IO::Reactor on a disk file?

[Lloyd Zusman]

I have been experimenting with IO::Reactor to implement a multi-file
"tail -f". It works, but the `select' call that is made within
IO::Reactor returns immediately with a ":read" indication whether there
is new data to read at the end of the file or not [this is with
`poll(-1)']. Therefore, I can get my "tail -f" logic to work, but only
at the expense of lots of useless looping.

Is there something I can do to make the `select' call block at end
of file until new data appears, or is the behavior I'm seeing intrinsic
to `select' on a Unix system? I'm using FreeBSD, if that makes any
difference.

I have already successfully implemented a multi-file "tail -f" in ruby
using a different approach, and so I'm not looking for a solution to
that particular problem. I'm just experimenting with IO::Reactor and
I'm curious about this property of `select'.

Thanks in advance for any light that any of you can shed on this.

 

[Lloyd Zusman]

Never mind ... I figured out the answer to my question. See below:

[ ... ]

Is there something I can do to make the `select' call block at end
of file until new data appears, or is the behavior I'm seeing intrinsic
to `select' on a Unix system? I'm using FreeBSD, if that makes any
difference.

The `select' manpage on my FreeBSD system says nothing about EOF, but I
looked at a Linux manpage for that function, and it states that `select'
will consider a file descriptor to be `ready' for reading even if it's
in the EOF state. That explains the behavior I'm seeing.

Sorry for the bandwidth.

 

[Yohanes Santoso]

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to `select' on a Unix system? I'm using FreeBSD, if that makes any

select() is not particularly useful in dealing with disk i/o. It
always indicates readiness for any disk i/o. AFAIK, most unix-like
OSes share this behaviour. I seem to remember that only some unix-like
OSes in 1970-1980 that do not.

YS.

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