【Android休眠】之休眠锁的获取和释放

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受不了xxxx恶心人的行为，遂搬迁至博客园。 始发：2016-12-16 13:11:41   版本信息： Linux：3.10 Android：4.4

 

一、PowerManagerService

引起休眠动作（进入休眠前执行一些必要的操作）的事件有两个：

• PowerKey事件，通过JNI调用PowerManagerService中的goToSleepFromNative()方法
• Timeout，指【设置->显示->休眠】中设置的Timeout数值

Android休眠在PowerManagerService中的流程如下图：

图示：最终都会调用到updatePowerStateLocked()方法，在更新一些标志的状态、发送休眠通知后，调用updateSuspendBlockerLocked()执行休眠锁的释放动作。

 

二、PowerManagerService中Timeout处理流程

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/**  * PowerManagerService设置了很多的标志位，用来标识某个事件的状态是否发生改变，比如：  * DIRTY_SETTINGS，一旦系统设置发生变化，DIRTY_SETTINGS位就会被设置，  * 处理函数检测到DIRTY_SETTINGS被置位，就进行相应的动作  * dirty：包含了所有发生变化的标志  */ private void updateUserActivitySummaryLocked(long now, int dirty) {     // Update the status of the user activity timeout timer.     if ((dirty & (DIRTY_USER_ACTIVITY | DIRTY_WAKEFULNESS | DIRTY_SETTINGS)) != 0) {         // 1、消息队列中含有尚未处理的MSG_USER_ACTIVITY_TIMEOUT，就移除，避免重复进入休眠操作         mHandler.removeMessages(MSG_USER_ACTIVITY_TIMEOUT);            long nextTimeout = 0;         // 2、mWakefulness != WAKEFULNESS_ASLEEP：当前醒着         if (mWakefulness != WAKEFULNESS_ASLEEP) {             // 3、获取Timeout的值，比如30s             final int screenOffTimeout = getScreenOffTimeoutLocked();             // 屏幕在熄灭前，会先变暗一段时间，这段时间叫DimDuration，计算方式：             // SCREEN_DIM_DURATION = 7s，MAXIMUM_SCREEN_DIM_RATIO = 0.2             // Math.min(SCREEN_DIM_DURATION, (int)(screenOffTimeout * MAXIMUM_SCREEN_DIM_RATIO))             // 4、获取DimDuration的值，30s x 0.2 = 6s             final int screenDimDuration = getScreenDimDurationLocked(screenOffTimeout);                mUserActivitySummary = 0;             // 5、mLastUserActivityTime >= mLastWakeTime： 用户最后使用机器的时间在上次唤醒时间之后             if (mLastUserActivityTime >= mLastWakeTime) {                 // nextTimeout：此处指到屏幕Dim的时间间隔                 // 6、nextTimeout的时间：BASE + 30 - 6 = BASE + 24                 nextTimeout = mLastUserActivityTime                         + screenOffTimeout - screenDimDuration;                 if (now < nextTimeout) {                     // now在屏幕Dim之前，说明屏幕亮着，设置flag                     mUserActivitySummary |= USER_ACTIVITY_SCREEN_BRIGHT;                 } else {                     // extTimeout：此处指到屏幕熄灭的时间间隔                     //7、nextTimeout的时间：BASE + 30 = BASE + 30                     nextTimeout = mLastUserActivityTime + screenOffTimeout;                     // 8、now处于屏幕Dim之后、屏幕熄灭之前设置DIM flag                     if (now < nextTimeout) {                         mUserActivitySummary |= USER_ACTIVITY_SCREEN_DIM;                     }                 }             }             if (mUserActivitySummary == 0                     && mLastUserActivityTimeNoChangeLights >= mLastWakeTime) {                 nextTimeout = mLastUserActivityTimeNoChangeLights + screenOffTimeout;                 if (now < nextTimeout                         && mDisplayPowerRequest.screenState                                 != DisplayPowerRequest.SCREEN_STATE_OFF) {                     mUserActivitySummary = mDisplayPowerRequest.screenState                             == DisplayPowerRequest.SCREEN_STATE_BRIGHT ?                             USER_ACTIVITY_SCREEN_BRIGHT : USER_ACTIVITY_SCREEN_DIM;                 }             }             // mUserActivitySummary发生了改变             if (mUserActivitySummary != 0) {                 Message msg = mHandler.obtainMessage(MSG_USER_ACTIVITY_TIMEOUT);                 Slog.i(TAG, "updateUserActivitySummaryLocked, send MSG_USER_ACTIVITY_TIMEOUT");                 msg.setAsynchronous(true);                 mHandler.sendMessageAtTime(msg, nextTimeout);             }         } else {             mUserActivitySummary = 0;         }     } }

