Android7.0 PowerManagerService(4) Power按键流程

按键的处理主要由InputManagerService负责，属于Android输入系统的流程。在这篇博客里，我们只关注与Power键相关的内容。InputManagerService处理的按键事件，最终将会传递到PhoneWindowManager的interceptKeyBeforeQueueing函数。
我们就从这个函数开始，逐步进行分析。

public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
    if (!mSystemBooted) {
        // If we have not yet booted, don't let key events do anything.
        return 0;
    }

    //表示屏幕是否点亮
    final boolean interactive = (policyFlags & FLAG_INTERACTIVE) != 0;
    final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
    final boolean canceled = event.isCanceled();
    //按键对应的编码
    final int keyCode = event.getKeyCode();
    .................
    switch (keyCode) {
        ...........
        case KeyEvent.KEYCODE_POWER: {
            result &= ~ACTION_PASS_TO_USER;
            isWakeKey = false; // wake-up will be handled separately
            if (down) {
                //处理按下Power键
                interceptPowerKeyDown(event, interactive);
            } else {
                //处理松开Power键
                interceptPowerKeyUp(event, interactive, canceled);
            }
             break;
        }
    }
    ..............
    if (isWakeKey) {
        //按power键时，isWakeKey置为false，于是不会调用wakeUp函数
        wakeUp(event.getEventTime(), mAllowTheaterModeWakeFromKey, "android.policy:KEY");
    }

    return result;
}

接下来，我们分别看一下interceptPowerKeyDown和interceptPowerKeyUp函数。

一、interceptPowerKeyDown

interceptPowerKeyDown用于处理按下Power键(还未松手释放)对应的事件。

private void interceptPowerKeyDown(KeyEvent event, boolean interactive) {
    // Hold a wake lock until the power key is released.
    // mPowerKeyWakeLock为PARTIAL_WAKE_LOCK级别的锁
    if (!mPowerKeyWakeLock.isHeld()) {
        //将调用到PMS的acquire WakeLock流程
        mPowerKeyWakeLock.acquire();
    }

    // Cancel multi-press detection timeout.
    //处理多次按power键的场景
    //每次power up时，发送MSG_POWER_DELAYED_PRESS的延迟消息
    //如果延迟消息被处理，说明一次完整的Power键处理结束（按下去，弹起来）
    //在延迟消息被处理前，再次按power键，就检测到多次点击了
    //实际上，原生终端不支持该场景
    if (mPowerKeyPressCounter != 0) {
        mHandler.removeMessages(MSG_POWER_DELAYED_PRESS);
    }

    // Detect user pressing the power button in panic when an application has
    // taken over the whole screen.
    // 从注释来看及mHiddenNavPanic的代码，觉得像是处理“误触”的
    boolean panic = mImmersiveModeConfirmation.onPowerKeyDown(interactive,
        SystemClock.elapsedRealtime(), isImmersiveMode(mLastSystemUiFlags));
    if (panic) {
        mHandler.post(mHiddenNavPanic);
    }

    // Latch power key state to detect screenshot chord.
    // 如果当前是亮屏状态，且满足触发截屏的条件，触发截屏功能
    if (interactive && !mScreenshotChordPowerKeyTriggered
            && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
        mScreenshotChordPowerKeyTriggered = true;
        mScreenshotChordPowerKeyTime = event.getDownTime();
        interceptScreenshotChord();
    }

    // Stop ringing or end call if configured to do so when power is pressed.
    TelecomManager telecomManager = getTelecommService();
    boolean hungUp = false;
    if (telecomManager != null) {
        if (telecomManager.isRinging()) {
            // Pressing Power while there's a ringing incoming
            // call should silence the ringer.
            //如果有电话拨入，且电话铃声响起，按Power键，设置电话响铃静音
            telecomManager.silenceRinger();
        } else if ((mIncallPowerBehavior
            & Settings.Secure.INCALL_POWER_BUTTON_BEHAVIOR_HANGUP) != 0
            && telecomManager.isInCall() && interactive) {
            // Otherwise, if "Power button ends call" is enabled,
            // the Power button will hang up any current active call.
            //如果正在接听电话，且配置了Power键挂断电话的话，按Power按键挂断正在接听的电话
            hungUp = telecomManager.endCall();
        }
    }

