Android在标准linux基础上对休眠唤醒的实现(三)

四、android层源码解析

在linux之上经过android的软件堆层层封装,最终在上层的java应用程序中使用。休眠唤醒也是从最上层发出的命令，然后一层一层地将参数解析，往最底层传，最后走上标准linux的休眠唤醒之路。

这一部分将会初略分析休眠唤醒机制上linux之上所走的路线。

在linux之上，存在一个hal层，专门做和linux内核设备打交道的事情，这里也不例外。休眠唤醒机制的hal层源码位于：@hardware/libhardware_legacy/power/power.c

该文件源码比较简单，下面列举重点片段：

enum { ACQUIRE_PARTIAL_WAKE_LOCK = 0, RELEASE_WAKE_LOCK, REQUEST_STATE, OUR_FD_COUNT }; const char * const NEW_PATHS[] = { "/sys/power/wake_lock", "/sys/power/wake_unlock", "/sys/power/state" }; static int g_initialized = 0; static int g_fds[OUR_FD_COUNT]; static const char *off_state = "mem"; static const char *on_state = "on"; static int open_file_descriptors(const char * const paths[]) { int i; for (i=0; i<OUR_FD_COUNT; i++) { int fd = open(paths[i], O_RDWR); if (fd < 0) { fprintf(stderr, "fatal error opening /"%s/"/n", paths[i]); g_error = errno; return -1; } g_fds[i] = fd; } g_error = 0; return 0; } static inline void initialize_fds(void) { if (g_initialized == 0) { if(open_file_descriptors(NEW_PATHS) < 0) { open_file_descriptors(OLD_PATHS); on_state = "wake"; off_state = "standby"; } g_initialized = 1; } } int acquire_wake_lock(int lock, const char* id) { initialize_fds(); if (g_error) return g_error; int fd; if (lock == PARTIAL_WAKE_LOCK) { // 上层传下来的lock type fd = g_fds[ACQUIRE_PARTIAL_WAKE_LOCK]; } else { return EINVAL; } return write(fd, id, strlen(id)); } int release_wake_lock(const char* id) { initialize_fds(); // LOGI("release_wake_lock id='%s'/n", id); if (g_error) return g_error; ssize_t len = write(g_fds[RELEASE_WAKE_LOCK], id, strlen(id)); return len >= 0; } int set_screen_state(int on) { QEMU_FALLBACK(set_screen_state(on)); LOGI("*** set_screen_state %d", on); initialize_fds(); if (g_error) return g_error; char buf[32]; int len; if(on) len = sprintf(buf, on_state); else len = sprintf(buf, off_state); len = write(g_fds[REQUEST_STATE], buf, len); if(len < 0) { LOGE("Failed setting last user activity: g_error=%d/n", g_error); } return 0; }

Hal层的代码在jni层中被使用，源码位于：frameworks/base/core/jni/android_os_Power.cpp，代码片段如下：

static void acquireWakeLock(JNIEnv *env, jobject clazz, jint lock, jstring idObj) { if (idObj == NULL) { throw_NullPointerException(env, "id is null"); return ; } const char *id = env->GetStringUTFChars(idObj, NULL); acquire_wake_lock(lock, id); env->ReleaseStringUTFChars(idObj, id); }// 对wakelock加锁函数 static void releaseWakeLock(JNIEnv *env, jobject clazz, jstring idObj) { if (idObj == NULL) { throw_NullPointerException(env, "id is null"); return ; } const char *id = env->GetStringUTFChars(idObj, NULL); release_wake_lock(id); env->ReleaseStringUTFChars(idObj, id); }// 对wakelock解锁函数 static int setScreenState(JNIEnv *env, jobject clazz, jboolean on) { return set_screen_state(on); }// 休眠唤醒的函数

Jni的方法需要注册到上层才可以使用，同时也需要在上层的对应java类中声明了native才可以使用。那么这里的方法在java中对应的声明在哪里呢？frameworks/base/core/java/android/os/Power.java，该文件定义一个java类，如下：

public class Power { // can't instantiate this class private Power() { } /** * Wake lock that ensures that the CPU is running. The screen might * not be on. */ public static final int PARTIAL_WAKE_LOCK = 1; /** * Wake lock that ensures that the screen is on. */ public static final int FULL_WAKE_LOCK = 2; public static native void acquireWakeLock(int lock, String id); public static native void releaseWakeLock(String id); … /** * Turn the screen on or off * * @param on Whether you want the screen on or off */ public static native int setScreenState(boolean on); … }

声明的jni接口应该是被java server在使用，这里就是专门的电源管理服务：PowerManagerService使用，具体源码位置在：frameworks/base/services/java/com/android/server/PowerManagerService.java。android在最上层还提供了现场的android.os.PowerManager类

