August 2007 - Boost-users - lists.preview.boost.org

Statechart serialization
by mbrodeur65 04 Mar '15

04 Mar '15

Hi, I'm looking for a solution to serialize boost::statechart objects. I'm aware that this feature is on the statechart library todo list but was wondering if there are any workaround to achieve this with the latest boost release (1.34) ? thanks for your help ! mbrodeur65 -- View this message in context: http://www.nabble.com/Statechart-serialization-tf4131326.html#a11749139 Sent from the Boost - Users mailing list archive at Nabble.com.

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[asio] resolver::cancel() problem
by Matthew Edwards 14 Mar '14

14 Mar '14

In my application (and a separate test program) it seems as though the cancel() function on the resolver does not work as intended. For async resolves, the cancel functionality should abort them immediately and pass an 'operation aborted' error code to the callback handler. In my tests, I will resolve an invalid domain (this causes the resolve to take a few seconds, to demonstrate the problem), sleep for 100ms, then call cancel on the resolver object. No cancelling actually occurs, and the callback is simply triggered after a few seconds with a "No host found" error code, not the expected operation aborted. Has anyone experienced this before, or know how I might be using the resolver incorrectly?

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[multi_array] operator= requires resize - why?
by Markus Werle 04 Jun '12

04 Jun '12

Hi! IMHO the behaviour of operator= for multi_array is a little bit broken. A lot of preconditions required: template <typename ConstMultiArray> multi_array_ref& operator=(const ConstMultiArray& other) { [...] // make sure the dimensions agree assert(other.num_dimensions() == this->num_dimensions()); assert(std::equal(other.shape(),other.shape()+this->num_dimensions(), this->shape())); Besides the fact that I get mad about asserts instead of exceptions (please change this to a way users may choose) why do we have such an odd behaviour here? >From page 1, line 3 of the docs I cite: "The interface design is in line with the precedent set by the C++ Standard Library containers" - this is not true for operator=, since std::<container>::operator= works fine for me all the time _without_ any resize. Could we please change the behaviour of multi_array::operator= to take care of resize where in need to? IMHO operator= should result in a true copy ignoring previous state. Markus

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Design for boost::serialization of STL iterators.
by Carlo Wood 23 May '09

23 May '09

On Sat, Mar 11, 2006 at 11:45:36PM +0200, Peter Dimov wrote: > Carlo Wood wrote: > > > 1) WHY does boost::serialization not support serialization > > of iterators? > > It's very hard, if not impossible, in general. It is either impossible or possible. When it is possible, it can't be hard :p I think that at the moment of serialization, the actual container needs to be known. So, only concentrating on the syntax of the code that serializes an iterator, the following cannot work: ar & iter; However, the container will be known at that point (or at least, we might as well assume that). Therefore, I could imagine a syntax like: ar & foobar(container, iter); where 'foobar' is some template function (that will be part of boost::serialization in the future). Lets start with the last one (have to start somewhere). In order to deserialize the iterator (and taken into account that we already have the container) -- which makes me think that it might be better to pass a functor to operator& above. In other words, (at least for writing), use: template<class Container> struct Foobar { Foobar(Container const&, typename Container::const_iterator& iter) : M_container(container), M_iter(iter); private: Container const& M_container; Container::const_iterator& M_iter; }; and then assign to M_iter, whatever we find in M_container. > If you have access to the container to which the iterator i refers: > > a) if the container is a map, you can serialize i->first, then on > deserialization look up the key in the map using .find(); > > b) if the container is a sequence, and it has the same contents on > deserialization as it does on serialization, you can serialize the index of > the element - distance( c.begin(), i ). I don't think that it is a requirement that the whole container has to be read: either it's a map or set, in which case later insertions will not invalidate the container, or it is a vector, in which case we use an index, from which we can construct the end iterators before the whole container is reconstructed. Therefore, the following syntax can work imho: ar & FooBar(container, iter); Would you agree? There are a zillion questions and implementation details open - but I'd like to get anyones feedback about this type of interface for iterators before continuing. Current questions: What is a good name for Foobar? Am I right when I think that Foobar needs to be declared in boost::serialization? Now the hard part (for me) is that part that involves the internals of the boost library. At the moment one tries to serialize an iterator, it is possible (though not necessarily) that the object that the iterator points to is already serialized. In the case that we are dealing with an associative container (map or set etc), we don't want to store the contents of the object (or key part, in the case of a map) again: I'd like to just store that once, and store a reference in the archive at the other place. How can I make the library store an object only the first time and the store a reference the second time? This would be for an object of arbitrary type thus. I think that it is only feasible to do this when it's actually the same object (same memory address), which is the case; but while storing the object element of the container, the address of it isn't stored as well, is it? Is there a way to make: std::set<SomeData> s; [...] ar << s; Store the address of s (&s) along with the contents of s? And would that then automatically cause the library to not store that same object again when I do: std::set<SomeData>::iterator iter = s.find(...); [...] ar << *iter; Because then, &*iter would again be the same memory address as what was stored before. -- Carlo Wood <carlo(a)alinoe.com>

