updatePowerStateLocked

/**
     * Updates the global power state based on dirty bits recorded in mDirty.
     *
     * This is the main function that performs power state transitions.
     * We centralize them here so that we can recompute the power state completely
     * each time something important changes, and ensure that we do it the same
     * way each time.  The point is to gather all of the transition logic here.
     */
    private void updatePowerStateLocked() {
        if (!mSystemReady || mDirty == 0) {
            return;
        }
        if (!Thread.holdsLock(mLock)) {
            Slog.wtf(TAG, "Power manager lock was not held when calling updatePowerStateLocked");
        }

        Trace.traceBegin(Trace.TRACE_TAG_POWER, "updatePowerState");
        try {
            // Phase 0: Basic state updates.
            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);
        }
    }
 

updateIsPoweredLocked

/**
     * Updates the value of mIsPowered.
     * Sets DIRTY_IS_POWERED if a change occurred.
     */
    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);//從BatteryService獲取
            mPlugType = mBatteryManagerInternal.getPlugType();
            mBatteryLevel = mBatteryManagerInternal.getBatteryLevel();
            mBatteryLevelLow = mBatteryManagerInternal.getBatteryLevelLow();

            if (DEBUG_SPEW) {
                Slog.d(TAG, "updateIsPoweredLocked: wasPowered=" + wasPowered
                        + ", mIsPowered=" + mIsPowered
                        + ", oldPlugType=" + oldPlugType
                        + ", mPlugType=" + mPlugType
                        + ", mBatteryLevel=" + mBatteryLevel);
            }

            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)) {//是否需要喚醒裝置
                    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.
                if (dockedOnWirelessCharger) {
                    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();//更新低功耗模式
            }
        }
    }
 

首先systemReady函式會把mDirty置位為DIRTY_BATTERY_STATE，還有收BatterySevice發出來的廣播，也會置這個標誌位

    private final class BatteryReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            synchronized (mLock) {
                handleBatteryStateChangedLocked();
            }
        }
    }
 

    private void handleBatteryStateChangedLocked() {
        mDirty |= DIRTY_BATTERY_STATE;
        updatePowerStateLocked();
    }

shouldWakeUpWhenPluggedOrUnpluggedLocked

private boolean shouldWakeUpWhenPluggedOrUnpluggedLocked(
            boolean wasPowered, int oldPlugType, boolean dockedOnWirelessCharger) {
        // Don't wake when powered unless configured to do so.
        if (!mWakeUpWhenPluggedOrUnpluggedConfig) {
            return false;
        }

        // Don't wake when undocked from wireless charger.
        // See WirelessChargerDetector for justification.
        if (wasPowered && !mIsPowered
                && oldPlugType == BatteryManager.BATTERY_PLUGGED_WIRELESS) {
            return false;
        }

        // Don't wake when docked on wireless charger unless we are certain of it.
        // See WirelessChargerDetector for justification.
        if (!wasPowered && mIsPowered
                && mPlugType == BatteryManager.BATTERY_PLUGGED_WIRELESS
                && !dockedOnWirelessCharger) {
            return false;
        }

        // If already dreaming and becoming powered, then don't wake.
        if (mIsPowered && mWakefulness == WAKEFULNESS_DREAMING) {
            return false;
        }

        // Don't wake while theater mode is enabled.
        if (mTheaterModeEnabled && !mWakeUpWhenPluggedOrUnpluggedInTheaterModeConfig) {
            return false;
        }

        // Otherwise wake up!
        return true;
    }

updateStayOnLocked

繼續分析updatePowerStateLocked函式，分析updateStayOnLocked函式。一般這個函式mStatyon為fasle，除非在資源中設定哪種充電狀態下可以長亮。

/**
     * Updates the value of mStayOn.
     * Sets DIRTY_STAY_ON if a change occurred.
     */
    private void updateStayOnLocked(int dirty) {
        if ((dirty & (DIRTY_BATTERY_STATE | DIRTY_SETTINGS)) != 0) {//當dirty是電池狀態和設定的狀態改變時
            final boolean wasStayOn = mStayOn;
            if (mStayOnWhilePluggedInSetting != 0 //這個值從資源中讀取，一般設定的話代表哪種充電時可以常亮
                    && !isMaximumScreenOffTimeoutFromDeviceAdminEnforcedLocked()) {//看有沒有設mMaximumScreenOffTimeoutFromDeviceAdmin螢幕最大亮屏時間，沒設預設最大。那麼這個函式返回是false
                mStayOn = mBatteryManagerInternal.isPowered(mStayOnWhilePluggedInSetting);
            } else {
                mStayOn = false;
            }

            if (mStayOn != wasStayOn) {
                mDirty |= DIRTY_STAY_ON;
            }
        }
    }

