> 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
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