in reply to singleton lock not reliable
Many thanks to all who took the time to respond. Key seems to be using a writable lock file. The following version has been running over a month with no dups so I'll call it good.
# only one of us my $LOCKFN = "/tmp/x.mylock"; open my $LF, '>', $LOCKFN or die "Can not create $LOCKFN: $!"; flock ($LF, LOCK_EX | LOCK_NB) or exit;
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