[ILUG] [OT] perl: file locking with flock

[John Gaughan]

> -----Original Message-----
> From: ilug-admin at linux.ie [mailto:ilug-admin at linux.ie]On Behalf Of
> Kathryn Cassidy
> Sent: 28 February 2000 16:01
> To: ilug at linux.ie
> Subject: [ILUG] [OT] perl: file locking with flock
>
>
> Agh!  I've got a wee script here which is meant to put an
> exclusive lock on
> a file, wait for a minute, then release the lock.  It goes something like
> this:
>
>     open LOCKED, '>>oqq.inc';
>
> 	$result=flock(LOCKED, LOCK_EX);

If I change this line to:
flock(LOCKED, LOCK_EX) or die "flock() failed: $!\n"

I get:
flock() failed: Invalid argument

My guess is you haven't imported the 'LOCK_*' constants flock uses, so your
attempt to flock() fails.  One other thing.  I'm not sure it this is normal
behaviour for the libc version of flock(), but if the file has been locked
already, perl's flock() appears to wait for the first lock to be released
and then locks the file, rather than returning an error.

Try this instead:

use Fcntl ':flock';  # import LOCK_* constants

open LOCKED '>>foo.txt' or die "open() failed: $!\n";
flock(LOCKED, LOCK_EX) or die "flock() failed: $!\n";
# see what time the file was locked at
print localtime(time())."\n";
sleep 60;
flock(LOCKED, LOCK_UN);
close(LOCKED);



John.