> On May 10, 2017, at 11:52 , Joe Groff <jgr...@apple.com> wrote:
>
>
>> On May 8, 2017, at 4:47 PM, Rick Mann via swift-users
>> <swift-users@swift.org> wrote:
>>
>> I have this C library that interacts with some hardware over the network
>> that produces a ton of data. It tells me up front the maximum size the data
>> might be so I can allocate a buffer for it, then does a bunch of network
>> requests downloading that data into the buffer, then tells me when it's done
>> and what the final, smaller size is.
>>
>> Thanks to previous discussions on the list, I settled on using a [UInt8] as
>> the buffer, because it let me avoid various .withUnsafePointer{} calls (I
>> need the unsafe buffer pointer to live outside the scope of the closures).
>> Unfortunately, When I go to shrink the buffer to its final size with:
>>
>> self.dataBuffer = Array(self.dataBuffer![0 ..< finalBufferSize])
>>
>> This ends up taking over 2 minutes to complete (on an iPad Pro).
>> finalBufferSize is very large, 240 MB, but I think it's doing a very naive
>> copy.
>>
>> I've since worked around this problem, but is there any way to improve on
>> this?
>
> `self.dataBuffer!.removeSubrange(finalBufferSize ..<
> self.dataBuffer!.endIndex)` might be more efficient. However, copying an
> array of bytes definitely shouldn't be that slow, so is worth a bug report.
>
> -Joe
Here you go: https://bugs.swift.org/browse/SR-4856
Easy to reproduce in a Playground.
--
Rick Mann
rm...@latencyzero.com
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