Android Framework 电源子系统（05）核心方法updatePowerStateLocked分析-3 更新屏保发送通知更新wakelock

该系列文章总纲链接：专题分纲目录 Android Framework 电源子系统

本章关键点总结 & 说明：

本章节主要关注➕ updatePowerStateLocked 方法中更新屏保和发送通知并更新wakelock锁部分即可。该章节主要是对更新屏保和发送通知并更新wakelock锁部分进行详细解读。

PMS核心方法updatePowerStateLocked

updatePowerStateLocked 方法是整个PMS中的核心方法，它用来更新整个电源状态的改变，并进行重新计算。PMS中使用一个int值mDirty作为标志位判断电源状态是否发生变化，当电源状态发生改变时，如亮灭屏、电池状态改变、暗屏…都会调用该方法，它的代码实现如下：

private void updatePowerStateLocked() {//...Trace.traceBegin(Trace.TRACE_TAG_POWER, "updatePowerState");try {// 1 更新基本状态// 1.1 更新mIsPowered，mPlugType，mBatteryLevelupdateIsPoweredLocked(mDirty);// 1.2 更新mStayonupdateStayOnLocked(mDirty);updateScreenBrightnessBoostLocked(mDirty);// 2 更新wakefulness和用户活动final long now = SystemClock.uptimeMillis();int dirtyPhase2 = 0;for (;;) {int dirtyPhase1 = mDirty;dirtyPhase2 |= dirtyPhase1;mDirty = 0;// 2.1 得到当前终端整体的信息，保存到mWakeLockSummary变量中updateWakeLockSummaryLocked(dirtyPhase1);// 2.2 根据用户最后的活动来决定当前屏幕的状态updateUserActivitySummaryLocked(now, dirtyPhase1);// 2.3 判定 第二阶段的电源状态更新是否结束if (!updateWakefulnessLocked(dirtyPhase1)) {break;}}// 3 更新显示设备状态boolean displayBecameReady = updateDisplayPowerStateLocked(dirtyPhase2);// 4 更新屏保状态updateDreamLocked(dirtyPhase2, displayBecameReady);// 5 发送通知 并 更新底层wakelock// 5.1 发送通知if (mDisplayReady) {finishWakefulnessChangeLocked();}// 5.2 更新底层wakelockupdateSuspendBlockerLocked();} finally {Trace.traceEnd(Trace.TRACE_TAG_POWER);}
}

该部分代码共分为5部分，因为篇幅较长，所以拆分成3个章节进行分析。本章节是 4 5部分。

4 更新屏保 updateDreamLocked分析

updateDreamLocked函数主要用于更新屏保状态，当设备进入或者退出屏保的时候都会触发这个方法：

private void updateDreamLocked(int dirty, boolean displayBecameReady) {if ((dirty & (DIRTY_WAKEFULNESS| DIRTY_USER_ACTIVITY| DIRTY_WAKE_LOCKS| DIRTY_BOOT_COMPLETED| DIRTY_SETTINGS| DIRTY_IS_POWERED| DIRTY_STAY_ON| DIRTY_PROXIMITY_POSITIVE| DIRTY_BATTERY_STATE)) != 0 || displayBecameReady) {if (mDisplayReady) {//mDirty满足条件，同时屏幕状态调整完毕，才进入下一步scheduleSandmanLocked();}}
}

这里关键分析 scheduleSandmanLocked，代码实现如下：

private void scheduleSandmanLocked() {if (!mSandmanScheduled) {//让MessageQueue中仅保留一个MSG_SANDMANmSandmanScheduled = true;//由handleSandman处理Message msg = mHandler.obtainMessage(MSG_SANDMAN);msg.setAsynchronous(true);mHandler.sendMessage(msg);}
}