    GestureLauncherService gestureService = LocalServices.getService(
            GestureLauncherService.class);
    boolean gesturedServiceIntercepted = false;
    if (gestureService != null) {
        //手势对应的服务，尝试拦截处理Power键动作事件
        gesturedServiceIntercepted = gestureService.interceptPowerKeyDown(event, interactive,
                mTmpBoolean);
        if (mTmpBoolean.value && mGoingToSleep) {
            mCameraGestureTriggeredDuringGoingToSleep = true;
        }
    }

    // If the power key has still not yet been handled, then detect short
    // press, long press, or multi press and decide what to do.
    // Power键事件的处理，就像处理屏幕上的点击事件一样，也依赖于事件分发机制
    // 如果已经被消耗掉了，就不会再被继续处理
    mPowerKeyHandled = hungUp || mScreenshotChordVolumeDownKeyTriggered
            || mScreenshotChordVolumeUpKeyTriggered || gesturedServiceIntercepted;

    //Power键事件未被消耗掉
    if (!mPowerKeyHandled) {
        //屏幕还是亮的
        if (interactive) {
            // When interactive, we're already awake.
            // Wait for a long press or for the button to be released to decide what to do.
            //1、 判断是否支持长按的行为
            if (hasLongPressOnPowerBehavior()) {
                //2、 亮屏时，长按Power键将触发MSG_POWER_LONG_PRESS消息
                Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
                msg.setAsynchronous(true);
                mHandler.sendMessageDelayed(msg,
                        ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
            }
        } else {
            //此时屏幕是熄灭状态

            //3、先唤醒系统，这个会调用到PMS的wakeUp
            wakeUpFromPowerKey(event.getDownTime());

            //支持熄屏长按，mSupportLongPressPowerWhenNonInteractive读资源文件得到，默认为false
            if (mSupportLongPressPowerWhenNonInteractive && hasLongPressOnPowerBehavior()) {
                Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
                msg.setAsynchronous(true);
                mHandler.sendMessageDelayed(msg,
                        ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
                mBeganFromNonInteractive = true;
            } else {
                //默认返回1
                final int maxCount = getMaxMultiPressPowerCount();

                if (maxCount <= 1) {
                    //息屏时，按下power键（不弹起），仅消耗掉该事件
                    mPowerKeyHandled = true;
                } else {
                    mBeganFromNonInteractive = true;
                }
            }
        }
    }
}

1、hasLongPressOnPowerBehavior
hasLongPressOnPowerBehavior负责判断终端是否支持长按的行为：

private boolean hasLongPressOnPowerBehavior() {
    return getResolvedLongPressOnPowerBehavior() != LONG_PRESS_POWER_NOTHING;
}

private int getResolvedLongPressOnPowerBehavior() {
    //取决与系统属性"factory.long_press_power_off"，此处默认为false
    if (FactoryTest.isLongPressOnPowerOffEnabled()) {
        return LONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM;
    }

    return mLongPressOnPowerBehavior;
}

从上面的代码可以看出，终端是否支持长按行为，最终将由mLongPressOnPowerBehavior决定。

.........
mLongPressOnPowerBehavior = mContext.getResources().getInteger(
        com.android.internal.R.integer.config_longPressOnPowerBehavior);
.........

mLongPressOnPowerBehavior将在PhoneWindowManager初始化时，通过读取资源文件得到，一般情况下应该为1。
于是，hasLongPressOnPowerBehavior的值返回true，即终端支持Power键长按。

