Justin Tulloss wrote: > Is the trend going to be to > move away from reference counting and towards the mark-and-sweep > implementation that currently exists, or is reference counting a firmly > ingrained tradition?
It's hard to predict the future, but the general feeling I get is that many people would like to keep the current reference counting behaviour, because it has a number of nice properties: * It's cache-friendly - it doesn't periodically go rampaging through large chunks of memory like mark-and-sweep tends to do. * It tends to reclaim things very promptly. This is important in a language like Python that uses dynamic allocation extremely heavily, even for trivial things like integers. It also helps with cacheing. * It's easy to make it interoperate with external libraries that have their own ways of managing memory. You don't have to take special steps to "protect" things from the garbage collector. > Would > somebody care to give me a brief overview on how the current gc module > interacts with the interpreter The cyclic GC kicks in when memory is running low. Since the reference counting takes care of any data structures that don't contain cycles, the GC only has to deal with cycles. It goes through all currently allocated objects trying to find sets whose reference counts are all accounted for by references within the set. Such a set must constitute a cycle that is not referenced anywhere from outside. It then picks an arbitrary object from the set and decrements the reference counts of all the objects it references. This breaks the cycle, and allows the reference counting mechanism to reclaim the memory. Although the cyclic GC requires passing over large chunks of memory like mark-and-sweep, it happens far less frequently than would happen if mark-and-sweep were used for all memory management. Also, the programmer can minimise the need for it by manually breaking cycles where they are known to occur. -- Greg Ewing, Computer Science Dept, +--------------------------------------+ University of Canterbury, | Carpe post meridiem! | Christchurch, New Zealand | (I'm not a morning person.) | [EMAIL PROTECTED] +--------------------------------------+ _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
