Android关机流程源码分析

上一篇文章Android 开关机动画显示源码分析详细介绍了开关机动画的显示过程，Android系统开机时，在启动SurfaceFlinger服务过程中通过Android属性系统方式来启动bootanim进程，实现开机动画显示过程；当系统关机时，又是如何启动关机动画的呢？Android系统的整个关机流程又是怎样的呢？本文就针对这两个问题透过源码来给出具体的分析。我们知道，当长按电源键，系统会弹出关机提示对话框

当点击选择关机时，系统就会完成整个关机流程。接下来就通过源码来介绍Android关机流程的完整实现过程。当长按电源键时，按键消息被分发到PhoneWindowManager的interceptKeyBeforeQueueing函数中处理：

public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags, boolean isScreenOn) {
    ...
    switch (keyCode) {
        ...
        case KeyEvent.KEYCODE_POWER: {
            result &= ~ACTION_PASS_TO_USER;
            if (down) {
                if (isScreenOn && !mPowerKeyTriggered
                        && (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
                    mPowerKeyTriggered = true;
                    mPowerKeyTime = event.getDownTime();
                    interceptScreenshotChord();//抓屏
                }
                ITelephony telephonyService = getTelephonyService();
                boolean hungUp = false;
                if (telephonyService != null) {
                    try {
                        if (telephonyService.isRinging()) {
                            //当来电时按下电源键，启动静音
                            telephonyService.silenceRinger();
                        } else if ((mIncallPowerBehavior
                                & Settings.Secure.INCALL_POWER_BUTTON_BEHAVIOR_HANGUP) != 0
                                && telephonyService.isOffhook()) {
                            // Otherwise, if "Power button ends call" is enabled,
                            // the Power button will hang up any current active call.
                            hungUp = telephonyService.endCall();
                        }
                    } catch (RemoteException ex) {
                        Log.w(TAG, "ITelephony threw RemoteException", ex);
                    }
                }
                interceptPowerKeyDown(!isScreenOn || hungUp
                        || mVolumeDownKeyTriggered || mVolumeUpKeyTriggered);
            } else {
                ...
            }
            break;
        }
        ...
    }
    return result;
}

电源键和音量键的组合可以实现特定功能，比如按下电源键和音量向下键，可实现抓屏，interceptKeyBeforeQueueing函数首先根据条件处理电源键按下的特定任务，然后调用interceptPowerKeyDown做进一步处理

private void interceptPowerKeyDown(boolean handled) {
    mPowerKeyHandled = handled;
    if (!handled) {
        //隔500ms处理电源按键事件
        mHandler.postDelayed(mPowerLongPress, ViewConfiguration.getGlobalActionKeyTimeout());
    }
}

这里的mHandler是在初始化PhoneWindowManager对象时创建的

public void init(Context context, IWindowManager windowManager,WindowManagerFuncs windowManagerFuncs,
        LocalPowerManager powerManager) {
    ...
    mHandler = new PolicyHandler();
    ...
}

将一个Runnable对象mPowerLongPress发送到PolicyHandler中进行处理

private final Runnable mPowerLongPress = new Runnable() {
    public void run() {
        // The context isn't read
        if (mLongPressOnPowerBehavior < 0) {
            mLongPressOnPowerBehavior = mContext.getResources().getInteger(
                    com.android.internal.R.integer.config_longPressOnPowerBehavior);
        }
        switch (mLongPressOnPowerBehavior) {
        case LONG_PRESS_POWER_NOTHING:
            break;
        case LONG_PRESS_POWER_GLOBAL_ACTIONS:
            mPowerKeyHandled = true;
            performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false);
            sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
            showGlobalActionsDialog();
            break;
        case LONG_PRESS_POWER_SHUT_OFF:
            mPowerKeyHandled = true;
            performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false);
            sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
            mWindowManagerFuncs.shutdown();
            break;
        }
    }
};

在处理电源长按事件时，根据mLongPressOnPowerBehavior完成不同的处理过程，mLongPressOnPowerBehavior的值是通过配置文件来设置的，在frameworks/base/core/res/values/config.xml中有以下一段配置：

