[Sensors] Improvements in shared buffer managing

device/generic_sensor/platform_sensor.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "device/generic_sensor/platform_sensor.h"
 
 #include <utility>
 
+#include "base/threading/thread_task_runner_handle.h"
 #include "device/generic_sensor/platform_sensor_provider.h"
 #include "device/generic_sensor/public/cpp/platform_sensor_configuration.h"
 
 namespace device {
 
 PlatformSensor::PlatformSensor(mojom::SensorType type,
                                mojo::ScopedSharedBufferMapping mapping,
                                PlatformSensorProvider* provider)
-    : shared_buffer_mapping_(std::move(mapping)),
+    : task_runner_(base::ThreadTaskRunnerHandle::Get()),
+      shared_buffer_mapping_(std::move(mapping)),
       type_(type),
       provider_(provider),
       weak_factory_(this) {}
 
 PlatformSensor::~PlatformSensor() {
   provider_->RemoveSensor(GetType());
 }
 
 mojom::SensorType PlatformSensor::GetType() const {
   return type_;
@@ skipping 45 matching lines @@
 void PlatformSensor::RemoveClient(Client* client) {
   DCHECK(client);
   clients_.RemoveObserver(client);
   auto client_entry = config_map_.find(client);
   if (client_entry != config_map_.end()) {
     config_map_.erase(client_entry);
     UpdateSensorInternal(config_map_);
   }
 }
 
+void PlatformSensor::UpdateSensorReading(const SensorReading& reading,
+                                         bool notify_clients) {
+  ReadingBuffer* buffer =
+      static_cast<ReadingBuffer*>(shared_buffer_mapping_.get());
+  auto& seqlock = buffer->seqlock.value();
+  seqlock.WriteBegin();
+  buffer->reading = reading;
+  seqlock.WriteEnd();
+
+  if (notify_clients)
+    task_runner_->PostTask(
+        FROM_HERE, base::Bind(&PlatformSensor::NotifySensorReadingChanged,
+                              weak_factory_.GetWeakPtr()));
+}
+
 void PlatformSensor::NotifySensorReadingChanged() {
   using ClientsList = decltype(clients_);
   ClientsList::Iterator it(&clients_);
   Client* client;
   while ((client = it.GetNext()) != nullptr) {
     if (!client->IsNotificationSuspended())
       client->OnSensorReadingChanged();
   }
 }
 
@@ skipping 17 matching lines @@
 
   if (!optimal_configuration) {
     StopSensor();
     return true;
   }
 
   return StartSensor(*optimal_configuration);
 }
 
 }  // namespace device