but this doesn't seem to always be the case.

How do you know?

-- Randal L. Schwartz, Perl hacker

I'm doing :


print "flocking now\n";
flock (FILE, 2);
print "done flocking\n";
[download]

it prints flocking now . and freezes. If I make a copy of the file, delete the original, and then copy the copy back to the original name like so:


copy foo bar
rm foo
copy bar foo
rm bar
[download]


It'll work again but only for a while then it goes back to stopping at the flock. Using ps -A I don't see any other programs running which would flock the file.
After fiddling with it for far too long, it seems to be caused by Apache timing out. This is in a cgi script. For some reason when Apache kills it off the flock isn't undone. (near as I can figure)

If apache is killing the cgi/perl process with a signal such as SIGINT, then the perl garbage collector may not be running, so it will never run close(FILE) (or equivilent) which would automatically unflock the file. What you need to do is eithier tell your program to ignore the signal or give it something to do when it recives the signal. Perl's signal handlers aren't reliable, so you should possibly go with the first method.

$SIG{INT} = 'IGNORE'; # ignore signal and keep on going, but without a
+ connection to your user
$SIG{INT} = sub { die "Received SIGINT\n" }; # normal exit with an err
+or
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I have no idea if doing that would solve your problem, but fiddling around with signal handlers in apache and on the command line might answer that question.

END
{
    flock (FILEHANDLE, 8);
    #or, more general:
    #flock (FILEHANDLE, LOCK_UN);
}
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#or, more general:
#flock (FILEHANDLE, LOCK_UN);

That isn't 'more general', that is the 'correct way'. These constants shouldn't be hard coded. Use the Fcntl module to import your systems constants.

Cheers,
KM

Actually, I think it is better to do a close FILEHANDLE; and let perl drop the flock as a part of that close. If you unlock a file and then wait to close, something else could potentially sneak in there at a "bad" time. It isn't supposed to happen but "isn't supposed" is what you are trying to preven with flocking to begin with...

--
$you = new YOU;
honk() if $you->love(perl)