2、MSG_POWER_LONG_PRESS的处理
从上面的代码，我们知道亮屏时按Power键，会触发延迟的MSG_POWER_LONG_PRESS消息。
如果在MSG_POWER_LONG_PRESS超时前，Power键未被释放掉，那么此次操作被定义为长按Power键。

MSG_POWER_LONG_PRESS对应的处理函数为powerLongPress：

private void powerLongPress() {
    //也是由资源文件得到，默认为1，即LONG_PRESS_POWER_GLOBAL_ACTIONS
    final int behavior = getResolvedLongPressOnPowerBehavior();

    switch (behavior) {
        case LONG_PRESS_POWER_NOTHING:
            break;
        case LONG_PRESS_POWER_GLOBAL_ACTIONS:
            mPowerKeyHandled = true;
            //感觉这里是：终端对接收的事件处理后，给用户一个反馈信息
            //performHapticFeedbackLw主要进行震动反馈，例如按键后，终端震动一下
            //不同的事件，定义了不同的震动模式
            if (!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) {
                //如果没有震动反馈，这里尝试进行声音的反馈，例如响一下按键音
                performAuditoryFeedbackForAccessibilityIfNeed();
            }
            //弹出选择关机还是重启的对话框
            showGlobalActionsInternal();
            break;
        .........
    }
}

3、wakeUpFromPowerKey
在息屏的状态下按下Power键，将调用wakeUpFromPowerKey函数唤醒系统：

private void wakeUpFromPowerKey(long eventTime) {
    //从config.xml来看，mAllowTheaterModeWakeFromPowerKey默认为true
    wakeUp(eventTime, mAllowTheaterModeWakeFromPowerKey, "android.policy:POWER");
}

private boolean wakeUp(long wakeTime, boolean wakeInTheaterMode, String reason) {
    //取数据库的值
    final boolean theaterModeEnabled = isTheaterModeEnabled();
    //按Power键时，条件返回false
    if (!wakeInTheaterMode && theaterModeEnabled) {
        return false;
    }

    //看来唤醒时，将退出剧院模式
    if (theaterModeEnabled) {
        Settings.Global.putInt(mContext.getContentResolver(),
                Settings.Global.THEATER_MODE_ON, 0);
    }

    //最终将调用到PMS的wakeUp函数
    mPowerManager.wakeUp(wakeTime, reason);
    return true;
}

我们跟进一下PMS的wakeUp函数：

public void wakeUp(long eventTime, String reason, String opPackageName) {
    ..........
    try {
        wakeUpInternal(eventTime, reason, uid, opPackageName, uid);
    } finally {
        ...............
    }
}

private void wakeUpInternal(long eventTime, String reason, int uid, String opPackageName,
        int opUid) {
    synchronized (mLock) {
        //更新Wakefullness的状态为WAKEFULNESS_AWAKE，记录一次UserActivity
        if (wakeUpNoUpdateLocked(eventTime, reason, uid, opPackageName, opUid)) {
            //如之前博客所述，对整个电源状态进行一次调整，将在需要时点亮屏幕
            updatePowerStateLocked();
        }
    }
}

二、interceptPowerKeyUp
interceptPowerKeyUp处理松开Power键后的流程：

private void interceptPowerKeyUp(KeyEvent event, boolean interactive, boolean canceled) {
    //事件被取消，或者在按下Power键时，该事件已被消耗掉
    //那么就不用继续处理
    final boolean handled = canceled || mPowerKeyHandled;

    mScreenshotChordPowerKeyTriggered = false;
    //退出截屏
    cancelPendingScreenshotChordAction();
    //取消MSG_POWER_LONG_PRESS事件，即在一定事件内Power键弹起，则表示这一次不是长按Power键
    cancelPendingPowerKeyAction();

