s4u::Host::on_onoff_cb(host_onoff);
s4u::Exec::on_start_cb(add_active_exec);
s4u::Exec::on_completion_cb(remove_active_exec);
s4u::Host::on_onoff_cb(host_onoff);
s4u::Exec::on_start_cb(add_active_exec);
s4u::Exec::on_completion_cb(remove_active_exec);