(frameworks/base/core/java/android/os/PowerManager.java)来供app使用，PowerManager类会调用java服务PowerManagerService的方法来完成与wakelock相关的工作。

@ frameworks/base/core/java/android/os/PowerManager.java

类PowerManager中内嵌了一个WakeLock类，另外还定义了wakelock的类型，下面是代码片段：

public class PowerManager { private static final String TAG = "PowerManager"; … /** * Wake lock that ensures that the CPU is running. The screen might * not be on. */ public static final int PARTIAL_WAKE_LOCK = WAKE_BIT_CPU_STRONG; /** * Wake lock that ensures that the screen and keyboard are on at * full brightness. */ public static final int FULL_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_BRIGHT | WAKE_BIT_KEYBOARD_BRIGHT; /** * Wake lock that ensures that the screen is on at full brightness; * the keyboard backlight will be allowed to go off. */ public static final int SCREEN_BRIGHT_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_BRIGHT; /** * Wake lock that ensures that the screen is on (but may be dimmed); * the keyboard backlight will be allowed to go off. */ public static final int SCREEN_DIM_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_DIM; /** * Wake lock that turns the screen off when the proximity sensor activates. * Since not all devices have proximity sensors, use * {@link #getSupportedWakeLockFlags() getSupportedWakeLockFlags()} to determine if * this wake lock mode is supported. * * {@hide} */ public static final int PROXIMITY_SCREEN_OFF_WAKE_LOCK = WAKE_BIT_PROXIMITY_SCREEN_OFF; … public class WakeLock { … WakeLock(int flags, String tag) { switch (flags & LOCK_MASK) { case PARTIAL_WAKE_LOCK: case SCREEN_DIM_WAKE_LOCK: case SCREEN_BRIGHT_WAKE_LOCK: case FULL_WAKE_LOCK: case PROXIMITY_SCREEN_OFF_WAKE_LOCK: break; default: throw new IllegalArgumentException(); } mFlags = flags; mTag = tag; mToken = new Binder(); } public void acquire() { synchronized (mToken) { if (!mRefCounted || mCount++ == 0) { try { mService.acquireWakeLock(mFlags, mToken, mTag); } catch (RemoteException e) { } mHeld = true; } } } public void release(int flags) { synchronized (mToken) { if (!mRefCounted || --mCount == 0) { try { mService.releaseWakeLock(mToken, flags); } catch (RemoteException e) { } mHeld = false; } if (mCount < 0) { throw new RuntimeException("WakeLock under-locked " + mTag); } } } … } … public WakeLock newWakeLock(int flags, String tag) { if (tag == null) { throw new NullPointerException("tag is null in PowerManager.newWakeLock"); } return new WakeLock(flags, tag); } public void goToSleep(long time) { try { mService.goToSleep(time); } catch (RemoteException e) { } } … public PowerManager(IPowerManager service, Handler handler) { mService = service; mHandler = handler; } IPowerManager mService; Handler mHandler; }

应用实例：

PowerManager pm = (PowerManager)getSystemService(Context.POWER_SERVICE); PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, “Tag”); wl.acquire(); //申请锁这个里面会调用PowerManagerService里面acquireWakeLock() … wl.release(); //释放锁，显示的释放，如果申请的锁不在此释放系统就不会进入休眠。

接下来就会调用到java服务PowerManagerService中：

public void acquireWakeLock(int flags, IBinder lock, String tag) { int uid = Binder.getCallingUid(); if (uid != Process.myUid()) { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.WAKE_LOCK, null); } long ident = Binder.clearCallingIdentity(); try { synchronized (mLocks) { acquireWakeLockLocked(flags, lock, uid, tag); // 内部方法 } } finally { Binder.restoreCallingIdentity(ident); } } acquireWakeLockLocked(flags, lock, uid, tag)会调用函数power类的方法： Power.acquireWakeLock(Power.PARTIAL_WAKE_LOCK,PARTIAL_NAME)。 public void releaseWakeLock(IBinder lock, int flags) { int uid = Binder.getCallingUid(); if (uid != Process.myUid()) { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.WAKE_LOCK, null); } synchronized (mLocks) { releaseWakeLockLocked(lock, flags, false); } }

releaseWakeLockLocked(lock, flags, false)函数会调用power类的方法：

Power.releaseWakeLock(PARTIAL_NAME);

上层休眠唤醒都是调用PowerManagerService类的方法：

goToSleep()

à goToSleepWithReason()

à goToSleepLocked()

à setPowerState()

à setScreenStateLocked()

à Power.setScreenState()

à jni方法

Android层的代码分析得不是很详细，这里只关注框架和流程。下图是网上的一个框架,可以参考一下: