C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Library proposal: STL with custom pointer objects          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Samee Zahur Guest Posted: Mon May 16, 2005 5:19 pm    Post subject: Library proposal: STL with custom pointer objects I'd like to know everyone's opinion about adding (yet) another template parameter to the STL container classes - one which will determine the kind of pointer objects the classes will use for handling contained objects. Something like this will change the vector class from template< class T,class A=allocator class vector; to this: template< class T,class A=allocator class vector Why? Whenever I go for writing an allocator class of my own, I feel like I should have something to do about the memory pool getting fragmented. A defrag attempt, however, will make all existing pointers invalid, and there will be no way for me to change the value of each and every pointer pointing to a certain place. That can be made possible if I could somehow instruct STL to use my own pointer objects to handle all the data they contain. And not just that, things like copy-on-write would be much simpler to code if it was implemented. With the different kinds of pointer objects now emerging out of libraries like boost, this can largely increase the choice of users of STL. But the question is, would we *all* like something like this? Or is it already there or something? Samee --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top P.J. Plauger Guest Posted: Mon May 16, 2005 6:09 pm    Post subject: Re: Library proposal: STL with custom pointer objects "Samee Zahur" <samee.zahur (AT) gmail (DOT) com> wrote Quote: I'd like to know everyone's opinion about adding (yet) another template parameter to the STL container classes - one which will determine the kind of pointer objects the classes will use for handling contained objects. Something like this will change the vector class from template< class T,class A=allocator class vector; to this: template< class T,class A=allocator class vector Why? Whenever I go for writing an allocator class of my own, I feel like I should have something to do about the memory pool getting fragmented. A defrag attempt, however, will make all existing pointers invalid, and there will be no way for me to change the value of each and every pointer pointing to a certain place. That can be made possible if I could somehow instruct STL to use my own pointer objects to handle all the data they contain. And not just that, things like copy-on-write would be much simpler to code if it was implemented. With the different kinds of pointer objects now emerging out of libraries like boost, this can largely increase the choice of users of STL. But the question is, would we *all* like something like this? Or is it already there or something? No and yes. The C++ Standard encourages, but does not require, a library implementation to accommodate allocators with funny pointer types. (In other words, for the type T the pointer type is not necessarily T*.) The Dinkumware implementation is the only one I know of that actually does so -- each of our STL containers uses the supplied allocator template to allocate, construct, and destroy pointers as needed. So what you want is already there, kinda. P.J. Plauger Dinkumware, Ltd. http://www.dinkumware.com --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Krzysztof ¯elechowski Guest Posted: Tue May 17, 2005 11:30 pm    Post subject: Re: Library proposal: STL with custom pointer objects Uzytkownik "Samee Zahur" <samee.zahur (AT) gmail (DOT) com> napisal w wiadomosci news:1115893047.429623.201420 (AT) g49g2000cwa (DOT) googlegroups.com... Quote: Whenever I go for writing an allocator class of my own, I feel like I should have something to do about the memory pool getting fragmented. A defrag attempt, however, will make all existing pointers Heap fragmentation is only an issue when you cannot fit a large objects between two small ones. How can you get this effect with standard template data structures? I thought all your objects should be of equal size. Chris --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Larry Evans Guest Posted: Tue May 17, 2005 11:32 pm    Post subject: Re: Library proposal: STL with custom pointer objects On 05/16/2005 12:19 PM, Samee Zahur wrote: Quote: I'd like to know everyone's opinion about adding (yet) another template parameter to the STL container classes - one which will determine the kind of pointer objects the classes will use for handling contained objects. Something like this will change the vector class from template< class T,class A=allocator class vector; to this: template< class T,class A=allocator class vector Why? Whenever I go for writing an allocator class of my own, I feel like I should have something to do about the memory pool getting fragmented. A defrag attempt, however, will make all existing pointers invalid, and there will be no way for me to change the value of each and every pointer pointing to a certain place. That can be made possible if I could somehow instruct STL to use my own pointer objects to handle all the data they contain. AFAICT, it would also enable refcounted pointers to be garbage collected even when cycles are present. The existing boost shared_ptr has a proposed garbage collector for collecting cycles in the pointer graph: http://cvs.sourceforge.net/viewcvs.py/boost/boost/libs/smart_ptr/src/sp_collector.cpp?rev=1.4&view=auto however, IIUC, it cannot collect cycles when the smart pointers are in something like an stl collection, e.g. vector<shared_ptr, because the "root" pointer of the vector (i.e. that returned by begin() ) is not registered as a pointer by the function: boost::sp_scalar_constructor_hook WARNING: The above reasoning is just a guess, but I remember discussing this somewhere either here or on the boost new group. Hopefully Peter Dimov will give a more definite answer. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Samee Zahur Guest Posted: Thu May 19, 2005 3:13 am    Post subject: Re: Library proposal: STL with custom pointer objects Krzysztof ¯elechowski wrote: Quote: Heap fragmentation is only an issue when you cannot fit a large objects between two small ones. How can you get this effect with standard template data structures? I thought all your objects should be of equal size. Chris Well, if everyone is using the same heap, different map<int> and map<bigclass> can easily keep on allocating/deallocating elements to create fragmentation ... and many many other classes totally unrelated to STL! P.J. Plauger wrote Quote: The Dinkumware implementation is the only one I know of that actually does so -- each of our STL containers uses the supplied allocator template to allocate, construct, and destroy pointers as needed. So what you want is already there, kinda. So the only thing that's not there is the 'manditory' part ... so if I write a code here, it might not be acceptable everywhere ... hmm ... but I think I can live with that! Thanks! Sanee --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Larry Evans Guest Posted: Fri May 20, 2005 10:01 pm    Post subject: Re: Library proposal: STL with custom pointer objects On 05/16/2005 01:09 PM, P.J. Plauger wrote: [snip] Quote: No and yes. The C++ Standard encourages, but does not require, a library implementation to accommodate allocators with funny pointer types. (In other words, for the type T the pointer type is not necessarily T*.) The Dinkumware implementation is the only one I know of that actually does so -- each of our STL containers uses the supplied allocator template to allocate, construct, and destroy pointers as needed. I've needed a specialized smart pointer for use in stl containers to allow precise garbage collection. A prototype created several years ago is at: http://boost-sandbox.sourceforge.net/vault/index.php?&direction=0&order=&directory=cppljevans/policy_ptr I'm currently working on a newer version of the precise gc which I hope to upload soon to: http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/boost/policy_ptr/ Does the Dinkumware implementation allow something that shown in the vault file referenced above? IOW, does it allow something like: allocator_type::root_pointer where root_pointer is a pointer as described in the above file as: typedef prox_children::prox_indirect_typed<Value> root_pointer /**@variable root_pointer * @brief * The proxy from which all elements of * the container may be reached. */ ; For the existing stl containers, instead of: prox_children::prox_indirect_typed<Value> this would simply be: Value* -regards Larry --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ] Back to top Larry Evans Guest Posted: Mon Jun 27, 2005 6:31 pm    Post subject: Re: Library proposal: STL with custom pointer objects On 05/20/2005 05:01 PM, Larry Evans wrote: Quote: On 05/16/2005 01:09 PM, P.J. Plauger wrote: [snip] No and yes. The C++ Standard encourages, but does not require, a library implementation to accommodate allocators with funny pointer types. (In other words, for the type T the pointer type is not necessarily T*.) The Dinkumware implementation is the only one I know of that actually does so -- each of our STL containers [snip] I've needed a specialized smart pointer for use in stl containers to allow precise garbage collection. A prototype created several years ago is at: http://boost-sandbox.sourceforge.net/vault/index.php?&direction=0&order=&directory=cppljevans/policy_ptr I'm currently working on a newer version of the precise gc which I hope to upload soon to: http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/boost/policy_ptr/ The newer version is currently at: http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/boost/fields_visitor/container_intern/#dirlist It's use in an stl-like container is shown in vector.hpp in the same directory. The specialization for allowing traversal of the elements is in: prox_indirect_registrar_heirarchy.hpp Actual use in precise garbage collection is demonstrated by: http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/libs/policy_ptr/test/std_ptr_binary_node_test.cpp when the Jamfile.v2 in that director is used (or when macro USE_CONTAINER_INTERN is defined). Adapting Dinkumware's stl library to use this type of pointer, i.e. prox_indirect, wouldn't pose any problems, would it? adapting --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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