LAN broadcast triggers background processing

[Matthew Exon]

I'm not currently considering porting my app to Ubuntu, but it seems to be a class of use cases not yet covered, so... I run a website which sells electronic tickets encoded as a QR code. The app is for event organisers to scan the QR codes and ensure each is only scanned once. (The app is free/proprietary, the ticketing system costs money.) There might be multiple phones scanning tickets so they need to synchronise their scanning history. The app pull-synchronises with the server over the WAN using a one-minute timer. It also push-synchronises triggered by push notifications. But this is slow and depends on an internet connection. For faster or offline syncing, phones also broadcast to each over the LAN. iOS limitations dramatically impede performance of this process. Users frequently switch off their phones or switch to another app. Ideally as soon as the user turns on their phone it would show up-to-date totals and history. In fact this has to wait for a slow synchronisation process. So my requirement is that the phone stays awake listening to the broadcast port and stores new records in its SQLite database, updates any totals, and gets ready for when the app wakes up. The one-minute timer should also run regardless of whether the app is focused. Note that battery life here is normally not an issue, doors are open for only a few hours and it's easy to keep a USB battery on hand.