    //从之前的代码，我们知道除了特殊功能外
    //灭屏按Power键或亮屏长按时，均会消耗掉Power事件
    //因此，只有亮屏短按Power键需要进行处理
    if (!handled) {
        // Figure out how to handle the key now that it has been released.
        // 记录短按的次数
        mPowerKeyPressCounter += 1;

        final int maxCount = getMaxMultiPressPowerCount();
        final long eventTime = event.getDownTime();
        if (mPowerKeyPressCounter < maxCount) {
            // This could be a multi-press.  Wait a little bit longer to confirm.
            // Continue holding the wake lock.
            // 与之前interceptPowerKeyDown，处理Power键被多次按下场景对应
            // 每次被按下，均发送MSG_POWER_DELAYED_PRESS消息
            // 实际上maxCount为1，该不会进入该分支
            Message msg = mHandler.obtainMessage(MSG_POWER_DELAYED_PRESS,
                interactive ? 1 : 0, mPowerKeyPressCounter, eventTime);
            msg.setAsynchronous(true);
            mHandler.sendMessageDelayed(msg, ViewConfiguration.getDoubleTapTimeout());
            return;
        }

        //1、No other actions.  Handle it immediately.
        powerPress(eventTime, interactive, mPowerKeyPressCounter);
    }

    // 2、Done.  Reset our state.
    finishPowerKeyPress();
}

1、powerPress
我们跟进一下powerPress函数：

private void powerPress(long eventTime, boolean interactive, int count) {
    if (mScreenOnEarly && !mScreenOnFully) {
        Slog.i(TAG, "Suppressed redundant power key press while "
                + "already in the process of turning the screen on.");
        return;
    }

    if (count == 2) {
        //原生不进入
        powerMultiPressAction(eventTime, interactive, mDoublePressOnPowerBehavior);
    } else if (count == 3) {
        //原生不进入
        powerMultiPressAction(eventTime, interactive, mTriplePressOnPowerBehavior);
    } else if (interactive && !mBeganFromNonInteractive) {
        //亮屏时，将进入该分支

        //mShortPressOnPowerBehavior被配置为1
        switch (mShortPressOnPowerBehavior) {
            case SHORT_PRESS_POWER_NOTHING:
                break;
            case SHORT_PRESS_POWER_GO_TO_SLEEP:
                //最终调用到PMS的goToSleep函数
                mPowerManager.goToSleep(eventTime,
                        PowerManager.GO_TO_SLEEP_REASON_POWER_BUTTON, 0);
                break;
            ...............
        }
    }
}

从上面的代码可以看出，在亮屏状态下，短按一下Power键，最终将调用到PMS的goToSleep函数，使终端进入到休眠状态，与实际情况一致。
我们跟进一下PMS的goToSleep函数：

public void goToSleep(long eventTime, int reason, int flags) {
    ............
    try {
        goToSleepInternal(eventTime, reason, flags, uid);
    } finally {
        ...............
    }
}

private void goToSleepInternal(long eventTime, int reason, int flags, int uid) {
    synchronized (mLock) {
    //没有触发用户事件，将mWakefullness置为WAKEFULNESS_DOZING
    if (goToSleepNoUpdateLocked(eventTime, reason, flags, uid)) {
        //执行整体的电源状态更新，将熄灭屏幕
        updatePowerStateLocked();
    }
}

2、finishPowerKeyPress

每当处理一次完整的Power键按下、弹出操作后，interceptPowerKeyUp调用finishPowerKeyPress进行最后的状态复位操作：

private void finishPowerKeyPress() {
    mBeganFromNonInteractive = false;
    mPowerKeyPressCounter = 0;
    if (mPowerKeyWakeLock.isHeld()) {
        mPowerKeyWakeLock.release();
    }
}

从代码可以看出，主要的工作其实就是将状态变量恢复为初始值，同时释放掉最初申请的锁。

三、总结

整个Power按键的主要处理流程如上图所示。结合手机的实际情况，整个逻辑还是非常好理解的。