tree 8fe6a7aedd8705501347c95a69adcd4d513c9930
parent 6748e62ef25c8072e1f0b37be634dc08fc983bd8
author Lorenzo Colitti <lorenzo@google.com> 1617287765 +0900
committer Lorenzo Colitti <lorenzo@google.com> 1617630733 +0900

Fix a race condition in upstream selection.

Current upstream selection code suffers from a race where if the
CONNECTIVITY_ACTION broadcast for a given network switch is
received and processed before the NetworkCallbacks for that
network switch, upstream selection just re-selects the same
upstream it had before. The incorrect upstream persists until
another CONNECTIVITY_ACTION is received.

Fix this by defining a new EVENT_DEFAULT_SWITCHED message code
communicated from UpstreamNetworkMonitor to Tethering, and send
that whenever the default network switches.

The message is sent in onLinkPropertiesChanged, because the
tethering code stores all information about networks in an
UpstreamNetworkState structure that contains Network,
LinkProperties and NetworkCapabilities. When a network switch
occurs, onLinkPropertiesChanged always follows onAvailable and
onCapabilitiesChanged, and thus marks the first point in time
when all the information is available.

This CL tries not to change existing codepaths too much, but
it does move the update of mDefaultInternetNetwork from
onCapabilitiesChanged to onLinkPropertiesChanged. This should
not be a problem because the only thing that reads
mDefaultInternetNetwork is getCurrentPreferredUpstream, which,
in the case of a default network switch, will be run by the
onLinkPropertiesChanged which will immediately follow.

Bug: 173068192
Test: changes to existing unit tests show bug is fixed
Change-Id: Ic9196bc92892811b25bda463ffd839ee5c19d294