On Thursday, September 7, 2017 at 9:49:33 AM UTC-7, Volker Braun wrote: > > First question: The GAP garbage collector might delete objects, or it > might move existing objects around in memory (it is a compacting garbage > collector). If your code contains C pointers to GAP objects, bad things > will happen after that. Not every libGAP_* function can invoke the garbage > collector, and for those that do it will not always run a collection cycle. > But there are no documented guarantees that any particular libGAP_* > function does not run garbage collection, or may be changed to run garbage > collection in the future. >
Ouch. Gap indeed uses a compactifying garbage collector. But are you saying it will adjust the *stack*, for which the garbage collector doesn't know the exact layout? Then, if I have an integer on the stack that happens to coincide in bit pattern with a pointer to a moved Gap object, this integer could get changed. That's a low probability event, but not the kind of thing that mathematical software can take chances with. Are you sure it does that? (it seems it would have to ...) A conservative GC like Boehm can get away with interpreting values as pointers if in doubt: at the worst it prevents an unreachable object to not be GCd because it seems it's reachable, but it won't turn results of valid code into nonsense. A compacting GC has to know for sure which values are pointers and which are not. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