通过读取配置文件取得config_longPressOnPowerBehavior配置的值为1，因此将显示关机对话框

case LONG_PRESS_POWER_GLOBAL_ACTIONS:
    mPowerKeyHandled = true;
    performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false);
    //向ActivityManagerService请求关闭所有窗口
    sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
    //显示关机对话框
    showGlobalActionsDialog();
    break;

关机对话框显示：

void showGlobalActionsDialog() {
    //创建GlobalActions对象
    if (mGlobalActions == null) {
        mGlobalActions = new GlobalActions(mContext, mWindowManagerFuncs);
    }
    final boolean keyguardShowing = keyguardIsShowingTq();
    //显示对话框
    mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned());
    if (keyguardShowing) {
        // since it took two seconds of long press to bring this up,
        // poke the wake lock so they have some time to see the dialog.
        mKeyguardMediator.pokeWakelock();
    }
}

通过GlobalActions的showDialog函数来显示对话框

public void showDialog(boolean keyguardShowing, boolean isDeviceProvisioned) {
    mKeyguardShowing = keyguardShowing;
    mDeviceProvisioned = isDeviceProvisioned;
    if (mDialog != null) {
        mDialog.dismiss();
        mDialog = null;
        // Show delayed, so that the dismiss of the previous dialog completes
        mHandler.sendEmptyMessage(MESSAGE_SHOW);
    } else {
        handleShow();//关机对话框显示
    }
}

private void handleShow() {
    //创建对话框
    mDialog = createDialog();
    prepareDialog();//设置对话框属性
    mDialog.show();//显示对话框
    mDialog.getWindow().getDecorView().setSystemUiVisibility(View.STATUS_BAR_DISABLE_EXPAND);
}

createDialog()函数用于创建一个即将显示的关机对话框，就是前面图片显示的对话框。

private AlertDialog createDialog() {
    //=========================创建对话框显示的列表项视图=====================================
    //每一个列表项被被抽象为Action对象，
    // Simple toggle style if there's no vibrator, otherwise use a tri-state
    if (!mHasVibrator) {
        mSilentModeAction = new SilentModeToggleAction();
    } else {
        mSilentModeAction = new SilentModeTriStateAction(mContext, mAudioManager, mHandler);
    }
    //创建飞行模式切换ToggleAction对象
    mAirplaneModeOn = new ToggleAction(
            R.drawable.ic_lock_airplane_mode,
            R.drawable.ic_lock_airplane_mode_off,
            R.string.global_actions_toggle_airplane_mode,
            R.string.global_actions_airplane_mode_on_status,
            R.string.global_actions_airplane_mode_off_status) {
        void onToggle(boolean on) {
            if (mHasTelephony && Boolean.parseBoolean(SystemProperties.get(TelephonyProperties.PROPERTY_INECM_MODE))) {
                mIsWaitingForEcmExit = true;
                // Launch ECM exit dialog
                Intent ecmDialogIntent =new Intent(TelephonyIntents.ACTION_SHOW_NOTICE_ECM_BLOCK_OTHERS, null);
                ecmDialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                mContext.startActivity(ecmDialogIntent);
            } else {
                changeAirplaneModeSystemSetting(on);
                mHandler.removeMessages(EVENT_SERVICE_CHANGE_WAIT_TIMEOUT);
                mHandler.sendEmptyMessageDelayed(EVENT_SERVICE_CHANGE_WAIT_TIMEOUT,DELAY_AIRPLANE_SET_TIME);
            }
        }
        @Override
        protected void changeStateFromPress(boolean buttonOn) {
            if (!mHasTelephony) return;
            // In ECM mode airplane state cannot be changed
            if (!(Boolean.parseBoolean(SystemProperties.get(TelephonyProperties.PROPERTY_INECM_MODE)))) {
                mState = buttonOn ? State.TurningOn : State.TurningOff;
                mAirplaneState = mState;
            }
        }
        public boolean showDuringKeyguard() {
            return true;
        }
        public boolean showBeforeProvisioning() {
            return false;
        }
    };
    //更新当前飞行模式状态
    onAirplaneModeChanged();
    onRadioBusyStateChanged();
    mItems = new ArrayList<Action>();
    //向mItems列表中依次添加关机选择，飞行模式切换，静音模式选择
    // first: power off
    mItems.add(
        //创建关机SinglePressAction
        new SinglePressAction(com.android.internal.R.drawable.ic_lock_power_off,
                R.string.global_action_power_off) {
            public void onPress() {
                // shutdown by making sure radio and power are handled accordingly.
                mWindowManagerFuncs.shutdown();
            }
            public boolean onLongPress() {
                mWindowManagerFuncs.rebootSafeMode();
                return true;
            }
            public boolean showDuringKeyguard() {
                return true;
            }
            public boolean showBeforeProvisioning() {
                return true;
            }
        });
    // next: airplane mode
    mItems.add(mAirplaneModeOn);
    // last: silent mode
    if (SHOW_SILENT_TOGGLE) {
        mItems.add(mSilentModeAction);
    }
    //获取系统中所有用户信息
    List<UserInfo> users = mContext.getPackageManager().getUsers();
    if (users.size() > 1) {//对于多用户Android系统，在显示的对话框下面添加用户切换选项
        UserInfo currentUser;
        try {
            currentUser = ActivityManagerNative.getDefault().getCurrentUser();
        } catch (RemoteException re) {
            currentUser = null;
        }
        for (final UserInfo user : users) {
            boolean isCurrentUser = currentUser == null
                    ? user.id == 0 : (currentUser.id == user.id);
            SinglePressAction switchToUser = new SinglePressAction(
                    com.android.internal.R.drawable.ic_menu_cc,
                    (user.name != null ? user.name : "Primary")
                    + (isCurrentUser ? " u2714" : "")) {
                public void onPress() {
                    try {
                        ActivityManagerNative.getDefault().switchUser(user.id);
                        getWindowManager().lockNow();
                    } catch (RemoteException re) {
                        Log.e(TAG, "Couldn't switch user " + re);
                    }
                }

