# subroutine name: syswritedata
# Writes in all the data to $datafile.
# Owerwrites file, if already exists
# If error occurs, makes CGI process exit with error
# Returns: nothing
#
# Global variables used:
#	$no_flock - disable flock or not
sub syswritedata {
	my($datafile, $content) = @_;
	# If OS (like Win95) desn't support flock, we have to
	# go unreliable and slow way and create "lock" file
	GetFileLock("$datafile.lock");
	my $existed = -e $datafile;
	use Fcntl qw( O_RDWR O_WRONLY O_CREAT O_TRUNC );
	local *DATA;
	if (sysopen(DATA, $datafile, &O_WRONLY | &O_CREAT)) {
		# Exclusive locking
		flock(DATA, 2) unless ($no_flock);
		truncate(DATA, 0) or die "Can't truncate $datafile. Reason: $!";
		print DATA $content;
		# unlock file
		flock(DATA, 8) unless ($no_flock);
		close(DATA);
		chmod(0666, $datafile) unless ($existed);
		ReleaseFileLock("$datafile.lock");
	} else {
		ReleaseFileLock("$datafile.lock");
		die("Error in subroutine syswritedata: Can't open $datafile. Reason: $!");
	}
}