chromeos: Add CPU temperature reader

chromeos/system/cpu_temperature_reader.h

Index: chromeos/system/cpu_temperature_reader.h
diff --git a/chromeos/system/cpu_temperature_reader.h b/chromeos/system/cpu_temperature_reader.h
new file mode 100644
index 0000000000000000000000000000000000000000..c31f0defaa702641e20febb0c4409aec0d33d361
--- /dev/null
+++ b/chromeos/system/cpu_temperature_reader.h
@@ -0,0 +1,57 @@
+// Copyright 2017 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.
+
+#ifndef CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_
+#define CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/macros.h"
+
+namespace chromeos {
+namespace system {
+
+// Used to read CPU temperature info from sysfs hwmon.
+class CPUTemperatureReader {
+ public:
+  // Contains info from a CPU temperature sensor.
+  struct CPUTemperatureInfo {

[Daniel Erat, 2017/04/21 21:01:20]

i think you need to declare a c'tor and d'tor here (and define them in the .cc
file with "= default;" since this struct has a non-POD member

[Simon Que, 2017/04/24 13:59:17]

Done.

+    // The temperature read by a CPU temperature sensor in degrees Celsius.
+    double temp_celsius;
+
+    // The name of the CPU temperature zone monitored by this sensor. Used to
+    // identify the source of each temperature reading. Taken from sysfs "name"
+    // or "label" field, if it exists.
+    std::string label;
+
+    bool operator<(const CPUTemperatureInfo& other) const {

[Daniel Erat, 2017/04/21 21:01:20]

move this method above the members; also move the definition (and <utility>
include) to the .cc file

[Simon Que, 2017/04/24 13:59:17]

Done.

+      return std::make_pair(temp_celsius, label) <

[Daniel Erat, 2017/04/21 21:01:20]

sorting by temperature is a bit surprising. consider comparing label first
instead

[Simon Que, 2017/04/24 13:59:17]

Done.

+             std::make_pair(other.temp_celsius, label);
+    }
+  };
+
+  CPUTemperatureReader();
+

[Daniel Erat, 2017/04/21 21:01:20]

nit: delete blank line here

[Simon Que, 2017/04/24 13:59:17]

Done.

+  ~CPUTemperatureReader();
+
+  void set_hwmon_dir_for_test(const std::string& dir) { hwmon_dir_ = dir; }
+
+  // Read temperature from each thermal sensor of the CPU. Returns a vector
+  // containing a reading from each sensor to |callback|. This is a blocking

[Daniel Erat, 2017/04/21 21:01:20]

fix comment; there's no callback now. also s/Read/Reads/ in first sentence since
that's the form usually used in chrome method comments

[Simon Que, 2017/04/24 13:59:17]

Done.

+  // function that should be run on a thread that allows blocking operations.
+  std::vector<CPUTemperatureInfo> GetCPUTemperatures();
+
+ private:
+  // Sysfs hwmon directory path.
+  std::string hwmon_dir_;
+
+  DISALLOW_COPY_AND_ASSIGN(CPUTemperatureReader);
+};
+
+}  // namespace system
+}  // namespace chromeos
+
+#endif  // CHROMEOS_SYSTEM_CPU_TEMPERATURE_READER_H_