                public boolean showDuringKeyguard() {
                    return true;
                }

                public boolean showBeforeProvisioning() {
                    return false;
                }
            };
            mItems.add(switchToUser);
        }
    }
    mAdapter = new MyAdapter();//创建适配器，保存了所有数据，这里用MyAdapter保存列表项视图
    //=========================创建对话框=========================================
    final AlertDialog.Builder ab = new AlertDialog.Builder(mContext);
    ab.setAdapter(mAdapter, this).setInverseBackgroundForced(true);
    final AlertDialog dialog = ab.create();
    dialog.getListView().setItemsCanFocus(true);
    dialog.getListView().setLongClickable(true);
    dialog.getListView().setOnItemLongClickListener(
            new AdapterView.OnItemLongClickListener() {
                @Override
                public boolean onItemLongClick(AdapterView<?> parent, View view, int position,
                        long id) {
                    return mAdapter.getItem(position).onLongPress();//视图和数据相关联
                }
    });
    dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_DIALOG);
    dialog.setOnDismissListener(this);
    return dialog;
}

这里需要介绍对话框列表创建的方法，代码实现比较灵魂，值得学习。首先将显示对话框列表中的每一项用应该Action来描述，Action是一个接口，定义了每一个列表项的动作方法

各个列表项定义不同类型的Action，比如关机选项使用SinglePressAction来描述，目前Android系统定义了几种类型的Action，对应关机对话框中的不同选项。

将创建的列表选项添加到动态数组mItems中，并且为该对话框定义一个适配器MyAdapter，在单击对话框列表项时，调用适配器中对应的项来响应单击事件。Android适配器的使用实现了MVC编程模式，将数据和视图分开。通常我们将数据保存在一个数组中，通过适配器和视图控件关联显示，只不过这里的数据比较特殊，它是用来描述列表项显示的内容。

public boolean onItemLongClick(AdapterView<?> parent, View view, int position,long id) {
    return mAdapter.getItem(position).onLongPress();
}

public void onClick(DialogInterface dialog, int which) {
    if (!(mAdapter.getItem(which) instanceof SilentModeTriStateAction)) {
        dialog.dismiss();
    }
    mAdapter.getItem(which).onPress();
}

对于关机选项，其单击和长按事件处理过程如下：

public void onPress() {
    // shutdown by making sure radio and power are handled accordingly.
    mWindowManagerFuncs.shutdown();
}

public boolean onLongPress() {
    mWindowManagerFuncs.rebootSafeMode();
    return true;
}

