[sensors] Introduce Generic Sensor API interfaces

device/sensors/platform_sensor_provider.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/sensors/platform_sensor_provider.h"
+
+namespace device {
+
+// static
+PlatformSensorProvider* PlatformSensorProvider::Create(
+    uint64_t shared_buffer_size) {
+  // TODO(shalamov): Add platform-specific PlatformSensorProvider
+  // implementations here.
+  return nullptr;
+}
+
+PlatformSensorProvider::PlatformSensorProvider(uint64_t shared_buffer_size)
+    : shared_buffer_size_(shared_buffer_size) {}
+
+PlatformSensorProvider::~PlatformSensorProvider() = default;
+
+scoped_refptr<PlatformSensor> PlatformSensorProvider::CreateSensor(
+    SensorType type,
+    uint64_t size,
+    uint64_t offset) {
+  DCHECK(CalledOnValidThread());
+
+  if (!CreateSharedBufferIfNeeded())
+    return nullptr;
+
+  mojo::ScopedSharedBufferMapping mapping =
+      shared_buffer_handle_->MapAtOffset(size, offset);
+  if (!mapping)
+    return nullptr;
+
+  // Create new platform sensor instance.
+  auto new_sensor = CreateSensor(type, std::move(mapping), size);

[dcheng, 2016/07/01 09:17:24]

Note the current guidance is not to use auto to hold smart pointer types. Also,
please #include <utility> for std::move (here and elsewhere)

[shalamov, 2016/07/01 14:22:47]

Done.

+  if (!new_sensor)
+    return nullptr;
+
+  const auto& add_result =
+      sensor_map_.insert(std::make_pair(type, new_sensor.get()));
+  DCHECK(add_result.second);
+
+  return add_result.first->second;

[dcheng, 2016/07/01 09:17:24]

return new_sensor is slightly more efficient here.

[shalamov, 2016/07/01 14:22:47]

Done.

+}
+
+scoped_refptr<PlatformSensor> PlatformSensorProvider::GetSensor(
+    SensorType type) {
+  DCHECK(CalledOnValidThread());
+
+  auto it = sensor_map_.find(type);
+  if (it != sensor_map_.end())
+    return it->second;
+  return nullptr;
+}
+
+bool PlatformSensorProvider::CreateSharedBufferIfNeeded() {
+  DCHECK(CalledOnValidThread());
+  if (shared_buffer_handle_.is_valid())
+    return true;
+
+  return mojo::CreateSharedBuffer(nullptr, shared_buffer_size_,
+                                  &shared_buffer_handle_) == MOJO_RESULT_OK;
+}
+
+void PlatformSensorProvider::RemoveSensor(SensorType type) {
+  DCHECK(CalledOnValidThread());
+  auto it = sensor_map_.find(type);
+  if (it != sensor_map_.end())
+    sensor_map_.erase(it);
+
+  if (sensor_map_.empty() && shared_buffer_handle_->is_valid())
+    shared_buffer_handle_.reset();
+}
+
+mojo::ScopedSharedBufferHandle
+PlatformSensorProvider::GetClonedSharedBufferHandle() {
+  DCHECK(CalledOnValidThread());
+  CreateSharedBufferIfNeeded();
+  return shared_buffer_handle_->Clone();
+}
+
+}  // namespace device