printd

• Caution: system programming ahead

 use strict;
 use Sys::Syslog;
 use Fcntl ':flock';
 use lib '/home/mjd/lib';
 use MJD::Print;
 my %CONF = load_conf($CONFIG);
 my $NEXTOP = 0;

 open STDERR, ">>", '/tmp/printd.err' if $CONF{debug_printd};
 print STDERR "printd $$ running\n" if $CONF{debug_printd};
 close STDOUT;
 chdir $CONF{spooldir} 
 or die "Couldn't chdir to spool directory $CONF{spooldir}: $!; aborting";
 open D, "." or die "Couldn't open .: $!; aborting";
 flock D, LOCK_EX | LOCK_NB 
 or exit 0;
 print STDERR "Got lock.\n" if $CONF{debug_printd};
 mainloop();

• The only interesting item here is flock

• This ensures that only one printd is running at a time

• The printd might exit if there is nothing for it to do

• When print wants to print, it should also start printd

• If printd is already running, that is OK

• open D, "." is highly nonportable

• open D, "<", 0ドル would have been a better choice