chromeos: Add CPU temperature reader

chromeos/system/cpu_temp_reader.h

Index: chromeos/system/cpu_temp_reader.h
diff --git a/chromeos/system/cpu_temp_reader.h b/chromeos/system/cpu_temp_reader.h
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index 0000000000000000000000000000000000000000..77f711ab544aa205f98573fc2d2dc75c0826527f
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+++ b/chromeos/system/cpu_temp_reader.h
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+// 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_TEMP_READER_H_
+#define CHROMEOS_SYSTEM_CPU_TEMP_READER_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/macros.h"
+
+namespace chromeos {
+namespace system {
+
+// Contains info from a CPU temperature sensor.
+struct CPUTemperatureInfo {

[stevenjb, 2017/04/17 16:49:00]

Make this a member of the class.

[Simon Que, 2017/04/17 17:07:48]

Done.

+  // The temperature read by a CPU temperature sensor in degrees Celsius.
+  double temp_celsius;

[stevenjb, 2017/04/17 16:49:00]

blank line

[Simon Que, 2017/04/17 17:07:48]

Done.

+  // 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 {
+    return std::make_pair(temp_celsius, label) <
+           std::make_pair(other.temp_celsius, label);
+  }
+};
+
+// Used to read CPU temperature info from sysfs hwmon.
+class CPUTemperatureReader {

[stevenjb, 2017/04/17 16:49:00]

File name should match the class name.

[Simon Que, 2017/04/17 17:07:48]

Done.

+ public:
+  CPUTemperatureReader();
+
+  // Read temperature from each thermal sensor of the CPU. Returns a vector
+  // containing a reading from each sensor.
+  //
+  // This is a blocking function that performs file operations. Users of this
+  // function can choose to call it from a task runner instead.

[stevenjb, 2017/04/17 16:49:00]

Instead of what? Implemented this way, callers *must* call it from a blocking
task runner.

[Simon Que, 2017/04/17 17:07:48]

Do you have an example of Chrome code that does non-blocking file I/O? 

[stevenjb, 2017/04/17 17:24:40]

I'm not sure what you mean. There is no such thing.

The point I am trying to make is that the fact that this method does blocking IO
is largely an implementation detail. We should either:

a) Allow this to be called form the main/UI thread (and make it async).
b) Clarify the comment, i.e.
"This is a blocking function that performs file operations. It must be called
from a task runner with MayBlock() set."

+  std::vector<CPUTemperatureInfo> GetCPUTemperatures();
+
+  void set_hwmon_dir_for_test(const std::string& dir) { hwmon_dir_ = dir; }
+
+ private:
+  // Sysfs hwmon directory path. Gets initialized to a default value but can be
+  // overriden by set_hwmon_dir_for_test().
+  std::string hwmon_dir_;
+
+  DISALLOW_COPY_AND_ASSIGN(CPUTemperatureReader);
+};
+
+}  // namespace system
+}  // namespace chromeos
+
+#endif  // CHROMEOS_SYSTEM_CPU_TEMP_READER_H_