对关机的处理都是调用mWindowManagerFuncs来完成的，mWindowManagerFuncs的类型为WindowManagerFuncs，在调用PhoneWindowManager的init函数时通过参数传进来。mWindowManagerFuncs对象在那里构造呢？WindowManagerService定义了一个WindowManagerPolicy类型变量：

final WindowManagerPolicy mPolicy = PolicyManager.makeNewWindowManager();

通过策略管理类PolicyManager对象的makeNewWindowManager函数创建一个窗口策略管理对象

public static WindowManagerPolicy makeNewWindowManager() {
    return sPolicy.makeNewWindowManager();
}

该函数通过Binder通信方式请求服务端Policy来完成对象的创建过程

Policy.java

public WindowManagerPolicy makeNewWindowManager() {
    return new PhoneWindowManager();
}

在WindowManagerService的构造过程中，会创建一个PolicyThread类来初始化窗口管理策略WindowManagerPolicy

private WindowManagerService(Context context, PowerManagerService pm,
        boolean haveInputMethods, boolean showBootMsgs, boolean onlyCore) {
    ...
    PolicyThread thr = new PolicyThread(mPolicy, this, context, pm);
    thr.start();
    synchronized (thr) {
        while (!thr.mRunning) {
            try {
                thr.wait();
            } catch (InterruptedException e) {
            }
        }
    }
    ...
}

在PolicyThread线程中执行初始化函数

static class PolicyThread extends Thread {
    @Override
    public void run() {
        Looper.prepare();
        ...
        mPolicy.init(mContext, mService, mService, mPM);
        synchronized (this) {
            mRunning = true;
            notifyAll();
        }
        ...
        Looper.loop();
    }
}

mPolicy的类型定义为WindowManagerPolicy类型，而WindowManagerPolicy是一个接口类型，PhoneWindowManager实现了该接口，为mPolicy创建的真正对象是PhoneWindowManager对象，因此PolicyThread线程将调用PhoneWindowManager的init函数

public void init(Context context, IWindowManager windowManager,
        WindowManagerFuncs windowManagerFuncs,LocalPowerManager powerManager) {
    ...
    mWindowManagerFuncs = windowManagerFuncs;
    ...
}

传进来的参数windowManager和windowManagerFuncs都是WindowManagerService对象，因为WindowManagerService继承于IWindowManager.Stub类同时实现了WindowManagerPolicy.WindowManagerFuncs接口，这下就很清晰地知道GlobalActions类中的mWindowManagerFuncs变量其实是WindowManagerService对象，因此关机的单击及长按事件由WindowManagerService实现：

public void shutdown() {
    ShutdownThread.shutdown(mContext, true);
}

public void rebootSafeMode() {
    ShutdownThread.rebootSafeMode(mContext, true);
}

WindowManagerService也不真正实现关机操作，而是转交个ShutdownThread来完成。对于关机处理过程：

public static void shutdown(final Context context, boolean confirm) {
    mReboot = false;
    mRebootSafeMode = false;
    shutdownInner(context, confirm);
}

该函数实现非常简单，只是设置一些标志位，然后将关机任务又转交给shutdownInner来处理，这里的参数confirm用于标识是否需要弹出关机确认对话框。

static void shutdownInner(final Context context, boolean confirm) {
    // ensure that only one thread is trying to power down.
    // any additional calls are just returned
    synchronized (sIsStartedGuard) {
        if (sIsStarted) {
            Log.d(TAG, "Request to shutdown already running, returning.");
            return;
        }
    }
    final int longPressBehavior = context.getResources().getInteger(
                    com.android.internal.R.integer.config_longPressOnPowerBehavior);
    final int resourceId = mRebootSafeMode
            ? com.android.internal.R.string.reboot_safemode_confirm
            : (longPressBehavior == 2
                    ? com.android.internal.R.string.shutdown_confirm_question
                    : com.android.internal.R.string.shutdown_confirm);
    Log.d(TAG, "Notifying thread to start shutdown longPressBehavior=" + longPressBehavior);
    //显示关机确认对话框
    if (confirm) {
        final CloseDialogReceiver closer = new CloseDialogReceiver(context);
        final AlertDialog dialog = new AlertDialog.Builder(context)
                .setTitle(mRebootSafeMode
                        ? com.android.internal.R.string.reboot_safemode_title
                        : com.android.internal.R.string.power_off)
                .setMessage(resourceId)
                .setPositiveButton(com.android.internal.R.string.yes, new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        beginShutdownSequence(context);
                    }
                })
                .setNegativeButton(com.android.internal.R.string.no, null)
                .create();
        closer.dialog = dialog;
        dialog.setOnDismissListener(closer);
        dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
        dialog.show();
    } else {//不显示关机确认对话框，直接进入关机流程
        beginShutdownSequence(context);
    }
}

