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Avoiding flush on-change sensors at subscription

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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
This commit is contained in:
Peng Xu 2015-10-26 15:14:43 -07:00
parent 2ac7405bda
commit 20483c4937
1 changed files with 9 additions and 4 deletions
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13
services/sensorservice/SensorService.cpp
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@ -912,10 +912,15 @@ status_t SensorService::enable(const sp<SensorEventConnection>& connection,
status_t err = sensor->batch(connection.get(), handle, 0, samplingPeriodNs, status_t err = sensor->batch(connection.get(), handle, 0, samplingPeriodNs,
maxBatchReportLatencyNs); maxBatchReportLatencyNs);
// Call flush() before calling activate() on the sensor. Wait for a first flush complete // Call flush() before calling activate() on the sensor. Wait for a first
// event before sending events on this connection. Ignore one-shot sensors which don't // flush complete event before sending events on this connection. Ignore
// support flush(). Also if this sensor isn't already active, don't call flush(). // one-shot sensors which don't support flush(). Ignore on-change sensors
if (err == NO_ERROR && sensor->getSensor().getReportingMode() != AREPORTING_MODE_ONE_SHOT && // 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) { rec->getNumConnections() > 1) {
connection->setFirstFlushPending(handle, true); connection->setFirstFlushPending(handle, true);
status_t err_flush = sensor->flush(connection.get(), handle); status_t err_flush = sensor->flush(connection.get(), handle);