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Re: Blank data file

by kvale (Monsignor)
on Jul 09, 2002 at 21:15 UTC ( #180611=note: print w/ replies, xml ) Need Help??

in reply to Blank data file

I have seen this problem before, due to multiple processes trying to read and write files simulataneously. Here is a more cautious style of locking using flock that hasn't let me down yet (probably adapted from the Cookbook, I can't remember):

# reading open NEWSRC, "< $newsgroup_file" or die "Could not open newsgroup file $newsgroup_file\n"; unless (flock NEWSRC, LOCK_SH | LOCK_NB) { print "Contention: cannot get a shared lock the file, blocking ($!) +...\n"; unless (flock NEWSRC, LOCK_SH) { die "ERROR: cannot get a shared file lock on $newsgroup_file: $! +\n"; } } print "Initial newsrc read lock granted\n"; my @news_lines = <NEWSRC>; close NEWSRC; # writing open NEWSRC, "+< $newsgroup_file" or die "Could not open newsgroup file $newsgroup_file\n"; unless (flock NEWSRC, LOCK_EX | LOCK_NB) { print "$group ($$): Contention: cannot get an exclusive lock the fi +le,\n blocking ($!) ...\n"; unless (flock NEWSRC, LOCK_EX) { die "$group ($$): ERROR: cannot get an exclusive file lock on $n +ewsgroup_file: ($!)\n"; } } print "$group ($$): Write lock granted\n"; print NEWSRC @news_lines or die "Disk full\n"; close NEWSRC;

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