调用beginShutdownSequence函数进入关机流程。

private static void beginShutdownSequence(Context context) {
    synchronized (sIsStartedGuard) {
        if (sIsStarted) {
            Log.d(TAG, "Shutdown sequence already running, returning.");
            return;
        }
        sIsStarted = true;
    }
    // throw up an indeterminate system dialog to indicate radio is
    // shutting down.
    ProgressDialog pd = new ProgressDialog(context);
    pd.setTitle(context.getText(com.android.internal.R.string.power_off));
    pd.setMessage(context.getText(com.android.internal.R.string.shutdown_progress));
    pd.setIndeterminate(true);
    pd.setCancelable(false);
    pd.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
    //pd.show();
    shutdownTime = SystemClock.elapsedRealtime() + MAX_SHUTDOWN_TIME;
    //执行关机动画
    String[] bootcmd = {"bootanimation", "shutdown"} ;
    try {
        Log.i(TAG, "exec the bootanimation ");
        SystemProperties.set("service.bootanim.exit", "0");
        Runtime.getRuntime().exec(bootcmd);
    } catch (Exception e){
       Log.e(TAG,"bootanimation command exe err!");
    }
    //初始化关机线程ShutdownThread
    sInstance.mContext = context;
    sInstance.mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
    // make sure we never fall asleep again
    sInstance.mCpuWakeLock = null;
    try {
        sInstance.mCpuWakeLock = sInstance.mPowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG + "-cpu");
        sInstance.mCpuWakeLock.setReferenceCounted(false);
        sInstance.mCpuWakeLock.acquire();
    } catch (SecurityException e) {
        Log.w(TAG, "No permission to acquire wake lock", e);
        sInstance.mCpuWakeLock = null;
    }
    // also make sure the screen stays on for better user experience
    sInstance.mScreenWakeLock = null;
    if (sInstance.mPowerManager.isScreenOn()) {
        try {
            sInstance.mScreenWakeLock = sInstance.mPowerManager.newWakeLock(
                    PowerManager.FULL_WAKE_LOCK, TAG + "-screen");
            sInstance.mScreenWakeLock.setReferenceCounted(false);
            sInstance.mScreenWakeLock.acquire();
        } catch (SecurityException e) {
            Log.w(TAG, "No permission to acquire wake lock", e);
            sInstance.mScreenWakeLock = null;
        }
    }
    // start the thread that initiates shutdown
    sInstance.mHandler = new Handler() {
    };
    //启动关机线程ShutdownThread
    sInstance.start();
}

这个函数执行两个任务，1）通过虚拟机Runtime启动关机动画进程bootanimation，用于显示关机动画，开关机动画在Android 开关机动画显示源码分析进行了详细的分析介绍。2）启动关机线程ShutdownThread来完成关机操作

