Re: [PATCH] tee: Add --pipe-check to allow instantly detecting closed outputs

[Pádraig Brady]

On 27/11/2022 11:32, Arsen Arsenović wrote:
> Arsen Arsenović <arsen@aarsen.me> writes:
>
> > Looking at ``check_output_alive'', this logic should be fairly easy to
> > reuse.  Worst case, I'd need to refactor some of the code to handle the
> > non-pipe-check case more elegantly so that it doesn't become too
> > unreadable when also adding the logic to pick between poll and select.
>
> Got some free time again.  The more I think about how to do this, the
> more it feels like the solution involves a portable poll or poll-like
> function that gets translated to select() if need be on a given
> platform, which sounds an awful lot like Gnulib ;).  The
> ``check_output_alive'' code checks for Gnulib poll and declares it
> incompatible, but I can't quite tell what incompatibility this is.  I
> wonder if that can be fixed?

I vaguely remember on macos that POLLRDBAND needed to be set on read fds for 
select,
though didn't check all combinations since we didn't actually need
the poll() replacement.  Also select() (emulation of poll) doesn't work on
Solaris or AIX, so we needed to explicitly disable emulation there.

Perhaps we could adjust poll() emulation to be compat everywhere,
but I'm not confident.

> If not, I can make factor out the check_alive logic and have it also
> check for file descriptors with input data.  Sadly, I don't have many
> non-GNU and non-Linux systems to test for poll behavior on; just some
> (modern) Solaris and BSD VMs.

We can help test on esoteric systems,
especially if appropriate tests are in place.
Note https://www.nongnu.org/pretest/ which may be useful.

cheers,
Pádraig