as possible, so not "all_forward_declarations.h" or some such. I had it like that, and it was a big mess. And I like the states to be separated ... Best regards, Philipp

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Set fusion::vector value with boost::shared_ptr
by Stefan Troeger 15 Apr '12

15 Apr '12

Hello alltogether, I've posted this already in Stackoverflow a week ago with no answer up to now, so I thougth I try it here again. I want to set a value in a fusion::vector at a specific location. This works normaly very well with fusion::at_c(seq) = value, as at_c returns a reference to the object at this position. However, this is not garanted, the documentation only states about the return type: "In most cases, this is a reference". I've encounterd a case where it is not a reference, when the objects are of type boost::shared_ptr<anytype>. Therefore I cant set the values as I'm only overriding a temporary. Minimal example: struct Object1{}; struct Object2{}; typedef fusion::vector<boost::shared_ptr<Object1>, boost::shared_ptr<Object2> > seq_type; seq_type seq; boost::shared_ptr<Object1> value(new Object1()); fusion::at_c<0>(seq) = value; assert(fusion::at_c<0>(seq) ); //assert will be executed because the default constructed empty pointer was not overridden with a valid one BOOST_MPL_ASSERT(( boost::is_reference< result_of::at_c<seq_type, 0>::type > )) //compilation fails because the returned type is not a reference What is a valid alternative of setting the pointers in an fusion sequence? Any help would be appreciated! Thanks, Stefan

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