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：

1. PARTIAL_WAKE_LOCK:保持CPU 运转，屏幕和键盘灯有可能是关闭的。

2. 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
3. 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
4. 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