Add RELATIVE_ORIENTATION sensor implementation on macOS to //device/generic_sensor

device/generic_sensor/public/cpp/sensor_reading.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/public/cpp/sensor_reading.h"
 
+#include "device/base/synchronization/shared_memory_seqlock_buffer.h"
+
+namespace {

[timvolodine, 2017/06/21 18:22:11]

looks like this is a merge from a different patch
https://chromium-review.googlesource.com/c/541685/ ?
(also below and corresp .h file)

[juncai, 2017/07/20 00:22:16]

This buffer reading functionality is moved to SensorReadingSharedBufferReader.

+
+constexpr int kMaxReadAttemptsCount = 10;
+
+bool TryReadFromBuffer(const device::SensorReadingSharedBuffer* buffer,
+                       device::SensorReading* result) {
+  const device::OneWriterSeqLock& seqlock = buffer->seqlock.value();
+  auto version = seqlock.ReadBegin();
+  auto reading_data = buffer->reading;
+  if (seqlock.ReadRetry(version))
+    return false;
+  *result = reading_data;
+  return true;
+}
+
+}  // namespace
+
 namespace device {
 
 SensorReading::SensorReading() = default;
 SensorReading::SensorReading(const SensorReading& other) = default;
 SensorReading::~SensorReading() = default;
 
 SensorReadingSharedBuffer::SensorReadingSharedBuffer() = default;
 SensorReadingSharedBuffer::~SensorReadingSharedBuffer() = default;
 
 // static
 uint64_t SensorReadingSharedBuffer::GetOffset(mojom::SensorType type) {
   return (static_cast<uint64_t>(mojom::SensorType::LAST) -
           static_cast<uint64_t>(type)) *
          sizeof(SensorReadingSharedBuffer);
 }
 
+bool GetSensorReadingFromBuffer(const SensorReadingSharedBuffer* buffer,
+                                SensorReading* result) {
+  int read_attempts = 0;
+  while (!TryReadFromBuffer(buffer, result)) {
+    if (++read_attempts == kMaxReadAttemptsCount)
+      return false;
+  }
+
+  return true;
+}
+
 }  // namespace device