public void run() {
    BroadcastReceiver br = new BroadcastReceiver() {
        @Override public void onReceive(Context context, Intent intent) {
            // 用于接收关机广播
            actionDone();
        }
    };
    //写属性"sys.shutdown.requested"保存关机原因
    {
        String reason = (mReboot ? "1" : "0") + (mRebootReason != null ? mRebootReason : "");
        SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
    }
    //如果是安全模式关机，写属性"persist.sys.safemode"
    if (mRebootSafeMode) {
        SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
    }
    Log.i(TAG, "Sending shutdown broadcast...");
    // First send the high-level shut down broadcast.
    mActionDone = false;
    //发送关机广播
    mContext.sendOrderedBroadcast(new Intent(Intent.ACTION_SHUTDOWN), null,
            br, mHandler, 0, null, null);
    //等待10S，前面定义的广播接收器收到关机广播时mActionDone设置为true，同时取消等待
    final long endTime = SystemClock.elapsedRealtime() + MAX_BROADCAST_TIME;
    synchronized (mActionDoneSync) {
        while (!mActionDone) {
            long delay = endTime - SystemClock.elapsedRealtime();
            if (delay <= 0) {
                Log.w(TAG, "Shutdown broadcast timed out");
                break;
            }
            try {
                mActionDoneSync.wait(delay);
            } catch (InterruptedException e) {
            }
        }
    }
    //10S时间内关闭ActivityManager服务
    final IActivityManager am =ActivityManagerNative.asInterface(ServiceManager.checkService("activity"));
    if (am != null) {
        try {
            am.shutdown(MAX_BROADCAST_TIME);
        } catch (RemoteException e) {
        }
    }
    //12s内关闭radios.
    shutdownRadios(MAX_RADIO_WAIT_TIME);
    //10s内关闭ICCS
    shutdownIccs(MAX_ICC_WAIT_TIME);
    // Shutdown MountService to ensure media is in a safe state
    IMountShutdownObserver observer = new IMountShutdownObserver.Stub() {
        public void onShutDownComplete(int statusCode) throws RemoteException {
            Log.w(TAG, "Result code " + statusCode + " from MountService.shutdown");
            actionDone();
        }
    };
    Log.i(TAG, "Shutting down MountService");
    //20s内关闭MountService服务
    mActionDone = false;
    final long endShutTime = SystemClock.elapsedRealtime() + MAX_SHUTDOWN_WAIT_TIME;
    synchronized (mActionDoneSync) {
        try {
            final IMountService mount = IMountService.Stub.asInterface(ServiceManager.checkService("mount"));
            if (mount != null) {
                mount.shutdown(observer);
            } else {
                Log.w(TAG, "MountService unavailable for shutdown");
            }
        } catch (Exception e) {
            Log.e(TAG, "Exception during MountService shutdown", e);
        }
        while (!mActionDone) {
            long delay = endShutTime - SystemClock.elapsedRealtime();
            if (delay <= 0) {
                Log.w(TAG, "Shutdown wait timed out");
                break;
            }
            try {
                mActionDoneSync.wait(delay);
            } catch (InterruptedException e) {
            }
        }
    }
    //关机时间定义为5s，这里计算关机超过的时间
    long shutdownDelay = shutdownTime - SystemClock.elapsedRealtime();
    if (shutdownDelay > 0) {
        Log.i(TAG, "Shutdown delay:"+shutdownDelay);
        SystemClock.sleep(shutdownDelay);
    }
    //继续关机
    rebootOrShutdown(mReboot, mRebootReason);
}

该函数内主要完成以下一些工作：

(1)发送关机广播ACTION_SHUTDOWN

(2)关闭ActivityManager 服务

(3)关闭无线相关的服务

(4)关闭Iccs

(5)关闭MountService服务

public static void rebootOrShutdown(boolean reboot, String reason) {
    if (reboot) {//是否重启
        Log.i(TAG, "Rebooting, reason: " + reason);
        try {
            PowerManagerService.lowLevelReboot(reason);
        } catch (Exception e) {
            Log.e(TAG, "Reboot failed, will attempt shutdown instead", e);
        }
    } else if (SHUTDOWN_VIBRATE_MS > 0) {//震动时间为500ms
        // vibrate before shutting down
        Vibrator vibrator = new SystemVibrator();
        try {
            //关机震动500ms
            vibrator.vibrate(SHUTDOWN_VIBRATE_MS);
        } catch (Exception e) {
            // Failure to vibrate shouldn't interrupt shutdown.  Just log it.
            Log.w(TAG, "Failed to vibrate during shutdown.", e);
        }
        // vibrator is asynchronous so we need to wait to avoid shutting down too soon.
        try {
            Thread.sleep(SHUTDOWN_VIBRATE_MS);
        } catch (InterruptedException unused) {
        }
    }
    //关闭电源
    Log.i(TAG, "Performing low-level shutdown...");
    PowerManagerService.lowLevelShutdown();
}

这里是启动关机震动并关闭电源

public static void lowLevelShutdown() {
    nativeShutdown();
}

这里通过JNI调用C++的关机函数

static void nativeShutdown(JNIEnv *env, jobject clazz) {
    delFlag();
    android_reboot(ANDROID_RB_POWEROFF, 0, 0);
}

android_reboot函数最终通过Linux系统调用关闭系统。到此关机操作就基本完成了。