二，关机流程
从前一篇博文我们知道，当用户长按Power键时会弹出（关机、重新启动，飞行模式等选项）对话框，我们点击关机，则会弹出关机确认对话框。那么从选项对话框到关机确认对话框又是一个什么流程呢。以下我们在简单分析一下：
showGlobalActionsDialog()-->showDialog()-->handleShow()-->createDialog()-->onPress()-->shutdown()
PhoneWindowManager.java
void showGlobalActionsDialog() {
......
mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned());
......
}
GlobalActions.java
public void showDialog(boolean keyguardShowing, boolean isDeviceProvisioned) {
......
handleShow();
......
}
private void handleShow() {
......
mDialog = createDialog();
......
}
private GlobalActionsDialog createDialog(){
......
mItems = new ArrayList<Action>();
// first: power off
mItems.add(
new SinglePressAction(
com.android.internal.R.drawable.uirom_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(true);
}
public boolean onLongPress() {
mWindowManagerFuncs.rebootSafeMode(true);
return true;
}
public boolean showDuringKeyguard() {
return true;
}
public boolean showBeforeProvisioning() {
return true;
}
});
......
}
上述代码中的mWindowManagerFuncs实际上是WindowManagerService的对象，该对象有PhoneWindowManager的init的方法传入GlobalActions的构造函数中，并在上述代码中进行调用。
以下这一行代码是调用的关键代码。
mPolicy.init(mContext, WindowManagerService.this, WindowManagerService.this);
以下是弹出“关机确认对话框”的堆栈：
01-16 18:08:21.497 D/bill ( 720): java.lang.Throwable
01-16 18:08:21.497 D/bill ( 720): at com.android.server.power.ShutdownThread.shutdown(ShutdownThread.java:175)
01-16 18:08:21.497 D/bill ( 720): at com.android.server.wm.WindowManagerService.shutdown(WindowManagerService.java:5783)01-16 18:08:21.497 D/bill ( 720):at com.android.internal.policy.impl.GlobalActions$2.onPress(GlobalActions.java:352)//WindowManagerService实现了接口WindowsManagerFuncs
01-16 18:08:21.497 D/bill ( 720): at com.android.internal.policy.impl.GlobalActions.onClick(GlobalActions.java:581)
01-16 18:08:21.497 D/bill ( 720): at com.android.internal.app.AlertController$AlertParams$3.onItemClick(AlertController.java:952)
01-16 18:08:21.497 D/bill ( 720): at android.widget.AdapterView.performItemClick(AdapterView.java:299)
01-16 18:08:21.497 D/bill ( 720): at android.widget.AbsListView.performItemClick(AbsListView.java:1152)
01-16 18:08:21.497 D/bill ( 720): at android.widget.AbsListView$PerformClick.run(AbsListView.java:3014)
01-16 18:08:21.497 D/bill ( 720): at android.widget.AbsListView$3.run(AbsListView.java:3865)
01-16 18:08:21.497 D/bill ( 720): at android.os.Handler.handleCallback(Handler.java:808)
01-16 18:08:21.497 D/bill ( 720): at android.os.Handler.dispatchMessage(Handler.java:103)
01-16 18:08:21.497 D/bill ( 720): at android.os.Looper.loop(Looper.java:193)
01-16 18:08:21.497 D/bill ( 720): at android.os.HandlerThread.run(HandlerThread.java:61)
从这里（shutdown()）我们正式进入关机流程的关键。
shutdown()<ShutdownThread.java> --->shutdownInner() --->beginShutdownSequence（）--->run()--->rebootOrShutdown()--->lowLevelShutdown()<PowerManagerService.java>--->
源代码来自：https://github.com/android/platform_frameworks_base/blob/master/services/java/com/android/server/power/ShutdownThread.java
public static void shutdown(final Context context, boolean confirm) {
mReboot = false;
mRebootSafeMode = false;
shutdownInner(context, confirm);
}
注！
參数2：confir;关机操作前是否须要用户进行确认
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);
//longPressBehavior的值标示当前长按Power操作意向（关机、重新启动。
。。）
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);
if (confirm) {
final CloseDialogReceiver closer = new CloseDialogReceiver(context);
if (sConfirmDialog != null) {
sConfirmDialog.dismiss();
}
sConfirmDialog = 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 = sConfirmDialog;
sConfirmDialog.setOnDismissListener(closer);
sConfirmDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
sConfirmDialog.show();
} else {
beginShutdownSequence(context);
}
}
注：上述代码中，假设须要用户确认关机操作，则会弹出对话框。在对话框的确认button被触发时，调用beginShutdownSequence（）方法继续关机流程。假设无需用户确认，则直接调用beginShutdownSequence（）进入下一个关机流程节点。
在beginShutdownSequence（）有些手机厂商经常会在这里加入一些定制功能，比如在对话框中加入“下次高速开机”。定制关机动画等等。
随后会依据不同平台进行解说。以下这张图是Android原生系统的关机画面（相应以下加粗显示的代码）：
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();
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");①
