Normally writes (of this size) are atomic so I doubt you need any type of locking mechanism. Looking at the XS code for Apache::LogFile, I see it does mutiple writes - for the message(s) and for the newline if the message(s) does not contain a newline:

 int
print(self, ...)
    Apache::LogFile self

    ALIAS:
    Apache::LogFile::PRINT = 1

    PREINIT:
    int i;
    STRLEN len;
    char *str;

    CODE:
    for(i=1; i<items; i++) {
        str = SvPV(ST(i),len);
        RETVAL += write(self->log_fd, str, len);
    }
    if(*(SvEND(ST(i-1)) - 1) != '\n')
        RETVAL += write(self->log_fd, "\n", 1);

    OUTPUT:
    RETVAL
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Under heavy load, what you're seeing is one process being put into a wait state before the newline is output. You don't mention it, but did your logfile also contain blank lines? It should've.

Since you have control, if you append a newline to $message in your _logger method before you print, your logs should come out fine under heavy load.

my $message = qq{$now [$pid] X-Loadbalancer: $lb_value ($status)\n} ;
print Tiscali::LoadBalancerLogFile $message ;
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