8227080: (fs) Files.newInputStream(...).skip(n) is slow

[Brian Burkhalter]

Hi Florian,

> On Jul 3, 2019, at 7:11 AM, Florian Weimer <fweimer at redhat.com> wrote:
> 
>> This patch overrides ChannelInputStream.skip(long) to use
>> SeekableByteChannel.position(long) if the ReadableByteChannel instance
>> is a SeekableByteChannel. The performance improvement on my dev
>> machine for skipping the first 2 GB of a local file is about 3.6 x
>> 10^4.
> 
> Doesn't this need a fallback in case the seek operation fails?  I think
> you can have FileChannels which are not seekable in practice, e.g. if
> the file is actually a FIFO.

Would that not violate the SeekableByteChannel specification? On the other hand, I suppose one might be able to fall back to super.skip(). If the seek however actually did skip a few bytes before failing then it would be possible to skip an incorrect number of bytes in this case.

Thanks,

Brian
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