sInstance.mCpuWakeLock.setReferenceCounted(false);②
sInstance.mCpuWakeLock.acquire(); ③
} 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;④
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() {
};
sInstance.start();⑤
}
注解！
①上述红色代码中的作用主要是为了防止手机进入休眠状态。从代码中我们看到。此时通过PowerManager的newWakeLock方法生成了PowerManager.WakeLock对象。newWakeLock（）是PowerManager中最为经常使用的方法，该对象是一种锁机制，通过该对象能够控制设备的电源状态。在生成WakeLock实例时通过第一个參数的传入仅仅开控制获取不同的WakeLock，主要是不同的lock对CPU，屏幕，键盘灯有不同的影响。例如以下：
- PARTIAL_WAKE_LOCK:保持CPU 运转，屏幕和键盘灯有可能是关闭的。
- SCREEN_DIM_WAKE_LOCK：保持CPU 运转。同意保持屏幕显示但有可能是灰的。同意关闭键盘灯
- SCREEN_BRIGHT_WAKE_LOCK：保持CPU 运转。同意保持屏幕高亮显示。同意关闭键盘灯
- FULL_WAKE_LOCK：保持CPU 运转，保持屏幕高亮显示，键盘灯也保持亮度
②Wake Lock 是一种锁的机制。仅仅要有人拿着这个锁，系统九五案发进入休眠，能够被用户动态程序和内核获得，这个锁能够使有超时的或者是没有超时的。超时的锁会在时间过去以后自己主动解锁。假设没有锁了，或者超时了。内核就会启动休眠的那套机制来进入休眠。PowerManager.WakeLock有加锁和解锁的两种状态。加锁的方式有两种。一种是永久的锁住，这样的锁除非是显示的放开，否则是不会解锁的。所以这样的锁用起来要很小心，另外一种锁是超时锁，这样的锁会在锁住一段时间后自己主动解锁。
sInstance.mCpuWakeLock.setReferenceCounted(false);是设置锁的方式为永久的锁住。
③sInstance.mCpuWakeLock.acquire(); 加锁
④上述蓝色代码的作用是为了保证用户体验，保持屏幕、键盘的亮度
⑤接着启动关机线程，进入关机流程的下一个节点。
/**
* Makes sure we handle the shutdown gracefully.
* Shuts off power regardless of radio and bluetooth state if the alloted time has passed.
*/
public void run() {
BroadcastReceiver br = new BroadcastReceiver() {
@Override public void onReceive(Context context, Intent intent) {
actionDone();//这里用于接受关机广播，actionDone（）方法主要是防止应用程序取消关机操作。
}
};
/*
* Write a system property in case the system_server reboots before we
* get to the actual hardware restart. If that happens, we‘ll retry at
* the beginning of the SystemServer startup.
*/
{
String reason = (mReboot ? "1" : "0") + (mRebootReason != null ? mRebootReason : "");
SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
}
/*
* If we are rebooting into safe mode, write a system property
* indicating so.
*/
if (mRebootSafeMode) {
SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
}
Log.i(TAG, "Sending shutdown broadcast...");
// First send the high-level shut down broadcast.
mActionDone = false;
Intent intent = new Intent(Intent.ACTION_SHUTDOWN);
intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND);
mContext.sendOrderedBroadcastAsUser(intent,
UserHandle.ALL, null, br, mHandler, 0, null, null);//发送关机广播
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) {
}
}
}
Log.i(TAG, "Shutting down activity manager...");
final IActivityManager am =
ActivityManagerNative.asInterface(ServiceManager.checkService("activity"));
if (am != null) {
try {
am.shutdown(MAX_BROADCAST_TIME);//关闭ActivityManagerService
} catch (RemoteException e) {
}
}
Log.i(TAG, "Shutting down package manager...");
final PackageManagerService pm = (PackageManagerService)
ServiceManager.getService("package");
if (pm != null) {
pm.shutdown();//关闭PackageManagerService服务
}
// 关闭Radios
shutdownRadios(MAX_RADIO_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");
// Set initial variables and time out time.
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);//关闭MountService
} 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) {
}
}
}
rebootOrShutdown(mReboot, mRebootReason);
}
最后调用rebootOrShutdown（）
public static void rebootOrShutdown(boolean reboot, String reason) {
if (reboot) {
Log.i(TAG, "Rebooting, reason: " + reason);
PowerManagerService.lowLevelReboot(reason);
Log.e(TAG, "Reboot failed, will attempt shutdown instead");
} else if (SHUTDOWN_VIBRATE_MS > 0) {
// vibrate before shutting down
Vibrator vibrator = new SystemVibrator();
try {
vibrator.vibrate(SHUTDOWN_VIBRATE_MS);//关机震动
} 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) {
}
}
// Shutdown power
Log.i(TAG, "Performing low-level shutdown...");
PowerManagerService.lowLevelShutdown();//关闭电源
}
}
/**
* Low-level function turn the device off immediately, without trying
* to be clean. Most people should use {@link ShutdownThread} for a clean shutdown.
*/
public static void lowLevelShutdown() {
SystemProperties.set("sys.powerctl", "shutdown");//这里通过改动Android属性进行关机
}
注：上述代码中，红色加粗部分为关机关键代码。我也能够通过adb 命令进行改动Android系统的属性进行关机，详细命令例如以下
adb shell setprop sys.powerctl shutdown