persistent monitor eg1 {
listener l;
listener lt;
action onload {
initializeState();
initiateListeners();
ControlEvent c;
on all ControlEvent():c { handleControl(c); }
}
action initiateListeners;
Data d;
l:=on all Data():d { process(d); } // Process is moderately expensive
lt:=on all wait(0.1) { emit Average(state); }
}
action onBeginRecovery() {
l.quit(); // Discard all recovered Data events.
lt.quit(); // Stop sending intermittent updates.
// Do not flood receivers.
// Note that the ControlEvent listener is still present.
// The code throttles only Data events. If the
// ControlEvent listener is not present, this monitor
// would have no listeners and would terminate
// after this action.
}
action onConcludeRecovery() {
initiateListeners(); // Go back to normal.
}
}