Copy open_locked() from tinderbox.pl and use it to optionally acquire a

lock file upon startup.  If this fails, tbmaster will simply terminate.

tools/tools/tinderbox/tbmaster.1

@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 21, 2004
+.Dd August 18, 2004
 .Dt TBMASTER 1
 .Os
 .Sh NAME
@@ -45,7 +45,7 @@ runs, generates log summaries, and mails out failure reports.
 .Pp
 The following options are recognized:
 .Bl -tag -width 12n
-.It Fl c Ar CONFIG , Fl -config Ns = Ns Ar CONFIG
+.It Fl c Ar NAME , Fl -config Ns = Ns Ar NAME
 The name of the configuration to use.
 If specified multiple times, all listed configurations will be run in
 sequence.
@@ -56,6 +56,11 @@ Dumps the configuration and exits without running the tinderbox.
 The directory where configuration files are located.
 The default is
 .Pa $HOME/etc .
+.It Fl l Ar FILE
+The name of a file to lock upon startup.
+If the lock is already held by another process,
+.Nm
+will terminate immediately rather than block.
 .El
 .Ss Configuration
 The

tools/tools/tinderbox/tbmaster.pl

@@ -42,6 +42,8 @@ my $COPYRIGHT	= "Copyright (c) 2003 Dag-Erling Sm
 my @configs;			# Names of requested configations
 my $dump;			# Dump configuration and exit
 my $etcdir;			# Configuration directory
+my $lockfile;			# Lock file name
+my $lock;			# Lock file descriptor
 
 my %INITIAL_CONFIG = (
     'BRANCHES'	=> [ 'CURRENT' ],
@@ -348,6 +350,46 @@ sub tinderbox($$$) {
     rename("$logfile.brief.$$", "$logfile.brief");
 }
 
+###
+### Open and lock a file reliably
+###
+sub open_locked($;$$) {
+    my $fn = shift;		# File name
+    my $flags = shift;		# Open flags
+    my $mode = shift;		# File mode
+
+    local *FILE;		# File handle
+    my (@sb1, @sb2);		# File status
+
+    for (;; close(FILE)) {
+	sysopen(FILE, $fn, $flags || O_RDONLY, $mode || 0640)
+	    or last;
+	if (!(@sb1 = stat(FILE))) {
+	    # Huh? shouldn't happen
+	    warning("$fn: stat(): $!");
+	    last;
+	}
+	if (!flock(FILE, LOCK_EX|LOCK_NB)) {
+	    # A failure here means the file can't be locked, or
+	    # something really weird happened, so just give up.
+	    warning("$fn: flock(): $!");
+	    last;
+	}
+	if (!(@sb2 = stat($fn))) {
+	    # File was pulled from under our feet, though it may
+	    # reappear in the next pass
+	    next;
+	}
+	if ($sb1[0] != $sb2[0] || $sb1[1] != $sb2[1]) {
+	    # File changed under our feet, try again
+	    next;
+	}
+	return *FILE{IO};
+    }
+    close(FILE);
+    return undef;
+}
+
 ###
 ### Print a usage message and exit
 ###
@@ -363,8 +405,9 @@ Options:
   -d, --dump                    Dump the processed configuration
 
 Parameters:
-  -c, --config=FILE             Configuration name
+  -c, --config=NAME             Configuration name
   -e, --etcdir=DIR              Configuration directory
+  -l, --lockfile=FILE           Lock file name
 
 Report bugs to <des\@freebsd.org>.
 ");
@@ -448,6 +491,7 @@ MAIN:{
 	"c|config=s"	        => \@configs,
 	"d|dump"		=> \$dump,
 	"e|etcdir=s"		=> \$etcdir,
+	"l|lockfile=s"		=> \$lockfile,
 	) or usage();
     if (@ARGV) {
 	usage();
@@ -475,6 +519,17 @@ MAIN:{
 	$configs[$n] = $1;
     }
 
+    # Acquire lock
+    if (defined($lockfile)) {
+	if ($lockfile !~ m/^([\w\/\.-]+)$/) {
+	    die("invalid lockfile\n");
+	}
+	$lockfile = $1;
+	$lock = open_locked($lockfile, O_CREAT, 0600)
+	    or die("unable to acquire lock on $lockfile");
+	# Lock will be released upon termination.
+    }
+
     # Run all specified or implied configurations
     foreach my $config (@configs) {
 	tbmaster($config);