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[BGL] citing the Boost Graph Library
by Alejandro Marcos Aragón 06 May '09

06 May '09

Can anyone point me how to cite the Boost Graph Library in a paper? Is there any information in the boost website? Thank you all, Alejandro Aragón

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Boost Graph Library and Boehm Garbage Collector
by FBSL 08 Sep '08

08 Sep '08

Hello I am having trouble to garbage-collect adjacency_list<>. I have instanciated it with correctly garbage-collected vectors and lists (I have copied vecS and listS definitions, and added Boehm GC's default allocator so that they are garbage-collected). In my application I need to dynamically allocate many graphs, but it does not work, there is a (big) memory leak. Unfortunately, there is no template argument in adjacency_list<> to specify Boehm GC's allocator. Does anyone have a hint ? Snippet code "main.cpp" follows, compiled with Boost Graph Library 1.32, Boehm GC 6.4 and G++ 3.3.5, with command line : $ g++ -o main main.cpp -lgc -lgccpp -- #include <boost/graph/adjacency_list.hpp> #include <gc/gc_allocator.h> #include <gc/gc_cpp.h> #include <iostream> #include <vector> #include <list> using namespace std; using namespace boost; namespace boost { struct collected_vecS {}; struct collected_listS {}; template <class ValueType> struct container_gen<collected_vecS, ValueType> { typedef vector<ValueType,gc_allocator<ValueType> > type; }; template <class ValueType> struct container_gen<collected_listS, ValueType> { typedef list<ValueType,gc_allocator<ValueType> > type; }; template <> struct parallel_edge_traits<collected_vecS> { typedef allow_parallel_edge_tag type; }; template <> struct parallel_edge_traits<collected_listS> { typedef allow_parallel_edge_tag type; }; namespace detail { template <> struct is_random_access<collected_vecS> { enum { value = true }; typedef true_type type; }; } } typedef adjacency_list<collected_vecS, collected_vecS, directedS, no_property, no_property, no_property, collected_listS> graph; int main() { // leaks... while(true){ graph * g=new (UseGC) graph; for(unsigned int i=0; i<100; ++i){ add_vertex(*g); } for(unsigned int i=0; i<100; ++i){ for(unsigned int j=0; j<100; ++j){ add_edge(i,j,*g); } } } }

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[statechart] history transitions make state-local-storage "un-cool"
by Mick Hollins 26 Jun '08

26 Jun '08

Apologies if this has been discussed before, but I couldn't find any mention of it: I am currently using the history facility of boost::fsm. I've discovered that when I re-enter a state, X, via a history transition I don't actually re-enter the same instance of X that I was in before, but instead enter a newly constructed instance of X. I just checked the UML spec regarding history transitions and it says that "Any necessary entry actions are performed", so given that boost::fsm uses constructors to represent entry actions I guess a new instance of X has to be constructed to ensure UML compliance. My actual concern is the effect this has on the "coolness" of state-local-storage (see http://boost-sandbox.sourceforge.net/libs/statechart/doc/faq.html#Whats_so_…) It seems to me that state-local-storage, which I agree is generally cool, is particularly un-cool (and bug-inducing) in the presence of history transitions. I'm not sure what a good alternative is, but just thought I'd raise the discussion. cheers, mick PS: does the history facility display the same semantics in boost::statechart? I plan to move to statechart real soon now ...

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[foreach][range] How would BOOST_REVERSE_FOREACH be implemented?
by Pete Bartlett 05 Mar '08

05 Mar '08

Boost.Foreach is such a great piece of kit that once you start using it you just can't stop. Indeed I like working directly with values rather than iterators so much that is feels normal for me to write something like BOOST_FOREACH( value_type x , make_iterator_range( rbegin( seq ) , rend( seq ) ) whenever I wish to reverse iterate over a sequence. My co-workers are not big fans of typing though, so they want a REVERSE_FOREACH. At first naïve glance it looks easy to implement in terms of the original FOREACH: template<typename C> inline iterator_range</* something */> make_reverse_iterator_range(C& c) { return make_iterator_range( rbegin(c) , rend(c) ); } #define REVERSE_FOREACH( x , container ) BOOST_FOREACH( x , make_reverse_iterator_range( container ) ) This works fine when container is an lvalue. But then co-workers, used to the wonders of the original FOREACH, inevitably start to use the new macro with rvalues and get a crash due to dangling references (- the iterator_range's members point to departed quantities.....) and if you could somehow work around that, there is the issue hidden inside the "/* something */" that you have to cope with fact that MSVC has no proper const rvalue detection. Finally the #define MACRO(x,y) ANOTHER_MACRO( f(x) , g(y) ) style is not recommended because they are brittle in the face of x and/or y themselves being macros. ... but all these issues are exactly the ones that BOOST_FOREACH itself solves! Thus surely it is technically possible to write a REVERSE_FOREACH that works with rvalues as well as lvalues, e.g. by essentially copying and pasting the FOREACH implementation and replacing "begin" and "end" by "rbegin" and "rend" in the vital places. However one feels there may be a better way... has anyone had a go at creating a "fully-functional" REVERSE_FOREACH and could offer me any advice? If indeed the task is fairly intricate and requires re-use of foreach internals, would the library author consider including something in the library itself? Many thanks for reading, Pete Bartlett