 

SG_USER_ACTIVITY_TIMEOUT事件处理：

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private final class PowerManagerHandler extends Handler {     @Override     public void handleMessage(Message msg) {         switch (msg.what) {         case MSG_USER_ACTIVITY_TIMEOUT:             handleUserActivityTimeout();             break;     } }    /**  * Called when a user activity timeout has occurred.  * Simply indicates that something about user activity has changed so that the new  * state can be recomputed when the power state is updated.  */ private void handleUserActivityTimeout() { // runs on handler thread     mDirty |= DIRTY_USER_ACTIVITY;     updatePowerStateLocked(); }

　　

三、PowerManagerService中休眠锁的获取/释放

这部分代码清晰，直接看下：

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private void updatePowerStateLocked() {     if (!mSystemReady || mDirty == 0) {         return;     }     // Phase 0: Basic state updates.       // Phase 1: Update wakefulness.       // Phase 2: Update dreams and display power state.       // Phase 3: Send notifications, if needed.       // Phase 4: Update suspend blocker.     // Because we might release the last suspend blocker here, we need to make sure     // we finished everything else first!     updateSuspendBlockerLocked(); }   /**  * Updates the suspend blocker that keeps the CPU alive.  */ private void updateSuspendBlockerLocked() {     final boolean needWakeLockSuspendBlocker = ((mWakeLockSummary & WAKE_LOCK_CPU) != 0);     final boolean needDisplaySuspendBlocker = needDisplaySuspendBlocker();       // First acquire suspend blockers if needed.     if (needWakeLockSuspendBlocker && !mHoldingWakeLockSuspendBlocker) {         mWakeLockSuspendBlocker.acquire();         mHoldingWakeLockSuspendBlocker = true;     }     if (needDisplaySuspendBlocker && !mHoldingDisplaySuspendBlocker) {         mDisplaySuspendBlocker.acquire();         mHoldingDisplaySuspendBlocker = true;     }       // Then release suspend blockers if needed.     if (!needWakeLockSuspendBlocker && mHoldingWakeLockSuspendBlocker) {         mWakeLockSuspendBlocker.release();         mHoldingWakeLockSuspendBlocker = false;     }     if (!needDisplaySuspendBlocker && mHoldingDisplaySuspendBlocker) {         mDisplaySuspendBlocker.release();         mHoldingDisplaySuspendBlocker = false;     } }   private final class SuspendBlockerImpl implements SuspendBlocker {     private final String mName;     private int mReferenceCount;       public SuspendBlockerImpl(String name) {         mName = name;     }       @Override     public void acquire() {         synchronized (this) {             mReferenceCount += 1;             if (mReferenceCount == 1) {                 nativeAcquireSuspendBlocker(mName);             }         }     }       @Override     public void release() {         synchronized (this) {             mReferenceCount -= 1;             if (mReferenceCount == 0) {                    nativeReleaseSuspendBlocker(mName);             }         }     } }

　　

休眠锁的获取和释放，最终通过JNI方式读写/sys/power/wake_lock、/sys/power/wake_unlock：

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// 1、JNI接口 com_android_server_power_PowerManagerService.cpp (frameworks\base\services\jni) static void nativeAcquireSuspendBlocker(JNIEnv *env, jclass clazz, jstring nameStr) {     ScopedUtfChars name(env, nameStr);     acquire_wake_lock(PARTIAL_WAKE_LOCK, name.c_str()); }   // 2、定义要操作的文件 power.c (hardware\libhardware_legacy\power) const char *const NEW_PATHS[] = {     "/sys/power/wake_lock",     "/sys/power/wake_unlock", };   // 3、初始化设备节点 static inline void initialize_fds(void) {     if (g_initialized == 0) {         if(open_file_descriptors(NEW_PATHS) < 0)             open_file_descriptors(OLD_PATHS);         g_initialized = 1;     } }   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; }   // 4、id即为锁的名字，之后就是读写设备 int acquire_wake_lock(int lock, const char* id) {     initialize_fds();       if (g_error) return g_error;       int fd;       if (lock == PARTIAL_WAKE_LOCK) {         fd = g_fds[ACQUIRE_PARTIAL_WAKE_LOCK];     } else {         return EINVAL;     }       return write(fd, id, strlen(id)); }