updateScreenBrightnessBoostLocked

這個函式是更新螢幕是否保持最亮狀態

private void updateScreenBrightnessBoostLocked(int dirty) {
//這個狀態實在boostScreenBrightnessInternal函式中設定最亮時置位，當然下面傳送訊息MSG_SCREEN_BRIGHTNESS_BOOST_TIMEOUT也會將這個標誌位置位
 if ((dirty & DIRTY_SCREEN_BRIGHTNESS_BOOST) != 0) {
            if (mScreenBrightnessBoostInProgress) {//當前正在最亮螢幕這個狀態
                final long now = SystemClock.uptimeMillis();
                mHandler.removeMessages(MSG_SCREEN_BRIGHTNESS_BOOST_TIMEOUT);
                if (mLastScreenBrightnessBoostTime > mLastSleepTime) {
                    final long boostTimeout = mLastScreenBrightnessBoostTime +
                            SCREEN_BRIGHTNESS_BOOST_TIMEOUT;
                    if (boostTimeout > now) {//看當前時間是否小於最亮螢幕結束的時間
                        Message msg = mHandler.obtainMessage(MSG_SCREEN_BRIGHTNESS_BOOST_TIMEOUT);
                        msg.setAsynchronous(true);
                        mHandler.sendMessageAtTime(msg, boostTimeout);//傳送一個延遲的訊息，到最亮螢幕結束的時候接受到訊息，將標誌位置為DIRTY_SCREEN_BRIGHTNESS_BOOST後，重新再回到這個函式
                        return;
                    }
                }
                mScreenBrightnessBoostInProgress = false;
                mNotifier.onScreenBrightnessBoostChanged();
                userActivityNoUpdateLocked(now,
                        PowerManager.USER_ACTIVITY_EVENT_OTHER, 0, Process.SYSTEM_UID);
            }
        }
    }

接下來看updatePowerStateLocked函式的另一個階段,

// 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;//這個迴圈中每次新的mDirty全部給dirtyPhase1，並且在這個迴圈中使用這個dirty
                dirtyPhase2 |= dirtyPhase1;//dirtyPhase2 會把之前所有的mDirty狀態全部或上，然後用這個狀態繼續下面的函式
                mDirty = 0;

                updateWakeLockSummaryLocked(dirtyPhase1);
                updateUserActivitySummaryLocked(now, dirtyPhase1);
                if (!updateWakefulnessLocked(dirtyPhase1)) {
                    break;
                }
            }

updateWakeLockSummaryLocked

/**
     * Updates the value of mWakeLockSummary to summarize the state of all active wake locks.
     * Note that most wake-locks are ignored when the system is asleep.
     *
     * This function must have no other side-effects.
     */
    @SuppressWarnings("deprecation")
    private void updateWakeLockSummaryLocked(int dirty) {
        if ((dirty & (DIRTY_WAKE_LOCKS | DIRTY_WAKEFULNESS)) != 0) {
            mWakeLockSummary = 0;

            final int numWakeLocks = mWakeLocks.size();
            for (int i = 0; i < numWakeLocks; i++) {
                final WakeLock wakeLock = mWakeLocks.get(i);
                switch (wakeLock.mFlags & PowerManager.WAKE_LOCK_LEVEL_MASK) {
                    case PowerManager.PARTIAL_WAKE_LOCK:
                        if (!wakeLock.mDisabled) {
                            // We only respect this if the wake lock is not disabled.
                            mWakeLockSummary |= WAKE_LOCK_CPU;
                        }
                        break;
                    case PowerManager.FULL_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_SCREEN_BRIGHT | WAKE_LOCK_BUTTON_BRIGHT;
                        break;
                    case PowerManager.SCREEN_BRIGHT_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_SCREEN_BRIGHT;
                        break;
                    case PowerManager.SCREEN_DIM_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_SCREEN_DIM;
                        break;
                    case PowerManager.PROXIMITY_SCREEN_OFF_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_PROXIMITY_SCREEN_OFF;
                        break;
                    case PowerManager.DOZE_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_DOZE;
                        break;
                    case PowerManager.DRAW_WAKE_LOCK:
                        mWakeLockSummary |= WAKE_LOCK_DRAW;
                        break;
                }
            }

            // Cancel wake locks that make no sense based on the current state.
            if (mWakefulness != WAKEFULNESS_DOZING) {
                mWakeLockSummary &= ~(WAKE_LOCK_DOZE | WAKE_LOCK_DRAW);//下面根據各種狀態，將上面或上的mWakeLockSummary，減去
            }
            if (mWakefulness == WAKEFULNESS_ASLEEP
                    || (mWakeLockSummary & WAKE_LOCK_DOZE) != 0) {
                mWakeLockSummary &= ~(WAKE_LOCK_SCREEN_BRIGHT | WAKE_LOCK_SCREEN_DIM
                        | WAKE_LOCK_BUTTON_BRIGHT);
                if (mWakefulness == WAKEFULNESS_ASLEEP) {
                    mWakeLockSummary &= ~WAKE_LOCK_PROXIMITY_SCREEN_OFF;
                }
            }

