Yes, we should probably have a manual chapter on memory management.
On Tue, Jul 8, 2014 at 12:46 PM, Abraham Egnor <abe.eg...@gmail.com> wrote: > Mostly I was looking for documentation on performance characteristics, > although I'd settle for anything at all :) The Julia home page and manual > have zero mention of memory management that I could find, except for a FAQ > entry about unbinding large values in the REPL. I inferred GC but the > runtime could also have been using refcounting, region inference, or > something more exotic. > > > On Tue, Jul 8, 2014 at 1:26 PM, Patrick O'Leary <patrick.ole...@gmail.com> > wrote: > >> You may also find this pull request interesting: >> https://github.com/JuliaLang/julia/pull/5227 >> >> >> On Tuesday, July 8, 2014 11:31:12 AM UTC-5, Abraham Egnor wrote: >>> >>> Are there any plans to document the Julia GC (i.e. your comment implies >>> that it's a stop-the-world GC) and/or add performance tuning knobs? >>> >>> >>> On Tue, Jul 8, 2014 at 12:17 PM, Stefan Karpinski <ste...@karpinski.org> >>> wrote: >>> >>>> Writing `A = nothing` in Julia will not cause the memory used by A to >>>> be freed immediately. That happens in reference counted systems, which many >>>> dynamic languages traditionally have been, but which Julia is not. Instead, >>>> the memory for A will be freed the next time a garbage collection occurs. >>>> This consists of the language runtime stopping everything it's doing, >>>> tracing through the graph of all objects in memory, marking the ones it can >>>> still reach, and freeing all the rest. So if doing `A = nothing` causes >>>> there to be no more reachable references to the object that A used to point >>>> at, then that object will be freed when the next garbage collection occurs. >>>> Normally, garbage collection occurs automatically when the system tries to >>>> allocate something and doesn't have enough memory to do so: it runs the >>>> garbage collector and then tries again. You can, however, call gc() to >>>> force garbage collection to occur now. This is generally not necessary or >>>> recommended. >>>> >>>> >>>> On Mon, Jul 7, 2014 at 11:04 PM, Ivar Nesje <iva...@gmail.com> wrote: >>>> >>>>> In julia we don't say you shouldn't do something that could give >>>>> better performance (if you really want it). The thing is that Julia uses >>>>> automatic garbage collection because it is a pain to do manually, and then >>>>> you have to live with the semantics of a garbage collector. >>>>> >>>>> If your program is not really constrained by memory in the second >>>>> part, I would guess that it is unlikely that it would matter to your >>>>> program when the arrays are released. Freeing memory in julia (and other >>>>> GC >>>>> based languages), is about ensuring that no references remains to the >>>>> allocated object. >>>>> >>>>> If it is a global variable, you can assign `nothing`, and if it is a >>>>> global constant, you can change the type, so you must reassign it to a >>>>> smaller array with the same dimensionality and type and ensure that you >>>>> don't have local variables that references the same array. >>>>> >>>>> If it is a local variable, I'm not sure there is other options than to >>>>> arrange the function boundaries, so that the large array goes out of scope >>>>> when it is not needed any more. >>>>> >>>>> kl. 22:56:35 UTC+2 mandag 7. juli 2014 skrev Pablo Zubieta følgende: >>>>> >>>>>> Let's say I have some large matrices I need to do some calculations >>>>>> and I use them in order to get some results that I will use in a second >>>>>> part of a computation where I not longer need the initial matrices. >>>>>> Suppose >>>>>> also that I preallocate those matrices. >>>>>> >>>>>> Would it be ok to bind the names of those matrices to nothing (or >>>>>> something similar) from the moment I won't be using them anymore, or >>>>>> should >>>>>> I leave the deallocation work to the GC? >>>>>> >>>>> >>>> >>> >
