Mobile: discovery keeps running after connect, holding the WiFi MulticastLock for the whole session #359

Found on: real device — Samsung SM-A166U1 (Galaxy A16 5G), Android 14 / API 34. App v3.3.0 (6537a3d). On-device session 2026-09-12.

What a user does

Taps Scan for devices, then taps a device to connect.

What happens

The scan keeps running. The button still reads "Stop scanning" after a successful connect, and the WifiManager.MulticastLock taken for discovery stays held for the rest of the session.

Measured with adb shell dumpsys wifi:

# during the scan
Multicast Locks held:
    Multicaster{daqifi-discovery uid=10265}
mMulticastEnabled 2 / mMulticastDisabled 1

# after tapping the device and connecting successfully
Multicast Locks held:
    Multicaster{daqifi-discovery uid=10265}
mMulticastEnabled 3 / mMulticastDisabled 2

Starting a stream does stop it (the scan button disappears), but stopping the stream starts discovery again while still connected, and the lock is retaken.

The lock itself is correctly balanced — an explicit Stop scanning releases it and the counters settle even (verified: Multicast Locks held: empty, 2/2). So this is not a leak. It is discovery running when there is nothing left to discover.

Why it matters

MulticastLock exists to stop Android power-save-filtering incoming broadcast/multicast — which is the whole point of MulticastDiscoveryScope, and why the manifest carries CHANGE_WIFI_MULTICAST_STATE:

Required to hold a WifiManager MulticastLock — without it Android power-save-filters incoming UDP broadcast and discovery finds nothing.

Holding it continuously keeps that filtering off for the entire connected session, on a battery-powered device, alongside the WifiLock{daqifi:streaming type=4} (FULL_HIGH_PERF) the streaming service already holds. The broadcast traffic also keeps going out for a device the user has already chosen.

What should happen

A successful connect ends the discovery sweep and releases the lock, the same way starting a stream already does. Re-scanning stays available — the user can tap Scan again — and after a stream stops, discovery should not restart on its own while a device is still connected.

Severity: low

Nothing is broken or unreachable and no resource leaks. It is wasted radio and battery on a phone, and a "Stop scanning" button offering to stop something the user has no reason to think is still running.

Reproducing

adb shell dumpsys wifi | grep -A3 "Multicast Locks held"
adb shell dumpsys wifi | grep -E "mMulticastEnabled|mMulticastDisabled"

Run before scanning, during the scan, and again after connecting.