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。