处理该消息使用handleSandman函数，它比较复杂，主要用于决定设备是否应该停留在dreaming或dozing状态。代码如下：

private void handleSandman() { // runs on handler thread//1 是否开始进入屏保final boolean startDreaming;final int wakefulness;synchronized (mLock) {mSandmanScheduled = false;wakefulness = mWakefulness;//当updateWakefulnessLocked判断进入dozing或sleep状态时，//会将mSandmanSummoned置为true//mDisplayReady主要确保前面屏幕状态更新完毕if (mSandmanSummoned && mDisplayReady) {//判断device是否可以dream或dozingstartDreaming = canDreamLocked() || canDozeLocked();mSandmanSummoned = false;} else {startDreaming = false;}}//2 表示是否正在屏保final boolean isDreaming;if (mDreamManager != null) {// Restart the dream whenever the sandman is summoned.//重启屏保if (startDreaming) {//结束旧屏保mDreamManager.stopDream(false /*immediate*/);//开启新屏保mDreamManager.startDream(wakefulness == WAKEFULNESS_DOZING);}//startDream成功后，一般isDreaming就会返回trueisDreaming = mDreamManager.isDreaming();} else {isDreaming = false;}//3 更新屏保状态.synchronized (mLock) {//记录进入屏保时的电池电量if (startDreaming && isDreaming) {mBatteryLevelWhenDreamStarted = mBatteryLevel;}if (mSandmanSummoned || mWakefulness != wakefulness) {return; // wait for next cycle}// Determine whether the dream should continue.if (wakefulness == WAKEFULNESS_DREAMING) {if (isDreaming && canDreamLocked()) {if (mDreamsBatteryLevelDrainCutoffConfig >= 0&& mBatteryLevel < mBatteryLevelWhenDreamStarted- mDreamsBatteryLevelDrainCutoffConfig&& !isBeingKeptAwakeLocked()) {} else {return; // continue dreaming}}// Dream has ended or will be stopped.  Update the power state.if (isItBedTimeYetLocked()) {//休眠goToSleepNoUpdateLocked(SystemClock.uptimeMillis(),PowerManager.GO_TO_SLEEP_REASON_TIMEOUT, 0, Process.SYSTEM_UID);updatePowerStateLocked();} else {//唤醒wakeUpNoUpdateLocked(SystemClock.uptimeMillis(), Process.SYSTEM_UID);updatePowerStateLocked();}//如果处于Doze状态,在power键灭屏时，首次会将wakefulness设置为该值} else if (wakefulness == WAKEFULNESS_DOZING) {if (isDreaming) {return; // continue dozing}//进入asleep状态reallyGoToSleepNoUpdateLocked(SystemClock.uptimeMillis(), Process.SYSTEM_UID);updatePowerStateLocked();}}//如果正处在Dream，则只要触发updatePowerStateLocked(),立即退出Dreamif (isDreaming) {mDreamManager.stopDream(false /*immediate*/);}
}

这里主要分3部分对这段代码进行分析

4.1 决定是否可以进入屏保状态

    ...//1 是否开始进入屏保final boolean startDreaming;final int wakefulness;synchronized (mLock) {mSandmanScheduled = false;wakefulness = mWakefulness;//当updateWakefulnessLocked判断进入dozing或sleep状态时，//会将mSandmanSummoned置为true//mDisplayReady主要确保前面屏幕状态更新完毕if (mSandmanSummoned && mDisplayReady) {//判断device是否可以dream或dozingstartDreaming = canDreamLocked() || canDozeLocked();mSandmanSummoned = false;} else {startDreaming = false;}}...

这段代码主要用于确定设备是否可以看是dreaming。除去前置条件的限制外，此处结果主要由canDreamLocked和canDozeLocked决定。canDreamLocked的实现如下：

private boolean canDreamLocked() {//mWakefulness等于WAKEFULNESS_DREAMINGif (mWakefulness != WAKEFULNESS_DREAMING || !mDreamsSupportedConfig //设备支持dreaming|| !mDreamsEnabledSetting  //设置开关开启|| !mDisplayPowerRequest.isBrightOrDim() //屏幕熄灭|| (mUserActivitySummary & (USER_ACTIVITY_SCREEN_BRIGHT| USER_ACTIVITY_SCREEN_DIM | USER_ACTIVITY_SCREEN_DREAM)) == 0|| !mBootCompleted) {return false;}//不处于唤醒态if (!isBeingKeptAwakeLocked()) {//没充电，电源选项也未配置，不可dreamingif (!mIsPowered && !mDreamsEnabledOnBatteryConfig) {return false;}//没充电，且电池电量过低，不可dreamingif (!mIsPowered&& mDreamsBatteryLevelMinimumWhenNotPoweredConfig >= 0&& mBatteryLevel < mDreamsBatteryLevelMinimumWhenNotPoweredConfig) {return false;}//充电，但电池电量过低，不可dreamingif (mIsPowered&& mDreamsBatteryLevelMinimumWhenPoweredConfig >= 0&& mBatteryLevel < mDreamsBatteryLevelMinimumWhenPoweredConfig) {return false;}}return true;
}