            // Infer implied wake locks where necessary based on the current state.
            if ((mWakeLockSummary & (WAKE_LOCK_SCREEN_BRIGHT | WAKE_LOCK_SCREEN_DIM)) != 0) {//只要有螢幕鎖，cpu鎖必須持有
                if (mWakefulness == WAKEFULNESS_AWAKE) {
                    mWakeLockSummary |= WAKE_LOCK_CPU | WAKE_LOCK_STAY_AWAKE;
                } else if (mWakefulness == WAKEFULNESS_DREAMING) {
                    mWakeLockSummary |= WAKE_LOCK_CPU;
                }
            }
            if ((mWakeLockSummary & WAKE_LOCK_DRAW) != 0) {
                mWakeLockSummary |= WAKE_LOCK_CPU;
            }

            if (DEBUG_SPEW) {
                Slog.d(TAG, "updateWakeLockSummaryLocked: mWakefulness="
                        + PowerManagerInternal.wakefulnessToString(mWakefulness)
                        + ", mWakeLockSummary=0x" + Integer.toHexString(mWakeLockSummary));
            }
        }
    }

updateUserActivitySummaryLocked

 /**
     * Updates the value of mUserActivitySummary to summarize the user requested
     * state of the system such as whether the screen should be bright or dim.
     * Note that user activity is ignored when the system is asleep.
     *
     * This function must have no other side-effects.
     */
    private void updateUserActivitySummaryLocked(long now, int dirty) {
        // Update the status of the user activity timeout timer.
        if ((dirty & (DIRTY_WAKE_LOCKS | DIRTY_USER_ACTIVITY
                | DIRTY_WAKEFULNESS | DIRTY_SETTINGS)) != 0) {
            mHandler.removeMessages(MSG_USER_ACTIVITY_TIMEOUT);

            long nextTimeout = 0;
            if (mWakefulness == WAKEFULNESS_AWAKE
                    || mWakefulness == WAKEFULNESS_DREAMING
                    || mWakefulness == WAKEFULNESS_DOZING) {
                final int sleepTimeout = getSleepTimeoutLocked();
                final int screenOffTimeout = getScreenOffTimeoutLocked(sleepTimeout);
                final int screenDimDuration = getScreenDimDurationLocked(screenOffTimeout);

                mUserActivitySummary = 0;
                if (mLastUserActivityTime >= mLastWakeTime) {//userActivity的time大於上次喚醒時間
                    nextTimeout = mLastUserActivityTime
                            + screenOffTimeout - screenDimDuration;
                    if (now < nextTimeout) {
                        mUserActivitySummary = USER_ACTIVITY_SCREEN_BRIGHT;
                    } else {
                        nextTimeout = mLastUserActivityTime + screenOffTimeout;
                        if (now < nextTimeout) {
                            mUserActivitySummary = USER_ACTIVITY_SCREEN_DIM;
                        }
                    }
                }
                if (mUserActivitySummary == 0
                        && mLastUserActivityTimeNoChangeLights >= mLastWakeTime) {
                    nextTimeout = mLastUserActivityTimeNoChangeLights + screenOffTimeout;
                    if (now < nextTimeout) {
                        if (mDisplayPowerRequest.policy == DisplayPowerRequest.POLICY_BRIGHT) {
                            mUserActivitySummary = USER_ACTIVITY_SCREEN_BRIGHT;
                        } else if (mDisplayPowerRequest.policy == DisplayPowerRequest.POLICY_DIM) {
                            mUserActivitySummary = USER_ACTIVITY_SCREEN_DIM;
                        }
                    }
                }
                if (mUserActivitySummary == 0) {
                    if (sleepTimeout >= 0) {
                        final long anyUserActivity = Math.max(mLastUserActivityTime,
                                mLastUserActivityTimeNoChangeLights);
                        if (anyUserActivity >= mLastWakeTime) {
                            nextTimeout = anyUserActivity + sleepTimeout;
                            if (now < nextTimeout) {
                                mUserActivitySummary = USER_ACTIVITY_SCREEN_DREAM;
                            }
                        }
                    } else {
                        mUserActivitySummary = USER_ACTIVITY_SCREEN_DREAM;
                        nextTimeout = -1;//該值為-1，下面就不會發送訊息了
                    }
                }
                if (mUserActivitySummary != 0 && nextTimeout >= 0) {
                    Message msg = mHandler.obtainMessage(MSG_USER_ACTIVITY_TIMEOUT);
                    msg.setAsynchronous(true);
                    mHandler.sendMessageAtTime(msg, nextTimeout);
                }
            } else {
                mUserActivitySummary = 0;
            }

            if (DEBUG_SPEW) {
                Slog.d(TAG, "updateUserActivitySummaryLocked: mWakefulness="
                        + PowerManagerInternal.wakefulnessToString(mWakefulness)
                        + ", mUserActivitySummary=0x" + Integer.toHexString(mUserActivitySummary)
                        + ", nextTimeout=" + TimeUtils.formatUptime(nextTimeout));
            }
        }
    }

MSG_USER_ACTIVITY_TIMEOUT的訊息處理

    /**
     * Handler for asynchronous operations performed by the power manager.
     */
    private final class PowerManagerHandler extends Handler {
        public PowerManagerHandler(Looper looper) {
            super(looper, null, true /*async*/);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_USER_ACTIVITY_TIMEOUT:
                    handleUserActivityTimeout();
                    break;
                case MSG_SANDMAN:
                    handleSandman();
                    break;
                case MSG_SCREEN_BRIGHTNESS_BOOST_TIMEOUT:
                    handleScreenBrightnessBoostTimeout();
                    break;
            }
        }
    }

updateWakefulnessLocked

 /**
     * Updates the wakefulness of the device.
     *
     * This is the function that decides whether the device should start dreaming
     * based on the current wake locks and user activity state.  It may modify mDirty
     * if the wakefulness changes.
     *
     * Returns true if the wakefulness changed and we need to restart power state calculation.
     */
    private boolean updateWakefulnessLocked(int dirty) {
        boolean changed = false;
        if ((dirty & (DIRTY_WAKE_LOCKS | DIRTY_USER_ACTIVITY | DIRTY_BOOT_COMPLETED
                | DIRTY_WAKEFULNESS | DIRTY_STAY_ON | DIRTY_PROXIMITY_POSITIVE
                | DIRTY_DOCK_STATE)) != 0) {
            if (mWakefulness == WAKEFULNESS_AWAKE && isItBedTimeYetLocked()) {
                if (DEBUG_SPEW) {
                    Slog.d(TAG, "updateWakefulnessLocked: Bed time...");
                }
                final long time = SystemClock.uptimeMillis();
                if (shouldNapAtBedTimeLocked()) {
                    changed = napNoUpdateLocked(time, Process.SYSTEM_UID);
                } else {
                    changed = goToSleepNoUpdateLocked(time,
                            PowerManager.GO_TO_SLEEP_REASON_TIMEOUT, 0, Process.SYSTEM_UID);
                }
            }
        }
        return changed;
    }

再來看看isItBedTimeYetLocked函式，isBeingKeptAwakeLocked函式，如果isBeingKeptAwakeLocked返回true代表處於亮屏狀態，isItBedTimeYetLocked返回false，上面的for死迴圈退出

/**
     * Returns true if the device is being kept awake by a wake lock, user activity
     * or the stay on while powered setting.  We also keep the phone awake when
     * the proximity sensor returns a positive result so that the device does not
     * lock while in a phone call.  This function only controls whether the device
     * will go to sleep or dream which is independent of whether it will be allowed
     * to suspend.
     */
    private boolean isBeingKeptAwakeLocked() {
        return mStayOn
                || mProximityPositive
                || (mWakeLockSummary & WAKE_LOCK_STAY_AWAKE) != 0
                || (mUserActivitySummary & (USER_ACTIVITY_SCREEN_BRIGHT
                        | USER_ACTIVITY_SCREEN_DIM)) != 0
                || mScreenBrightnessBoostInProgress;
    }

如果isBeingKeptAwakeLocked返回false，並且mBootCompleted 為true開機完成了。那麼updateWakefulnessLocked函式進入判斷條件
那再來看看shouldNapAtBedTimeLocked函式，就是看有沒有做夢這個設定，如果沒有直接到goToSleepNoUpdateLocked函式，到了goToSleepNoUpdateLocked函式後將mWakefulness 設為WAKEFULNESS_DOZING顯示返回true還要繼續迴圈，下次到updateWakefulnessLocked這個函式，不是awake型別的，也返回false，直接退出死迴圈了。到napNoUpdateLocked函式也是一樣的先是將mWakefulness置為WAKEFULNESS_DREAMING，返回true，繼續迴圈，下次不是awake型別就返回false，退出迴圈了。

    /**
     * Returns true if the device should automatically nap and start dreaming when the user
     * activity timeout has expired and it's bedtime.
     */
    private boolean shouldNapAtBedTimeLocked() {
        return mDreamsActivateOnSleepSetting
                || (mDreamsActivateOnDockSetting
                        && mDockState != Intent.EXTRA_DOCK_STATE_UNDOCKED);
    }

下篇部落格繼續分析updatePowerStateLocked中的

            // Phase 2: Update display power state.
            boolean displayBecameReady = updateDisplayPowerStateLocked(dirtyPhase2);