From: Atom Smasher <atom@smasher.org>
To: zsh-users@sunsite.dk
Subject: Re: runaway zselect
Date: Mon, 18 May 2009 11:28:55 +1200 (NZST) [thread overview]
Message-ID: <20090517232856.6093.qmail@smasher.org> (raw)
In-Reply-To: <090517144747.ZM959@torch.brasslantern.com>
cool... thanks!
On Sun, 17 May 2009, Bart Schaefer wrote:
> On May 17, 4:43pm, Atom Smasher wrote:
> }
> } i would expect zselect to return an error and stop the while loop when
> } "w" stops producing output.
>
> That's not how the select() system call works. The descriptor is still
> open on the reading end of the pipe even though the descriptor on the
> writing end of the pipe has been closed. That means from select()'s
> point of view, the descriptor is available for reading, even though the
> only thing that can be read from it is the end-of-file condition.
>
> If this were not the case, zselect would fail as soon as the writer
> exits, even if all output from the writer had not yet been consumed.
> (Remember that there is OS-level buffering involved, so the writing end
> may be closed before the pipe is "empty".)
>
> What you need to fix this is to test the result of "read" as well.
> Either:
>
> while zselect -r 0 && read -r foo
> do
> print -r -- $foo
> done <<( w )
>
> Or equivalently:
>
> while zselect -r 0
> do
> read -r foo || break
> print -r -- $foo
> done <<( w )
>
>
--
...atom
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prev parent reply other threads:[~2009-05-17 23:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-17 4:43 Atom Smasher
2009-05-17 7:58 ` Atom Smasher
2009-05-17 21:47 ` Bart Schaefer
2009-05-17 23:28 ` Atom Smasher [this message]
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