[RFC] 4950302: (fs spec) Random write produces different results on Linux vs Windows from same .class

[Brian Burkhalter]

> On Nov 19, 2019, at 4:52 PM, David Lloyd <david.lloyd at redhat.com> wrote:
> 
> Wow, that's super unfortunate.

Indeed. Not the only OS bug we’ve had to deal with.

> What if, on Linux (newer kernels only unfortunately), instead of using
> O_APPEND at open, instead use pwritev2() and pass RWF_APPEND when
> writing if the channel was opened for append?  This would eliminate
> the extra system calls.  If you pass a -1 as the offset to that call
> with that flag set, then the file's offset is updated.

This sounds like it is worth investigating. I was unaware of it. Thanks for the suggestion.

> You'd have to add a test (to class init?) to try the call; if it
> returns ENOSYS (likely for kernels before 4.6) or EINVAL (kernels
> before 4.16) then a flag could be set and the dispatcher could fall
> back to the less-optimal behavior (sort of similarly to how sendfile
> is detected).  Alternatively, the uname(2) function could be used to
> detect that kernel version is at least 4.16, but I guess that might be
> the only place where it would be done that way.
> 
> At least then there would be a chance for optimal behavior.

A chance better than nothing!

Thanks,

Brian
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.java.net/pipermail/nio-dev/attachments/20191119/93107591/attachment.html>