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