Implement querying CPU time from /proc/stat on Linux for systemInfo.cpu API

chrome/browser/extensions/api/system_info_cpu/cpu_info_provider_linux.cc

 // Copyright (c) 2012 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 "chrome/browser/extensions/api/system_info_cpu/cpu_info_provider.h"
 
+#include "base/file_util.h"
+
 namespace extensions {
 
 bool CpuInfoProvider::QueryCpuTimePerProcessor(std::vector<CpuTime>* times) {
-  // TODO(hongbo): Query the cpu time from /proc/stat.
-  return false;
+  if (!times) return false;

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Why the soft failure when times is null? A CHECK seems more appropriate.

[Hongbo Min, 2012/09/16 15:14:43]

No CHECK is used since access violation can help do this when trying to
dereference a NULL pointer.

+
+  times->clear();
+
+  const char* kProcStat = "/proc/stat";

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Move this to an anonymous namespace at the head of the file.

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+  std::string contents, line;

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

"line" isn't used until later, its declaration should be closed to where it's
used.

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+  if (!file_util::ReadFileToString(FilePath(kProcStat), &contents))
+     return false;
+
+  std::istringstream iss(contents);

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Needs an #include.

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+  int count = 0;
+
+  unsigned long long user, nice, sys, idle;

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Use uint64 (see
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Intege...
about when to use the built-in integer types).

Also, it's more idiomatic in Chrome C++ code to have one variable declaration
per line, and to also initialize in the declaration (see
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Local_...)

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+  user = nice = sys = idle = 0;
+
+  while (std::getline(iss, line)) {
+    // Ignore the first line because it is just an aggregated number of

[Mihai Parparita -not on Chrome, 2012/09/16 06:07:47]

Also, given this behavior, you may want to remove the "Note that the first
element is the total aggregated numbers of all logic processors." comment in
cpu_info_provider.h, since it's not actually true.

[Hongbo Min, 2012/09/16 15:14:43]

Done. Correct the comment in the cpu_info_provider.h.

+    // all cpuN lines.
+    if (count++ == 0) continue;
+    if (line.compare(0, 3, "cpu") == 0) {

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Turn this into a "if (line.compare(0, 3, "cpu") != 0) {continue}", so that the
body doesn't have to be indented as far.

[Hongbo Min, 2012/09/16 15:14:43]

Done.

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+      sscanf(line.c_str(), "%*s %llu %llu %llu %llu",

[Mihai Parparita -not on Chrome, 2012/09/16 06:01:22]

Needs an #include

[Hongbo Min, 2012/09/16 15:14:43]

Done.

+             &user, &nice, &sys, &idle);
+
+      CpuTime time;
+      time.kernel = sys;
+      time.user = user + nice;
+      time.idle = idle;
+      times->push_back(time);
+    }
+  }
+
+  return true;
 }
 
 }  // namespace extensions