Do not send stale event to on-change sensor
When a client requests to activate an on-change sensor, the
SensorService sends the previous sensor event to the new client if
the sensor is already active. This is necessary to ensure that the new
client receives a sensor event since it is unknown when the sensor may
generate a new sensor event.
If two clients simultaneously activate the same on-change sensor that
is currently not active, then the second client would receive a sensor
event from the previous activation which may be from a significant
time ago, leading to an inconsistent state between the clients.
This patch checks that the last sensor event it would send to the
second client is from the current sensor activation in order to
prevent sending any stale sensor events.
Bug: 116283108
Test: 1) Artificially added delay to generate on-change sensor event.
2) Requested on-change sensor from client 1
3) Requested on-change sensor from client 2
4) Verified that client 2 did not receive a stale sensor event
5) Verified that client 1 and client 2 both received the same
up-to-date sensor event
Test: Verified that above test case fails at step 4 without this patch
Change-Id: I49587e3da7177882a1e8e67347bbb64acfe38200
diff --git a/services/sensorservice/SensorService.cpp b/services/sensorservice/SensorService.cpp
index 1b9b945..85450f8 100644
--- a/services/sensorservice/SensorService.cpp
+++ b/services/sensorservice/SensorService.cpp
@@ -1290,6 +1290,15 @@
ALOGD_IF(DEBUG_CONNECTIONS, "... and it was the last connection");
mActiveSensors.removeItemsAt(i, 1);
mActiveVirtualSensors.erase(handle);
+
+ // If this is the last connection, then mark the RecentEventLogger as stale. This is
+ // critical for on-change events since the previous event is sent to a client if the
+ // sensor is already active. If two clients request the sensor at the same time, one
+ // of the clients would receive a stale event.
+ auto logger = mRecentEvent.find(handle);
+ if (logger != mRecentEvent.end()) {
+ logger->second->setLastEventStale();
+ }
delete rec;
size--;
} else {
@@ -1356,10 +1365,11 @@
auto logger = mRecentEvent.find(handle);
if (logger != mRecentEvent.end()) {
sensors_event_t event;
- // It is unlikely that this buffer is empty as the sensor is already active.
- // One possible corner case may be two applications activating an on-change
- // sensor at the same time.
- if(logger->second->populateLastEvent(&event)) {
+ // Verify that the last sensor event was generated from the current activation
+ // of the sensor. If not, it is possible for an on-change sensor to receive a
+ // sensor event that is stale if two clients re-activate the sensor
+ // simultaneously.
+ if(logger->second->populateLastEventIfCurrent(&event)) {
event.sensor = handle;
if (event.version == sizeof(sensors_event_t)) {
if (isWakeUpSensorEvent(event) && !mWakeLockAcquired) {