Work on threading in opencog is on-hold because it seems like a difficult problem. However, I was reading something recently, which makes me think that perhaps a change of mindset could convert this difficult problem into an "easy" one, by changing certain core assumptions.
I was reading about Clojure http://wiki.jvmlangsummit.com/pdf/27_Hickey_clojure.pdf which is a LISP implementation on top of the JVM. One of the things that Hickey talks about is multi-threading, and how "easy" it is, because of a core design assumption he made: expressions would be immutable. This rang a bell: the hypergraphs in opencog are currently "immutable", in the sense that, once I create something like SomeLink SomeAtom "asdf" OtherAtom "pqrs" I can not change the string values "asf" or "pqrs", I cannot add more atoms to the link, I cannot remove the existing atoms from the link, I cannot delete these atoms from the link, unless I also delete the link first. So at least one key concept from clojure already exists in opencog: immutablity. The key element that seems to be missing from opencog is garbage collection. That is, although the incoming set for "SomeAtom" will reveal that "SomeLink" is pointing at it, we don't know who is pointing at SomeLink. Thus, there is no safe way of deleting "SomeLink" if there is more than one "MindAgent" (forget threads -- even when single threaded, if one MindAgent is holding a pointer to SomeLink, its unsafe to delete it). If garbage collection was added, I think the multi-threading issues just might go away (I haven't pondered deeply on this, though). I'm also thinking that adding something conservative, like the Boehm garbage collector, might be pretty easy, almost trivially so, as it might not require any big tear-up of the code ... or even a small tear-up. The only interesting pieces would be to integrate it properly with the ForgettingAgent, and &etc. -- and I guess with the TLB and handles, since these act as pseudo-pointers. Anyone care to ponder this in greater detail? --linas _______________________________________________ Mailing list: https://launchpad.net/~opencog-dev Post to : [email protected] Unsubscribe : https://launchpad.net/~opencog-dev More help : https://help.launchpad.net/ListHelp
