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] > <javascript:>> 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. >>>>> >>>> >>>> >
