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[Interprocess] Opposite of find_or_construct()
by Aaron_Wright＠selinc.com 19 Apr '12

19 Apr '12

I feel like I'm missing something simple. I have multiple processes that are going to use an object in shared memory. The find_or_construct() method lets these processes get a pointer to the object without worrying about startup order. What about the opposite? When a process is done with the object in shared memory it can't destroy it because the other processes may be using it. Is there a destroy_or_not() method that would only destroy the object when everyone is done with it? Normally I would solve this with a smart pointer like shared_ptr, but I think I'm miss understanding smart_ptr and I can't get it to work right. It seems like the shared_ptr is created in shared memory and needs to be explicitly destroyed, which would bring me back to the original problem, of who actually gets to destroy it. Should I be looking at intrusive_ptr? --- Aaron Wright

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Calling dijkstra on a filtered graph with bundled properties?
by Berit Dangaard Brouer 18 Apr '12

18 Apr '12

Hi there, First of all thank you for the boost graph library - I really enjoy working with it. However I have become challenged in calling Dijkstra on a filtered graph with bundled properties: My graph structure "mcf_graph" looks like this: #ifndef MCF_GRAPH_HPP #define MCF_GRAPH_HPP #include <boost/config.hpp> #include <boost/graph/adjacency_list.hpp> #include <iostream> using namespace boost; using namespace std; struct Port { Port(int index=-1, int type=0, int port_code=0, string UN="NN", string name="NN", int service_id=-1 ): m_index(index), m_type(type), m_port_code( port_code), UNLOCODE(UN), m_name(name), m_service_id(service_id) {} int m_index; int m_type;//0 port, 1 port call int m_port_code; string UNLOCODE; string m_name; int m_service_id; }; struct Edge { Edge( int id=0, int type=0, double weight=0.0, double dual_cost=0.0, double util=0.0, double cap=0.0, double r_cap=0.0 ) : m_idx(id), m_type(type), m_weight(weight) , m_dual_cost(dual_cost), m_utilization(util), m_capacity(cap), m_res_cap(r_cap) {} unsigned int m_idx; int m_type; double m_weight; double m_dual_cost; double m_utilization; double m_capacity; double m_res_cap; //residual capacity }; template <typename res_cap_map> struct positive_res_cap { positive_res_cap() { } positive_res_cap( res_cap_map cap) : res_cap(cap) { } bool operator()(const Edge& e) const { return 0 < e.m_res_cap; } res_cap_map res_cap; }; //Graph typedef adjacency_list< vecS , vecS , bidirectionalS, Port, Edge> mcf_graph; private: mcf_graph& g; }; #endif I am filtering an mcf_graph like this: //filter positive residual capacity graph positive_res_cap<res_cap_map> filter(get(&Edge::m_res_cap, m_mcf->graph())); filtered_graph<mcf_graph, positive_res_cap<res_cap_map> > fg(m_mcf->graph(), filter); and then calling Dijkstra like this: vertex_descriptor o_vd; std::vector<vertex_descriptor> p ( num_vertices ( fg ) ); std::vector<double> d ( num_vertices ( fg ) ); dijkstra_shortest_paths ( fg, o_vd, predecessor_map ( &p[0] ).distance_map ( &d[0] ).weight_map ( get ( &Edge::m_weight,fg ) ).vertex_index_map ( get ( vertex_index,fg ) ) ); and I get the following compilation error: /usr/include/boost/graph/filtered_graph.hpp:75:63: error: no match for call to '(const positive_res_cap<boost::bundle_property_map<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, Port, Edge>, boost::detail::edge_desc_impl<boost::bidirectional_tag, unsigned int>, Edge, double> >) (const boost::detail::edge_desc_impl<boost::bidirectional_tag, unsigned int>&)' /home/berit/svn/MCF/src/IPH/include/mcf_graph.h:54:8: note: candidate is: /home/berit/svn/MCF/src/IPH/include/mcf_graph.h:57:7: note: bool positive_res_cap<res_cap_map>::operator()(const Edge&) const [with res_cap_map = boost::bundle_property_map<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, Port, Edge>, boost::detail::edge_desc_impl<boost::bidirectional_tag, unsigned int>, Edge, double>] /home/berit/svn/MCF/src/IPH/include/mcf_graph.h:57:7: note: no known conversion for argument 1 from 'const boost::detail::edge_desc_impl<boost::bidirectional_tag, unsigned int>' to 'const Edge&' The above call to Dijkstra works on a non-filtered graph. Can anyone help me out in both understanding why it does not work for the predicate (Is it because the iterators are different???) and how to solve my problem? Thanks in advance ! Berit -- Best Regards, Berit Dangaard Brouer (formerly Løfstedt) PhD. Student DTU Management Engineering, Operations Research Technical University of Denmark Department of Management Engineering Produktionstorvet, Bygning 426 2800 Kgs. Lyngby blof(a)dtu.dk <mailto:blof@man.dtu.dk> www.or.man.dtu.dk <http://www.or.man.dtu.dk>

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Timeout on read/write using Boost.Asio
by boost 18 Apr '12

18 Apr '12

Hi everyone I'm using boost asio to implement a tcp client in my project, and it is my first time of using asio. I need timeout when read/write on the socket and I found the solution of using async io plus a timer, if timeout, cancel the async io operation. My question is: the "cancel" call acutely cancel all the pending async operation, but only one of them is timeout. For example, there is a pending async read and a pending async write operation, only read is timeout, I do not want cancel write any way. Any suggestion of the solution? Or I' m wrong? Thanks

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shared_ptr and container iterators
by Johannes Totz 18 Apr '12

18 Apr '12

Hi all, just started playing with boost::shared_ptr. How do I get a const iterator pointing to a shared_ptr pointing to a const object? See code below, I'd like to prevent a MyItem being changed through const iterators. struct MyItem { int value; }; struct MyContainer { typedef std::set<boost::shared_ptr<MyItem> > MySet; MySet set; }; int main(int argc, char* argv[]) { MyContainer mc; boost::shared_ptr<MyItem> p(new MyItem); p->value = 5; mc.set.insert(p); MyContainer::MySet::const_iterator i = mc.set.begin(); // cannot mutate shared_ptr pointed to by iterator: ok //(*i).reset(new MyItem); // cannot change ptr but can change value: ok (*i)->value = 6; MyContainer::MySet::iterator j = mc.set.begin(); (*j).reset(new MyItem); // how to do this? // should not change ptr nor MyItem std::set<boost::shared_ptr<const MyItem> >::const_iterator k = mc.set.begin(); return 0; }

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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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