如何获取 Android 设备的CPU核数、时钟频率以及内存大小

因项目需要，分析了一下 Facebook 的开源项目 - Device Year Class。

Device Year Class 的主要功能是根据 CPU核数、时钟频率 以及 内存大小 对设备进行分级。代码很简单，只包含两个类:

• DeviceInfo -> 获取设备参数，
• YearClass -> 根据参数进行分级。

下表是 Facebook 公司提供的分级标准，其中 Year 栏表示分级结果。

关于输出年份的计算方法可以参考源码，本文只把一些比较常用的功能抽取出来做一个简要介绍。

获取 CPU 核数

我们都知道，Linux 中的设备都是以文件的形式存在，CPU 也不例外，因此 CPU 的文件个数就等价与核数。

Android 的 CPU 设备文件位于 /sys/devices/system/cpu/ 目录，文件名的的格式为 cpu\d+。

root@generic_x86_64:/sys/devices/system/cpu # ls
cpu0
cpufreq
cpuidle
kernel_max
modalias
offline
online
possible
power
present
uevent

统计一下文件个数便可以获得 CPU 核数。

public static int getNumberOfCPUCores() {
  if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.GINGERBREAD_MR1) {
    // Gingerbread doesn‘t support giving a single application access to both cores, but a
    // handful of devices (Atrix 4G and Droid X2 for example) were released with a dual-core
    // chipset and Gingerbread; that can let an app in the background run without impacting
    // the foreground application. But for our purposes, it makes them single core.
    return 1;
  }
  int cores;
  try {
    cores = new File("/sys/devices/system/cpu/").listFiles(CPU_FILTER).length;
  } catch (SecurityException e) {
    cores = DEVICEINFO_UNKNOWN;
  } catch (NullPointerException e) {
    cores = DEVICEINFO_UNKNOWN;
  }
  return cores;
}

private static final FileFilter CPU_FILTER = new FileFilter() {
  @Override
  public boolean accept(File pathname) {
    String path = pathname.getName();
    //regex is slow, so checking char by char.
    if (path.startsWith("cpu")) {
      for (int i = 3; i < path.length(); i++) {
        if (path.charAt(i) < ‘0‘ || path.charAt(i) > ‘9‘) {
          return false;
        }
      }
      return true;
    }
    return false;
  }
};

获取时钟频率

获取时钟频率需要读取系统文件 - /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq 或者 /proc/cpuinfo。

我的 Android 模拟器中并没有 cpuinfo_max_freq 文件，因此只能读取 /proc/cpuinfo。

/proc/cpuinfo 包含了很多 cpu 数据。

processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 70
model name  : Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz
stepping    : 1
cpu MHz     : 0.000
cache size  : 1024 KB
fdiv_bug    : no
hlt_bug     : no
f00f_bug    : no
coma_bug    : no
fpu     : yes
fpu_exception   : yes
cpuid level : 4
wp      : yes

代码如下：

public static int getCPUMaxFreqKHz() {
  int maxFreq = DEVICEINFO_UNKNOWN;
  try {
    for (int i = 0; i < getNumberOfCPUCores(); i++) {
      String filename =
          "/sys/devices/system/cpu/cpu" + i + "/cpufreq/cpuinfo_max_freq";
      File cpuInfoMaxFreqFile = new File(filename);
      if (cpuInfoMaxFreqFile.exists()) {
        byte[] buffer = new byte[128];
        FileInputStream stream = new FileInputStream(cpuInfoMaxFreqFile);
        try {
          stream.read(buffer);
          int endIndex = 0;
          //Trim the first number out of the byte buffer.
          while (buffer[endIndex] >= ‘0‘ && buffer[endIndex] <= ‘9‘
              && endIndex < buffer.length) endIndex++;
          String str = new String(buffer, 0, endIndex);
          Integer freqBound = Integer.parseInt(str);
          if (freqBound > maxFreq) maxFreq = freqBound;
        } catch (NumberFormatException e) {
          //Fall through and use /proc/cpuinfo.
        } finally {
          stream.close();
        }
      }
    }
    if (maxFreq == DEVICEINFO_UNKNOWN) {
      FileInputStream stream = new FileInputStream("/proc/cpuinfo");
      try {
        int freqBound = parseFileForValue("cpu MHz", stream);
        freqBound *= 1000; //MHz -> kHz
        if (freqBound > maxFreq) maxFreq = freqBound;
      } finally {
        stream.close();
      }
    }
  } catch (IOException e) {
    maxFreq = DEVICEINFO_UNKNOWN; //Fall through and return unknown.
  }
  return maxFreq;
}

获取内存大小

如果 SDK 版本大于等于 JELLY_BEAN ，可以通过 ActivityManager 来获取内从大小。

ActivityManager.MemoryInfo memInfo = new ActivityManager.MemoryInfo();
ActivityManager am = (ActivityManager) c.getSystemService(Context.ACTIVITY_SERVICE);
am.getMemoryInfo(memInfo);

如果版本低于 JELLY_BEAN ，则只能读取系统文件了。

FileInputStream stream = new FileInputStream("/proc/meminfo");
totalMem = parseFileForValue("MemTotal", stream);

完整代码如下：

@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
public static long getTotalMemory(Context c) {
  // memInfo.totalMem not supported in pre-Jelly Bean APIs.
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
    ActivityManager.MemoryInfo memInfo = new ActivityManager.MemoryInfo();
    ActivityManager am = (ActivityManager) c.getSystemService(Context.ACTIVITY_SERVICE);
    am.getMemoryInfo(memInfo);
    if (memInfo != null) {
      return memInfo.totalMem;
    } else {
      return DEVICEINFO_UNKNOWN;
    }
  } else {
    long totalMem = DEVICEINFO_UNKNOWN;
    try {
      FileInputStream stream = new FileInputStream("/proc/meminfo");
      try {
        totalMem = parseFileForValue("MemTotal", stream);
        totalMem *= 1024;
      } finally {
        stream.close();
      }
    } catch (IOException e) {
    }
    return totalMem;
  }
}

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