从上面的代码可以看出，充电和未充电分别有一个最低的dreaming电量门限，同时 dreaming除了对终端当前的状态、配置项有关外，在非唤醒状态下还与当前的电池电量有关系。

canDozeLocked的实现简单很多，仅仅是 mWakefulness的一个判断，代码如下：

private boolean canDozeLocked() {return mWakefulness == WAKEFULNESS_DOZING;
}

这个过程就是判定是否可以进入屏保状态。接下来满足条件则进入到屏保状态

4.2 在必要时，进入屏保状态

进入屏保状态后，这一部分就开始进行实际的工作。该部分代码如下：

    ...//2 表示是否正在屏保final boolean isDreaming;if (mDreamManager != null) {// Restart the dream whenever the sandman is summoned.//重启屏保if (startDreaming) {//结束旧屏保mDreamManager.stopDream(false /*immediate*/);//开启新屏保mDreamManager.startDream(wakefulness == WAKEFULNESS_DOZING);}//startDream成功后，一般isDreaming就会返回trueisDreaming = mDreamManager.isDreaming();} else {isDreaming = false;}...

mDreamManager为DreamManagerService的Binder代理。我们重点看看DreamManagerService的startDream函数，stopDream的工作内容与startDream相反。

public void startDream(boolean doze) {startDreamInternal(doze);
}

继续分析startDreamInternal，代码如下：

private void startDreamInternal(boolean doze) {final int userId = ActivityManager.getCurrentUser();//获取屏保对象final ComponentName dream = chooseDreamForUser(doze, userId);if (dream != null) {synchronized (mLock) {startDreamLocked(dream, false /*isTest*/, doze, userId);}}
}

继续分析startDreamLocked，代码如下：

private void startDreamLocked(final ComponentName name,final boolean isTest, final boolean canDoze, final int userId) {//申请的屏保与当前的一致，不用进行修改if (Objects.equal(mCurrentDreamName, name)&& mCurrentDreamIsTest == isTest&& mCurrentDreamCanDoze == canDoze&& mCurrentDreamUserId == userId) {return;}//停止当前屏保stopDreamLocked(true /*immediate*/);final Binder newToken = new Binder();mCurrentDreamToken = newToken;mCurrentDreamName = name;mCurrentDreamIsTest = isTest;mCurrentDreamCanDoze = canDoze;mCurrentDreamUserId = userId;mHandler.post(new Runnable() {@Overridepublic void run() {//调用DreamController的startDream函数mController.startDream(newToken, name, isTest, canDoze, userId);}});
}

继续分析 DreamController 的 startDream 函数，代码实现如下：

public void startDream(Binder token, ComponentName name,boolean isTest, boolean canDoze, int userId) {//移除当前屏保并回调通知stopDream(true /*immediate*/);//...// Close the notification shade. Don't need to send to all, but better to be explicit.mContext.sendBroadcastAsUser(mCloseNotificationShadeIntent, UserHandle.ALL);mCurrentDream = new DreamRecord(token, name, isTest, canDoze, userId);try {//屏幕相关的准备工作mIWindowManager.addWindowToken(token, WindowManager.LayoutParams.TYPE_DREAM);} catch (RemoteException ex) {stopDream(true /*immediate*/);return;}Intent intent = new Intent(DreamService.SERVICE_INTERFACE);intent.setComponent(name);intent.addFlags(Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);try { //拉起屏保服务if (!mContext.bindServiceAsUser(intent, mCurrentDream,Context.BIND_AUTO_CREATE, new UserHandle(userId))) {stopDream(true /*immediate*/);return;}} catch (SecurityException ex) {stopDream(true /*immediate*/);return;}mCurrentDream.mBound = true;//在DREAM_CONNECTION_TIMEOUT到期时，bind服务还未成功，runnable就负责结束dreammHandler.postDelayed(mStopUnconnectedDreamRunnable, DREAM_CONNECTION_TIMEOUT);//...
}

这里所谓的屏保其实就是拉起一个特殊的服务。

4.3 更新屏保状态

    ...//3 更新屏保状态.synchronized (mLock) {//记录进入屏保时的电池电量if (startDreaming && isDreaming) {mBatteryLevelWhenDreamStarted = mBatteryLevel;}if (mSandmanSummoned || mWakefulness != wakefulness) {return; // wait for next cycle}// Determine whether the dream should continue.if (wakefulness == WAKEFULNESS_DREAMING) {if (isDreaming && canDreamLocked()) {if (mDreamsBatteryLevelDrainCutoffConfig >= 0&& mBatteryLevel < mBatteryLevelWhenDreamStarted- mDreamsBatteryLevelDrainCutoffConfig&& !isBeingKeptAwakeLocked()) {} else {return; // continue dreaming}}// Dream has ended or will be stopped.  Update the power state.if (isItBedTimeYetLocked()) {//休眠goToSleepNoUpdateLocked(SystemClock.uptimeMillis(),PowerManager.GO_TO_SLEEP_REASON_TIMEOUT, 0, Process.SYSTEM_UID);updatePowerStateLocked();} else {//唤醒wakeUpNoUpdateLocked(SystemClock.uptimeMillis(), Process.SYSTEM_UID);updatePowerStateLocked();}//如果处于Doze状态,在power键灭屏时，首次会将wakefulness设置为该值} else if (wakefulness == WAKEFULNESS_DOZING) {if (isDreaming) {return; // continue dozing}//进入asleep状态reallyGoToSleepNoUpdateLocked(SystemClock.uptimeMillis(), Process.SYSTEM_UID);updatePowerStateLocked();}}//如果正处在Dream，则只要触发updatePowerStateLocked(),立即退出Dreamif (isDreaming) {mDreamManager.stopDream(false /*immediate*/);}...

