Avoiding flush on-change sensors at subscription
Initial sensor flush at subscription is a mechanism to avoid sensors
to get stale samples before subscription happens. However, there is a
slight chance that a most recent sample will be lost during the flush
process. This is OK for continuous sensors but problematic in
on-change sensor as on-change event does not come continuously and
a lost event can cause inconsistent state in client. Flush at
subscription of on-change sensor is disabled in this CL to avoid new
important on-change event to be discarded during the initial flush
process.
Bugs: b/24647069
b/25241873
b/24804819
Change-Id: Ibda099c6b9f5fb6e200f13cf13a850b0026e9e7c
diff --git a/services/sensorservice/SensorService.cpp b/services/sensorservice/SensorService.cpp
index 40b21a9..fd72b23 100644
--- a/services/sensorservice/SensorService.cpp
+++ b/services/sensorservice/SensorService.cpp
@@ -912,10 +912,15 @@
status_t err = sensor->batch(connection.get(), handle, 0, samplingPeriodNs,
maxBatchReportLatencyNs);
- // Call flush() before calling activate() on the sensor. Wait for a first flush complete
- // event before sending events on this connection. Ignore one-shot sensors which don't
- // support flush(). Also if this sensor isn't already active, don't call flush().
- if (err == NO_ERROR && sensor->getSensor().getReportingMode() != AREPORTING_MODE_ONE_SHOT &&
+ // Call flush() before calling activate() on the sensor. Wait for a first
+ // flush complete event before sending events on this connection. Ignore
+ // one-shot sensors which don't support flush(). Ignore on-change sensors
+ // to maintain the on-change logic (any on-change events except the initial
+ // one should be trigger by a change in value). Also if this sensor isn't
+ // already active, don't call flush().
+ if (err == NO_ERROR &&
+ sensor->getSensor().getReportingMode() != AREPORTING_MODE_ONE_SHOT &&
+ sensor->getSensor().getReportingMode() != AREPORTING_MODE_ON_CHANGE &&
rec->getNumConnections() > 1) {
connection->setFirstFlushPending(handle, true);
status_t err_flush = sensor->flush(connection.get(), handle);
