Added a few more methods to detect number of CPU cores on device

yearclass/src/main/java/com/facebook/device/yearclass/DeviceInfo.java

@@ -27,7 +27,9 @@ public class DeviceInfo {
   public static final int DEVICEINFO_UNKNOWN = -1;
 
   /**
-   * Reads the number of CPU cores from {@code /sys/devices/system/cpu/}.
+   * Reads the number of CPU cores from the first available information from
+   * {@code /sys/devices/system/cpu/possible}, {@code /sys/devices/system/cpu/present},
+   * then {@code /sys/devices/system/cpu/}.
    *
    * @return Number of CPU cores in the phone, or DEVICEINFO_UKNOWN = -1 in the event of an error.
    */
@@ -41,7 +43,13 @@ public static int getNumberOfCPUCores() {
     }
     int cores;
     try {
-      cores = new File("/sys/devices/system/cpu/").listFiles(CPU_FILTER).length;
+      cores = getCoresFromFileInfo("/sys/devices/system/cpu/possible");
+      if (cores == DEVICEINFO_UNKNOWN) {
+        cores = getCoresFromFileInfo("/sys/devices/system/cpu/present");
+      }
+      if (cores == DEVICEINFO_UNKNOWN) {
+        cores = getCoresFromCPUFileList();
+      }
     } catch (SecurityException e) {
       cores = DEVICEINFO_UNKNOWN;
     } catch (NullPointerException e) {
@@ -50,6 +58,39 @@ public static int getNumberOfCPUCores() {
     return cores;
   }
 
+  /**
+   * Tries to read file contents from the file location to determine the number of cores on device.
+   * @param fileLocation The location of the file with CPU information
+   * @return Number of CPU cores in the phone, or DEVICEINFO_UKNOWN = -1 in the event of an error.
+   */
+  private static int getCoresFromFileInfo(String fileLocation) {
+    try {
+      InputStream is = new FileInputStream(fileLocation);
+      BufferedReader buf = new BufferedReader(new InputStreamReader(is));
+      String fileContents = buf.readLine();
+      return getCoresFromFileString(fileContents);
+    } catch (IOException e) {
+      return DEVICEINFO_UNKNOWN;
+    }
+  }
+
+  /**
+   * Converts from a CPU core information format to number of cores.
+   * @param str The CPU core information string, in the format of "0-N"
+   * @return The number of cores represented by this string
+   */
+  static int getCoresFromFileString(String str) {
+    if (str == null || !str.matches("0-[\\d]+$")) {
+      return DEVICEINFO_UNKNOWN;
+    }
+    int cores = Integer.valueOf(str.substring(2)) + 1;
+    return cores;
+  }
+
+  private static int getCoresFromCPUFileList() {
+    return new File("/sys/devices/system/cpu/").listFiles(CPU_FILTER).length;
+  }
+
   private static final FileFilter CPU_FILTER = new FileFilter() {
     @Override
     public boolean accept(File pathname) {
@@ -209,4 +250,4 @@ private static int extractValue(byte[] buffer, int index) {
     }
     return DEVICEINFO_UNKNOWN;
   }
-}
+}

yearclass/src/test/java/com/facebook/device/yearclass/DeviceInfoTest.java

@@ -0,0 +1,31 @@
+/* Copyright (c) 2015, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+package com.facebook.device.yearclass;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.powermock.modules.junit4.PowerMockRunner;
+
+import static org.junit.Assert.*;
+
+@RunWith(PowerMockRunner.class)
+public class DeviceInfoTest {
+
+    @Test
+    public void testFileStringValid() {
+        assertEquals(DeviceInfo.getCoresFromFileString("0-3"), 4);
+        assertEquals(DeviceInfo.getCoresFromFileString("0-11"), 12);
+    }
+
+    @Test
+    public void testFileStringInvalid() {
+        assertEquals(DeviceInfo.getCoresFromFileString("INVALIDSTRING"), -1);
+        assertEquals(DeviceInfo.getCoresFromFileString("0-2a"), -1);
+        assertEquals(DeviceInfo.getCoresFromFileString("035"), -1);
+    }
+}