Android电源管理系列之PowerManagerService(二)
WakeLock机制 PowerManager.WakeLock 为了延长电池的使用寿命，Android设备会在一段时间后使屏幕变暗，然后关闭屏幕显示，直至停止CPU进入休眠。WakeLock是Android提供的唤醒锁机制，用来保持CPU运行或避免屏幕变暗/关闭以及避免键盘背光灯熄灭 唤醒锁的类型： Flag CPU Screen Keyboard PARTIAL_WAKE_LOCK on off off SCREEN_DIM_WAKE_LOCK on Dim off SCREEN_BRIGHT_WAKE_LOCK on Bright off FULL_WAKE_LOCK on Bright on 如果是PARTIAL_WAKE_LOCK,无论屏幕的状态或是按下电源键, CPU都将正常工作。如果是其它的唤醒锁,设备会在用户按下电源钮后停止工作进入休眠状态。以上四种锁，除了PARTIAL_WAKE_LOCK，其余的锁在API level 17已经被deprecated了。 唤醒锁的使用方法 代码使用： PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE); PowerManager.WakeLock wl = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "My Tag"); wl.acquire(); //acquire时尽量申明timeout时间// ... do work...wl.release(); 权限申明： <uses-permission android:name="android.permission.WAKE_LOCK" /><uses-permission android:name="android.permission.DEVICE_POWER"/> 在应用程序中使用WakeLock时必须申明权限，acquire请求唤醒锁时尽量设置timeout时间释放WakeLock，以避免长时间持有WakeLock导致系统无法休眠。 唤醒锁的实现：frameworks/base/core/java/android/os/PowerManager.java public final class WakeLock { private int mFlags; private String mTag; private final String mPackageName; private final IBinder mToken; private int mCount; private boolean mRefCounted = true; private boolean mHeld; private WorkSource mWorkSource; private String mHistoryTag; private final String mTraceName; ...... WakeLock(int flags, String tag, String packageName) { mFlags = flags; mTag = tag; mPackageName = packageName; mToken = new Binder(); mTraceName = "WakeLock (" + mTag + ")"; } ...... } updatePowerStateLocked frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java protected void updatePowerStateLocked() { // 服务没有ready,mDirty值没有设置情况下不做更新操作 if (!mSystemReady || mDirty == 0) { return; } if (!Thread.holdsLock(mLock)) { Slog.wtf(TAG, "Power manager lock was not held when calling updatePowerStateLocked"); } try { // Phase 0: 更新基本状态 updateIsPoweredLocked(mDirty); updateStayOnLocked(mDirty); updateScreenBrightnessBoostLocked(mDirty); // Phase 1: Update wakefulness. // Loop because the wake lock and user activity computations are influenced // by changes in wakefulness. final long now = SystemClock.uptimeMillis(); int dirtyPhase2 = 0; for (;;) { int dirtyPhase1 = mDirty; dirtyPhase2 |= dirtyPhase1; mDirty = 0; updateWakeLockSummaryLocked(dirtyPhase1); updateUserActivitySummaryLocked(now, dirtyPhase1); if (!updateWakefulnessLocked(dirtyPhase1)) { break; } } // Phase 2: Update display power state. boolean displayBecameReady = updateDisplayPowerStateLocked(dirtyPhase2); // Phase 3: Update dream state (depends on display ready signal). updateDreamLocked(dirtyPhase2, displayBecameReady); // Phase 4: Send notifications, if needed. finishWakefulnessChangeIfNeededLocked(); // Phase 5: Update suspend blocker. // Because we might release the last suspend blocker here, we need to make sure // we finished everything else first! updateSuspendBlockerLocked(); } finally { Trace.traceEnd(Trace.TRACE_TAG_POWER); } } 首先来看updateIsPoweredLocked(mDirty); private void updateIsPoweredLocked(int dirty) { if ((dirty & DIRTY_BATTERY_STATE) != 0) { final boolean wasPowered = mIsPowered; final int oldPlugType = mPlugType; final boolean oldLevelLow = mBatteryLevelLow; mIsPowered = mBatteryManagerInternal.isPowered(BatteryManager.BATTERY_PLUGGED_ANY); mPlugType = mBatteryManagerInternal.getPlugType(); mBatteryLevel = mBatteryManagerInternal.getBatteryLevel(); mBatteryLevelLow = mBatteryManagerInternal.getBatteryLevelLow(); if (wasPowered != mIsPowered || oldPlugType != mPlugType) { mDirty |= DIRTY_IS_POWERED; // Update wireless dock detection state. final boolean dockedOnWirelessCharger = mWirelessChargerDetector.update( mIsPowered, mPlugType, mBatteryLevel); // Treat plugging and unplugging the devices as a user activity. // Users find it disconcerting when they plug or unplug the device // and it shuts off right away. // Some devices also wake the device when plugged or unplugged because // they don't have a charging LED. final long now = SystemClock.uptimeMillis(); if (shouldWakeUpWhenPluggedOrUnpluggedLocked(wasPowered, oldPlugType, dockedOnWirelessCharger)) { wakeUpNoUpdateLocked(now, "android.server.power:POWER", Process.SYSTEM_UID, mContext.getOpPackageName(), Process.SYSTEM_UID); } userActivityNoUpdateLocked( now, PowerManager.USER_ACTIVITY_EVENT_OTHER, 0, Process.SYSTEM_UID); // Tell the notifier whether wireless charging has started so that // it can provide feedback to the user. //Bug293654, zhanghong.wt, modify, 20170914, modify no notificatin ring while plugging USB if (dockedOnWirelessCharger || (mIsPowered && oldPlugType != mPlugType&&("1".equals(SystemProperties.get("sys.boot_completed"))))) { mNotifier.onWirelessChargingStarted(); } } if (wasPowered != mIsPowered || oldLevelLow != mBatteryLevelLow) { if (oldLevelLow != mBatteryLevelLow && !mBatteryLevelLow) { if (DEBUG_SPEW) { Slog.d(TAG, "updateIsPoweredLocked: resetting low power snooze"); } mAutoLowPowerModeSnoozing = false; } updateLowPowerModeLocked(); } } } 最后附上PowerManagerService 总结图