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Threads, FunctionPtr and stepping through code
by Jaime Rios 19 Sep '07

19 Sep '07

Hi, I'm working on a project that uses the Boost thread library. The code is pretty simple and creates one thread to a function. To test out the code I created, I create a console app and tested the code on 2 platforms: Mac OS X for Intel and Mac OS X for PowerPC. The code worked fine in the console app so I incorporated the code into my main project, which is a dylib. The code worked fine on the Intel Mac, but when I debugged the dylib on the PowerPC Mac, I get a EXC_BAD_ACCESS error. After spending many hours trying to find out what the cause of the problem is, the only thing I could derive was that the address that Boost was using to access my function was wrong. Before the error, I have the following address to my function: (gdb) print f $1 = (void (*)(void)) 0x33658e4 <MyWorkerThread()> When I get the EXC_BAD_ACCESS error, the debugger stops at the following line: On line 95 of file function_template.hpp struct BOOST_FUNCTION_VOID_FUNCTION_INVOKER { static BOOST_FUNCTION_VOID_RETURN_TYPE invoke(any_pointer function_ptr BOOST_FUNCTION_COMMA BOOST_FUNCTION_PARMS) { HERE--> FunctionPtr f = reinterpret_cast<FunctionPtr>(function_ptr.func_ptr); BOOST_FUNCTION_RETURN(f(BOOST_FUNCTION_ARGS)); } }; The address at this point is the following: (gdb) print f $2 = (void (*)(void)) 0xf0798dd0 I went over the code over and over again but I cannot figure out what is causing the original function address to be changed. Now for the question! How can I debug this better? The problem that I am finding is that my debugger jumps to different parts of the project, but I cannot pinpoint the actual code that is causing this problem. Any suggestions? Thanks in advance! -Jaime

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[boost::serialization] Serializing Dynamically Loaded Libraries - "Unregistered Void Cast"
by Jeshua Bratman 06 Sep '07

06 Sep '07

I already sent a message on this topic a few weeks ago, however, my problem has a changed a bit so I decided to post a new message. I've been trying to get Boost serialization working for dynamically loaded shared libraries. Here's my basic structure simplified: 1. base.hpp - includes an abstract base class called base 2. derived.hpp - includes a derived class from base. includes base.hpp. 3. derived.cpp - includes code for derived class and for dynamically loading it 4. main.cpp - includes base.hpp but NOT derived.hpp. dynamically loads instantiates a base * which points to a derived object from derived.so Now in main I want to be able to serialize my pointer to the loaded derived class: base *obj = create_func(); //obj now points to a derived object obj->test(); //when test is run it correctly outputs the message from derived.cpp const base* const to_serialize = obj; std::ofstream ofs("filename"); boost::archive::text_oarchive oa(ofs); try { oa << (to_serialize); } catch(exception &e) { cout << "Exception: " << e.what() << "\n"; } It compiles fine and I got past the "unregisterd class" problem, but now when I try to serialize the pointer an exception is caught: "Unregistered void cast" This appears to be a problem with registering the derived pointer type from the base type when dynamically loaded from a shared library. However, I do register the derived-base relationship as suggested in the documentation. The serialize method in derived.hpp is as follows: template<class Archive> void serialize(Archive & ar, const unsigned int version) { ar.template register_type(static_cast<derived *>(NULL)); //ar & boost::serialization::base_object<base>(*this); ar & data; boost::serialization::void_cast_register( static_cast<derived *>(NULL), static_cast<base *>(NULL) ); } If anyone knows the cause of this and/or a solution I would be very appreciative. I've been working at this for a long time now and I'm almost ready to write my own simple serialization for my specific purpose. Thank you for your help, Jeshua Bratman -- View this message in context: http://www.nabble.com/-boost%3A%3Aserialization--Serializing-Dynamically-Lo… Sent from the Boost - Users mailing list archive at Nabble.com.

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