Hi! I'm an interested spectator but understand very little :) I wonder if anyone would take a moment to explain? E.g. I can't see why reading from a data structure should ever lead to a change in the refcounts. A
On Thursday, 30 May 2013 15:56:42 UTC+1, tbc++ wrote: > > There are two things I see that reduce the viability of ref-count GCs with > Clojure: > > a) Clojure is insanely alloc heavy. Look at the source of the data > structures, merging two hash-maps (for instance) requires about 2-3 > allocations per assoc, per kv in the merged map: > > (merge map1 map2) > allocs = ~((tree-depth of map1) * (count map2) > > b) Every time you transverse a persistent structure's tree you'll need to > increment and decrement the refcounts. Consider multi-core, now the > refcounts have to be thread safe (atomic inc & dec). So if you have two > cores reading (not just writing) from the same hash-map, they'll be > fighting over the cache lines that the refcount is stored in, and that'll > kill performance. > > Timothy > > > On Thu, May 30, 2013 at 8:47 AM, Gary Trakhman > <gary.t...@gmail.com<javascript:> > > wrote: > >> At first glance, those issues seem like they could be mitigated, so I >> think I see room here for some real-time ref-counted clojure. I imagine >> it'd still have a lot of allocations so it wouldn't be that great for >> low-memory systems. >> >> >> On Thu, May 30, 2013 at 9:44 AM, Jean Niklas L'orange < >> jean...@hypirion.com <javascript:>> wrote: >> >>> >>> >>> On Thursday, May 30, 2013 2:21:36 PM UTC+2, Gary Trakhman wrote: >>>> >>>> I just thought about this recently, but does the value-oriented nature >>>> of clojure mostly void the need for a cycles-aware GC? It seems like you >>>> won't ever have cycles without identities, or pointers (java references). >>>> Maybe this would be a problem only when you need identities, ie deftype >>>> or >>>> defprotocol implementing objects. >>>> >>> >>> Sure thing, the value-oriented nature removes a lot of cycles in >>> practice. However, you may for instance have an atom which contain itself, >>> so they are not nonexistant. As such, the GC cannot be completely >>> cycle-ignorant, but perhaps it doesn't have to be efficient at finding them >>> either. >>> >>> Another place where cycles happen are in (mutually) recursive functions, >>> they may be iffy if you define many recursive anonymous functions at >>> runtime. >>> >>> -- Jean Niklas L'orange >>> >>> -- >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To post to this group, send email to clo...@googlegroups.com<javascript:> >>> Note that posts from new members are moderated - please be patient with >>> your first post. >>> To unsubscribe from this group, send email to >>> clojure+u...@googlegroups.com <javascript:> >>> For more options, visit this group at >>> http://groups.google.com/group/clojure?hl=en >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to clojure+u...@googlegroups.com <javascript:>. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >>> >>> >> >> -- >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@googlegroups.com<javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <javascript:> >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+u...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> > > > > -- > “One of the main causes of the fall of the Roman Empire was that–lacking > zero–they had no way to indicate successful termination of their C > programs.” > (Robert Firth) > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
