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。
Year
Cores
Clock
RAM
2008
1
528MHz
192MB
2009
n/a
600MHz
290MB
2010
n/a
1.0GHz
512MB
2011
2
1.2GHz
1GB
2012
4
1.5GHz
1.5GB
2013
n/a
2.0GHz
2GB
2014
n/a
>2GHz
>2GB
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 cpud+。
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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