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;
-Mark
