[sensors] Introduce Generic Sensor API interfaces

device/generic_sensor/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/generic_sensor/platform_sensor_provider.h"
+
+#include <utility>
+
+#include "base/stl_util.h"
+#include "device/generic_sensor/public/interfaces/sensor_provider.mojom.h"
+
+namespace device {
+
+namespace {
+
+const uint64_t kSharedBufferSizeInBytes =
+    mojom::SensorReadBuffer::kReadBufferSize *
+    static_cast<uint64_t>(mojom::SensorType::LAST);
+
+}  // namespace
+
+PlatformSensorProvider* PlatformSensorProvider::s_instance_ = nullptr;
+
+// static
+PlatformSensorProvider* PlatformSensorProvider::GetInstance() {
+  // TODO(shalamov): Lazily initialize s_instance_ with platform-specific
+  // PlatformSensorProvider implementations here.
+  return s_instance_;

[timvolodine, 2016/08/19 16:02:30]

we usually use return base::Singleton<.... instead of having a member s_instance
in chromium

you could have a platform_sensors_provider_base.{h,cc} with shared code and then
platform_sensor_provider.h deriving from it with platform-specific
implementations in platform_sensor_provider_*.cc files. The one in this patch
could be called platform_sensor_provider_default.cc.

[Mikhail, 2016/08/19 19:10:02]

I was considering using of Singleton, but here I beleive it is not beneficial as
we have singleton and factory at the same time, now it's gonna be
 	
PlatformSensorProvider* PlatformSensorProvider::GetInstance() {
if (!s_instance_) {
#if PLATFORM(ANDROID)
s_instance_ = new PlatformSensorProviderAndroid();
#elif PLATFORM(WIN)
s_instance_ = new PlatformSensorProviderWin();
#endif
}
return s_instance_;
}

with Singleton this requires custom traits class which IMO is an overkill.

[timvolodine, 2016/08/22 18:42:46]

There is no need for #ifdefs when you follow the standard practice for
multi-platform implementations in chromium using "split the implementation"
approach described in
https://www.chromium.org/developers/design-documents/conventions-and-patterns...

There are many examples in the code base as well (e.g. device/sensors,
device/battery to name a few).

[Mikhail, 2016/08/22 19:16:15]

Thanks for the links! so the solution could be to add to each of the platform
specific files its own "PlatformSensorProvider::GetInstance()" definition, this
is indeed more elegant and allows to get rid of #ifdefs. I'll update the patch
accordingly.

[timvolodine, 2016/08/22 19:42:25]

yes please, thanks ;)

+}
+
+PlatformSensorProvider::PlatformSensorProvider() = default;
+PlatformSensorProvider::~PlatformSensorProvider() = default;
+
+scoped_refptr<PlatformSensor> PlatformSensorProvider::CreateSensor(
+    mojom::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;
+
+  scoped_refptr<PlatformSensor> new_sensor =
+      CreateSensorInternal(type, std::move(mapping), size);
+  if (!new_sensor)
+    return nullptr;
+
+  DCHECK(!ContainsKey(sensor_map_, type));
+  sensor_map_[type] = new_sensor.get();
+
+  return new_sensor;
+}
+
+scoped_refptr<PlatformSensor> PlatformSensorProvider::GetSensor(
+    mojom::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;
+
+  shared_buffer_handle_ =
+      mojo::SharedBufferHandle::Create(kSharedBufferSizeInBytes);
+  return shared_buffer_handle_.is_valid();
+}
+
+void PlatformSensorProvider::RemoveSensor(mojom::SensorType type) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(ContainsKey(sensor_map_, type));
+  sensor_map_.erase(type);
+
+  if (sensor_map_.empty())
+    shared_buffer_handle_.reset();
+}
+
+mojo::ScopedSharedBufferHandle
+PlatformSensorProvider::CloneSharedBufferHandle() {
+  DCHECK(CalledOnValidThread());
+  CreateSharedBufferIfNeeded();
+  return shared_buffer_handle_->Clone();
+}
+
+}  // namespace device