[26776] in Perl-Users-Digest
Perl-Users Digest, Issue: 8843 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Mon Jan 9 14:05:17 2006
Date: Mon, 9 Jan 2006 11:05:07 -0800 (PST)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Mon, 9 Jan 2006 Volume: 10 Number: 8843
Today's topics:
Re: IO::Pipe and loss of data xhoster@gmail.com
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: 09 Jan 2006 17:55:51 GMT
From: xhoster@gmail.com
Subject: Re: IO::Pipe and loss of data
Message-Id: <20060109125551.943$NM@newsreader.com>
"Ina Scherf" <ina.scherf@sap.com> wrote:
> >
> >> sub logProcessing{
> >> my $line = '';
> >> my ($msg, $server);
> >> eval {
> >> local $SIG{ALRM} = sub { die "lesedauer" };
> >> alarm(1);
> >> $line = <$pipe_log>;
> >> alarm(0);
> >> };
> >
> > I don't understand the point of this time out. If the timeout occurs,
> > you never complain about it or even detect it. You merely start
> > another call of the same thing that just timed out. If all you do upon
> > a timeout is restart the same thing, why bother timing out?
> This seems to be obsolete because I cut away code. Normally the father
> process shall do three things parallel in its routine. One of them has to
> do with user input to another script and sending data. So I wanted to
> reduce wating time at this point (although I believe this pipe is _never_
> empty for over one second).
If it is never empty for more than a second, then it should be safe to
remove the timeout :) At least for debugging purposes.
Or at least do a
die "$@: $line:" if $@;
(or a warn, or a logging command)
after the end of the eval block.
>
> > Anyway, if the alarm goes off after the next line is read from
> > $pipe_log, but before the "alarm(0)" gets executed, then you die out of
> > the eval{} and
> > the line you just read from $pipe_log gets ignored. That could account
> > for
> > your missing data!
> But should not be at least half a line in $line then?
Maybe, maybe not. I think that $line = <$pipe_log>; is executed first as a
read from pipe_log into some anonymous storage, then as an assignment from
that storage into $line. If the interuption happens after (or during)
the read but before the assingment, then $line will show no hint of the
missing data, (other than being empty, which event is silently ignored in
the code as you originally posted it.)
> I changed my log to
> have the old line and the new line. No half lines so far. Either there is
> the whole line or nothing in it. And it is very easy to check if the line
> is not complete as the last thing to be transfered is a dumped object and
> this gives an error on every missing character at the end.
>
> >> return if ($line !~ /::/);
> > Wouldn't it be better to die upon malformed data?
> Yes - you're completely right :)
Have you seen the error after making this change? (This is where you
silently ignore empty lines, which, in conjuction with your alarm time-out,
might be the cause of the missing data).
....
>
> I give out either the last line that was send sucessfully and the new
> line after the missing one. Both seem to be just normal - nothing is
> missing.
This definitely makes me thinkg the problem is with the time-out, and not
with the pipe itself.
Xho
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Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 8843
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