C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  stl string class performance          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Thomas Guest Posted: Fri Sep 26, 2003 4:14 pm    Post subject: stl string class performance Does anyone know if the stl string class implements some sort of pooling or chunking of memory for performance optimization? I know that the Lucent SCL has this built in, but not sure if the same is true of STL. The platform is Solaris 2.8. Thanks, Thomas Back to top Ron Natalie Guest Posted: Fri Sep 26, 2003 4:41 pm    Post subject: Re: stl string class performance "Thomas" <tdineen (AT) att (DOT) com> wrote Quote: Does anyone know if the stl string class implements some sort of pooling or chunking of memory for performance optimization? I know that the Lucent SCL has this built in, but not sure if the same is true of STL. The platform is Solaris 2.8. You haven't indicated what implementation you are talking about. #include <string> #include <iostream> using namespace std; int main() { string s; while(true) { s += " "; cout << s.size() << " " << s.capacity() << "n"; } } For the G++ version I tried, size and capacity track each other up to 116 charaacters, then the capacity starts jumping 227, 355, 483, 611, 739... Back to top Thomas Guest Posted: Fri Sep 26, 2003 7:32 pm    Post subject: Re: stl string class performance Ron, Thanks for the feedback. What I was looking for was more along the lines of a separate pool object, i.e. memory manager, that would handle the memory allocation for all the objects. Rather than having to ask the o.s for additional memory, it (string, list, etc) would get it from the pool object. If the pool object didn't have enough, it would then have to reallocate. Once the string, list, etc were done with the memory, it would get returned to the pool object. My reason for asking is that if SCL has this implementation in place and the vendor supplying the STL does not, then it is very likely that I can expect considerable performance degradation when migrating to STL. The application I support uses strings and lists extensively and would benefit significantly from that optimization. I am using the Solaris version that comes with 6.2 on Solaris 8. Thanks again, Thomas "Ron Natalie" <ron (AT) sensor (DOT) com> wrote Quote: "Thomas" <tdineen (AT) att (DOT) com> wrote Does anyone know if the stl string class implements some sort of pooling or chunking of memory for performance optimization? I know that the Lucent SCL has this built in, but not sure if the same is true of STL. The platform is Solaris 2.8. You haven't indicated what implementation you are talking about. #include #include using namespace std; int main() { string s; while(true) { s += " "; cout << s.size() << " " << s.capacity() << "n"; } } For the G++ version I tried, size and capacity track each other up to 116 charaacters, then the capacity starts jumping 227, 355, 483, 611, 739... Back to top Kevin Goodsell Guest Posted: Fri Sep 26, 2003 8:07 pm    Post subject: Re: stl string class performance Thomas wrote: Quote: Ron, Thanks for the feedback. snip Please don't top-post. Read section 5 of the FAQ for posting guidelines. http://www.parashift.com/c++-faq-lite/ -Kevin -- My email address is valid, but changes periodically. To contact me please use the address from a recent posting. Back to top John Tsiombikas (Nuclear Guest Posted: Fri Sep 26, 2003 9:17 pm    Post subject: Re: stl string class performance Thomas wrote: Quote: Ron, Thanks for the feedback. What I was looking for was more along the lines of a separate pool object, i.e. memory manager, that would handle the memory allocation for all the objects. Rather than having to ask the o.s for additional memory, it (string, list, etc) would get it from the pool object. If the pool object didn't have enough, it would then have to reallocate. Once the string, list, etc were done with the memory, it would get returned to the pool object. I would expect most implementations to be quite optimized, making OS system calls for every allocation would be quite stupid in most systems. Quote: My reason for asking is that if SCL has this implementation in place and the vendor supplying the STL does not, then it is very likely that I can expect considerable performance degradation when migrating to STL. The application I support uses strings and lists extensively and would benefit significantly from that optimization. There isn't such thing as "the STL vendor", The C++ Standard Library is a specification, there are many different implementations, for instance every compiler usually has its own Standard Library implementation. Quote: I am using the Solaris version that comes with 6.2 on Solaris 8. Thanks again, Thomas then go to a solaris-specific newsgroup or a newsgroup dedicated to the compiler you use on solaris and ask them about their implementation of the Standard Library. -- Nuclear / the Lab -- Back to top jeffc Guest Posted: Fri Sep 26, 2003 9:40 pm    Post subject: Re: stl string class performance "John Tsiombikas (Nuclear / the Lab)" <nuclear (AT) siggraph (DOT) org> wrote in message news:1064611010.658265 (AT) athprx02 (DOT) .. Quote: My reason for asking is that if SCL has this implementation in place and the vendor supplying the STL does not, then it is very likely that I can expect considerable performance degradation when migrating to STL. The application I support uses strings and lists extensively and would benefit significantly from that optimization. There isn't such thing as "the STL vendor", The C++ Standard Library is a specification, there are many different implementations, for instance every compiler usually has its own Standard Library implementation. He didn't say "the STL vendor". He said "the vendor supplying the STL". This implies the vendor supplying the STL implementation (see the first half of the sentence.) Back to top Mike Wahler Guest Posted: Fri Sep 26, 2003 11:42 pm    Post subject: Re: stl string class performance "Thomas" <tdineen (AT) erols (DOT) com> wrote Quote: Ron, Thanks for the feedback. What I was looking for was more along the lines of a separate pool object, i.e. memory manager, that would handle the memory allocation for all the objects. Rather than having to ask the o.s for additional memory, it (string, list, etc) would get it from the pool object. If the pool object didn't have enough, it would then have to reallocate. Once the string, list, etc were done with the memory, it would get returned to the pool object. See the 'allocator' template argument for std::string. Also don't forget member functions 'reserve()' and 'resize()'. Quote: My reason for asking is that if SCL has this implementation in place and the vendor supplying the STL does not, then it is very likely that I can expect considerable performance degradation when migrating to STL. You can provide your own allocator via a template argument. Quote: The application I support uses strings and lists extensively and would benefit significantly from that optimization. All the containers can have allocator template arguments. -Mike Back to top Jerry Coffin Guest Posted: Sat Sep 27, 2003 4:20 am    Post subject: Re: stl string class performance In article <bl248t$nj9$1 (AT) bob (DOT) news.rcn.net>, [email]tdineen (AT) erols (DOT) com[/email] says... Quote: Ron, Thanks for the feedback. What I was looking for was more along the lines of a separate pool object, i.e. memory manager, that would handle the memory allocation for all the objects. Rather than having to ask the o.s for additional memory, it (string, list, etc) would get it from the pool object. If the pool object didn't have enough, it would then have to reallocate. Once the string, list, etc were done with the memory, it would get returned to the pool object. There's nothing in the standard to mandate behavior like this, but it's a fairly accurate description of how things _usually_ work. The containers in the standard library allow the user to specify an allocator object that will be used to allocate memory for the collection. The default allocator will use new and delete to allocate and free memory. Since it's not observable behavior (in the way "observable" is meant by the standard) there's no requirement that new and delete allocate large chunks of memory from the OS, and sub-allocate out of those. In fact, I know of one version of one compiler that _did_ use OS calls every time you allocated or freed memory -- that's a rare (and long-since obsolete) exception though. Simple market pressure prevents it from becoming common; nearly everybody has at least a few competitors, and speeding up the default new and delete will give a competitor a substantial improvement in both benchmark scores AND in real speed, so most try to make it at least pretty good (though if it becomes an issue, there are after-market memory managers that might be worth looking into). -- Later, Jerry. The universe is a figment of its own imagination. 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