Re: using lexically scoped variable as a filehandle

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Re^2: using lexically scoped variable as a filehandle by shmem (Chancellor) on Feb 21, 2007 at 14:04 UTC
Can you think of circumstances in which close will fail? I do :-) If you say `open my $fh, '>>', $file or die $!;` [download] you should also say `close $fh or die $!;` [download] when done, IMHO. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^3: using lexically scoped variable as a filehandle by BrowserUk (Patriarch) on Feb 21, 2007 at 15:24 UTC
Can you think of circumstances in which close will fail? I do :-) If you say `open my $fh, '>>', $file or die $!;` you should also say `close $fh or die $!;` when done, IMHO I'm gonna call you on this. Not because you are wrong, but because I haven't made up my about it mind yet. Let's consider both scenarios when the close fails: The open append may fail for a variety of reasons. Existance, permissions, in-use etc. Dying at this point in the proceedings may waste whatever work was done till now, but the (this) output file hasn't been touched, so recovery probably consists of correcting whatever caused the failure and re-running the program. For the close to fail, it basically come down to one reason, thought here could be several underlying causes, that some amount of written & cached, but unflushed output, could not be flushed to disk. Recovery is all together more complicated. The file has almost certainly been modified, but not in a consistant manner, so the error definitely needs to be recorded. Unless the application makes provision to record the file length prior to writing to the file, there is no possibility of automated recovery, as there is no way to determine how much was not flushed. But dying at this point achieves nothing accept to ensure that all subsequent processing is aborted, which will often compound the problem--by leaving other persistance state in a indeterminate place--rather than alleviating it. </lo> So, IMO, you almost never want to die on close failure, warn maybe, but not die. Update: I also question the likelyhood of close actually failing, but that's probably a different discussion. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l] [select]
Re^4: using lexically scoped variable as a filehandle by jhourcle (Prior) on Feb 21, 2007 at 15:40 UTC
Update: I also question the likelyhood of close actually failing, but that's probably a different discussion You've never tried writing to a full disk, or a mounted filesystem that went away mid-process then. It's not likely for most people, but it does happen. I do agree that just 'die'ing on failure is a bad thing for these sorts of situations, though.	[reply]
Re^5: using lexically scoped variable as a filehandle by BrowserUk (Patriarch) on Feb 21, 2007 at 16:33 UTC
Re^6: using lexically scoped variable as a filehandle by Tanktalus (Canon) on Feb 21, 2007 at 16:56 UTC
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Re^4: using lexically scoped variable as a filehandle by shmem (Chancellor) on Feb 21, 2007 at 17:09 UTC
So, IMO, you almost never want to die on close failure, warn maybe, but not die. If a close fails, I surely want to die, as this is an unrecoverable error. Well, I could just warn, but then? what next? sleep and wait for a signal, and later do what? If a close fails, most certainly I have data inconsistency - e.g. a corrupt file -, and that's why I have to stop further processing immediately. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply]
Re^5: using lexically scoped variable as a filehandle by BrowserUk (Patriarch) on Feb 21, 2007 at 17:53 UTC
Re^6: using lexically scoped variable as a filehandle by misterwhipple (Monk) on Feb 21, 2007 at 21:21 UTC
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Re^6: using lexically scoped variable as a filehandle by shmem (Chancellor) on Feb 21, 2007 at 18:27 UTC
Re^3: using lexically scoped variable as a filehandle by EvanK (Chaplain) on Feb 21, 2007 at 15:10 UTC
agreed, shmem, i wish more people would follow that advice. even though 99% of the time `close()` will not fail, it's always that 1% that ends up biting you in the ass :o __________ Systems development is like banging your head against a wall... It's usually very painful, but if you're persistent, you'll get through it.	[reply] [d/l]