I think that's why there's an open issue :) On Wed, Oct 21, 2015 at 3:29 PM, Seth <[email protected]> wrote:
> Is there a reason Julia doesn't use jl_array_del_end as a means to allow > users to shrink the allocation for an array (either within sizehint! or as > a separate function)? > > On Wednesday, October 21, 2015 at 12:32:04 PM UTC-7, Jacob Quinn wrote: >> >> I believe it stays allocated until the object is removed. There's an old >> issue about providing a way to "shrink" the underlying storage: >> https://github.com/JuliaLang/julia/issues/2879 >> >> -Jacob >> >> On Wed, Oct 21, 2015 at 1:26 PM, Seth <[email protected]> wrote: >> >>> Thanks, Jacob and Stefan. What happens if you overestimate? Is the >>> allocated-but-not-used memory eventually freed, or is it tied up until the >>> object gets removed? >>> >>> On Wednesday, October 21, 2015 at 12:18:28 PM UTC-7, Stefan Karpinski >>> wrote: >>>> >>>> If you expect that you're going to have to push a lot of values onto a >>>> vector, you can avoid the cost of incremental reallocation by doing it once >>>> up front. >>>> >>>> On Wednesday, October 21, 2015, Jacob Quinn <[email protected]> >>>> wrote: >>>> >>>>> The way I came to understand was to just take a peak at the [source >>>>> code]( >>>>> https://github.com/JuliaLang/julia/blob/ae154d076a6ae75bfdb9a0a377a6a5f9b0e1096f/src/array.c#L670 >>>>> <https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2FJuliaLang%2Fjulia%2Fblob%2Fae154d076a6ae75bfdb9a0a377a6a5f9b0e1096f%2Fsrc%2Farray.c%23L670&sa=D&sntz=1&usg=AFQjCNHQ3e_imUCFF2rvxf4NzFs3DTZxJQ>); >>>>> I find it pretty legible. The basic idea is that the underlying "storage" >>>>> of a Julia Array{T,N} can actually be (and often is) different than the >>>>> size(A) in Julia. sizehint! modifies that underlying storage without >>>>> changing the size(A) in Julia. >>>>> >>>>> -Jacob >>>>> >>>>> On Wed, Oct 21, 2015 at 12:46 PM, Seth <[email protected]> wrote: >>>>> >>>>>> I know it's good to use sizehint! with an estimate of the sizes of >>>>>> (variable-length) containers such as vectors, but I have a couple of >>>>>> questions I'm hoping someone could answer: >>>>>> >>>>>> 1) what are the benefits of using sizehint!? (How does it work, and >>>>>> under what circumstances is it beneficial?) >>>>>> 2) what are the implications (positive/negative, if any) of >>>>>> overestimating the size of a container? >>>>>> >>>>>> Thanks. >>>>>> >>>>> >>>>> >>
