Hi guys, If you're working on any piece of code that needs to be relatively high performance and you're using Qt data structure, there's a really important caveat to be aware of:
http://harmattan-dev.nokia.com/docs/library/html/guide/html/Developer_Library_Best_practices_for_application_development_Performance_management_Coding_for_performance.html#Avoiding_deep_copies_in_Qt And I quote: "To get the best out of implicit sharing, use the at() function rather than the [] operator for read-only access of a (non-const) vector or list. Since Qt's containers cannot tell whether [] appears on the left side of an assignement or not, it assumes the worst and forces a deep copy to occur. The at() function is not allowed on the left side of an assignment and thus it does not create a deep copy. A similar issue occurs when you iterate over a container with Qt's STL-style iterators. Whenever begin() or end() is called on a non-const container, Qt forces a deep copy to occur if the data is shared. To prevent this, use const_iterator, constBegin(), and constEnd() whenever possible." This is a VERY important point if you're working in almost any thread in Mixxx, so keep an eye out for this sort of thing (in both existing code and whatever you're working on or reviewing). Stay vigilant! Thanks, Albert -- Albert Santoni Developer, Mixxx http://www.mixxx.org http://www.oscillicious.com ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Get Mixxx, the #1 Free MP3 DJ Mixing software Today http://mixxx.org Mixxx-devel mailing list Mixxx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mixxx-devel
