def set_max_job_count(env, count = 0):
    """
    Sets the max job count for SCons execution.
    If count == 0 then we determine the number of CPU's on the system
    and sets the maximum job count accordingly.
    """
    def get_cpu_nums():
        """
        Detects the number of CPUs on a system.
        """
        # Linux, Unix and MacOS:
        if hasattr(os, "sysconf"):
            if os.sysconf_names.has_key("SC_NPROCESSORS_ONLN"):
                # Linux & Unix:
                ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
                if isinstance(ncpus, int) and ncpus > 0:
                    return ncpus
            else: # OSX:
                return int(os.popen2("sysctl -n hw.ncpu")[1].read())
        # Windows:
        if os.environ.has_key("NUMBER_OF_PROCESSORS"):
                ncpus = int(os.environ["NUMBER_OF_PROCESSORS"]);
                if ncpus > 0:
                    return ncpus
        return 1 # Default
    job_count = get_cpu_nums() if not count else count
    print "scons: Max %d parallel jobs" % job_count
    env.SetOption("num_jobs", job_count)