Does newByteArray clear?
I'm looking to play around with an array-based structure with sub-linear worst-case bounds. Array is pretty awkward in that context because creating a new one takes O(n) time to initialize it. Is that all true of newByteArray, or can I get one with arbitrary garbage in it for cheap?
David Feuer wrote:
I'm looking to play around with an array-based structure with sub-linear worst-case bounds. Array is pretty awkward in that context because creating a new one takes O(n) time to initialize it. Is that all true of newByteArray, or can I get one with arbitrary garbage in it for cheap?
newByteArray# does not actively clear memory. However, for large arrays, I think the memory is likely to be freshly allocated from the OS, and the OS will have cleared it for security reasons. Cheers, Bertram
Thanks! I'm still going to feel free to pretend I get arrays for free :-).
I'm guessing I'll get some reused ones from the Haskell allocator, and the
OS is of course free to do clearing work on another core. It'd be awfully
nice to have a way to get "incrementally-cleared" arrays of pointers, but
that would require a new heap object type, which would be a lot to ask for.
On Wed, Aug 26, 2020, 8:56 PM Bertram Felgenhauer via Glasgow-haskell-users
David Feuer wrote:
I'm looking to play around with an array-based structure with sub-linear worst-case bounds. Array is pretty awkward in that context because creating a new one takes O(n) time to initialize it. Is that all true of newByteArray, or can I get one with arbitrary garbage in it for cheap?
newByteArray# does not actively clear memory.
However, for large arrays, I think the memory is likely to be freshly allocated from the OS, and the OS will have cleared it for security reasons.
Cheers,
Bertram _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
On 27/08/2020 02.56, Bertram Felgenhauer via Glasgow-haskell-users wrote:
David Feuer wrote:
I'm looking to play around with an array-based structure with sub-linear worst-case bounds. Array is pretty awkward in that context because creating a new one takes O(n) time to initialize it. Is that all true of newByteArray, or can I get one with arbitrary garbage in it for cheap?
newByteArray# does not actively clear memory.
However, for large arrays, I think the memory is likely to be freshly allocated from the OS, and the OS will have cleared it for security reasons.
Not sure how common it is in practice, but it's worth noting that OS'es should be able to clear freed memory as a background process, so that they don't have to do it on demand at the precie point of allocation. Of course this depends on memory churn, etc. etc., so it's not exactly guaranteed even if the OS supports it. Regards,
participants (3)
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Bardur Arantsson -
Bertram Felgenhauer -
David Feuer