说明：每次更新状态后都会重新调用updatePowerStateLocked，然后再次进入到handleSandman函数中。整个过程就是就是在条件合适后，这个方法中将启动屏保。

5 发送通知并更新 wakelock锁

5.1 发送通知 finishWakefulnessChangeLocked 分析

private void finishWakefulnessChangeLocked() {if (mWakefulnessChanging) {//通过Notifier进行wakefulness改变后的处理mNotifier.onWakefulnessChangeFinished(mWakefulness);mWakefulnessChanging = false;}
}

这里 Notifier好比PMS的一个喇叭，用来发送广播，和其他组件交互等。

5.2 更新wakelock锁 updateSuspendBlockerLocked 分析

private void updateSuspendBlockerLocked() {//根据是否有CPU的wakelock,来决定cpu是保持否唤醒final boolean needWakeLockSuspendBlocker = ((mWakeLockSummary & WAKE_LOCK_CPU) != 0);//根据前面屏幕相关的状态，来决定是否需要持有屏幕的锁final boolean needDisplaySuspendBlocker = needDisplaySuspendBlockerLocked();//屏幕如果不需要保持开启状态，那么可自动熄灭final boolean autoSuspend = !needDisplaySuspendBlocker;//应该是表示屏幕是否是可交互的final boolean interactive = mDisplayPowerRequest.isBrightOrDim();if (!autoSuspend && mDecoupleHalAutoSuspendModeFromDisplayConfig) {//通过native函数，调用底层的autosuspend_disablesetHalAutoSuspendModeLocked(false);}//在需要的情况下，获取CPU和屏幕的锁if (needWakeLockSuspendBlocker && !mHoldingWakeLockSuspendBlocker) {mWakeLockSuspendBlocker.acquire();mHoldingWakeLockSuspendBlocker = true;}if (needDisplaySuspendBlocker && !mHoldingDisplaySuspendBlocker) {mDisplaySuspendBlocker.acquire();mHoldingDisplaySuspendBlocker = true;}if (mDecoupleHalInteractiveModeFromDisplayConfig) {if (interactive || mDisplayReady) {//调用底层动态库的setInteractive函数，决定终端是否可以进行交互setHalInteractiveModeLocked(interactive);}}//如果不需要，则释放CPU和屏幕的锁 if (!needWakeLockSuspendBlocker && mHoldingWakeLockSuspendBlocker) {mWakeLockSuspendBlocker.release();mHoldingWakeLockSuspendBlocker = false;}if (!needDisplaySuspendBlocker && mHoldingDisplaySuspendBlocker) {mDisplaySuspendBlocker.release();mHoldingDisplaySuspendBlocker = false;}//如果需要设置自动休眠模式if (autoSuspend && mDecoupleHalAutoSuspendModeFromDisplayConfig) {setHalAutoSuspendModeLocked(true);}
}

这里 needDisplaySuspendBlockerLocked 方法决定屏幕是否关闭，代码实现如下：

private boolean needDisplaySuspendBlockerLocked() {if (!mDisplayReady) {//显示设备没准备好，不能关闭屏幕return true;}//如果屏幕开着/变暗if (mDisplayPowerRequest.isBrightOrDim()) {//距离传感器 没有工作，不能关闭屏幕if (!mDisplayPowerRequest.useProximitySensor || !mProximityPositive|| !mSuspendWhenScreenOffDueToProximityConfig) {return true;}}if (mScreenBrightnessBoostInProgress) {return true;}// Let the system suspend if the screen is off or dozing.return false; //可以关闭屏幕
}

needDisplaySuspendBlockerLocked主要根据屏幕的状态来决定，如果屏幕开着或处于变暗状态时，近距离传感器也没有工作，不能关闭屏幕。

通过本次源码分析，我们能看出仅管理当前的状态，涉及的细节就非常的琐碎。而屏幕和CPU的实际控制，还牵扯到大量其它对象和HAL层代码。 Android电源的管理实际上是基于Linux 电源管理策略的，因此若要真正掌握，还需要对Linux的电源管理策略作进一步的了解。