Android关机流程解析---从reboot说起

Android关机流程解析

在PowerManager的API文档中，给出了一个关机/重启接口：

public void reboot (String reason)
对于这个接口的描述很简单，就是几句话。

接口的作用就是重启设备，而且，就算重启成功了也没有返回值。

需要包含REBOOT权限，也就是android.permission.REBOOT

唯一参数reason代表需要的特定重启模式，比如recovery，当然也可以为null。

--------------------------------上层空间--------------------------------

1.frameworks/base/core/java/android/os/PowerManager.java

[java]
* Reboot the device. Will not return if the reboot is
* successful. Requires the {@link android.Manifest.permission#REBOOT}
* permission.
*
* @param reason code to pass to the kernel (e.g., "recovery") to
*               request special boot modes, or null.
*/
public void reboot(String reason)
{
    try {
        mService.reboot(reason);
    } catch (RemoteException e) {
    }
}

    public void reboot(String reason)
    {
        try {
            mService.reboot(reason);
        } catch (RemoteException e) {
        }
    }
mService为IPowerManager Binder接口服务。

[java]

public PowerManager(IPowerManager service, Handler handler)
{
mService = service;
mHandler = handler;
}

    public PowerManager(IPowerManager service, Handler handler)
    {
        mService = service;
        mHandler = handler;
    }

2.frameworks/base/core/java/android/os/IPowerManager.aidl

[java]
interface IPowerManager
{
...
void reboot(String reason);
...
}

interface IPowerManager
{
...
void reboot(String reason);
...
}

3.frameworks/base/services/java/com/android/server/PowerManagerService.java

[java]

public void reboot(String reason)
{
    mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);

    if (mHandler == null || !ActivityManagerNative.isSystemReady()) {
        throw new IllegalStateException("Too early to call reboot()");
    }

    final String finalReason = reason;
    Runnable runnable = new Runnable() {
        public void run() {
            synchronized (this) {
                ShutdownThread.reboot(getUiContext(), finalReason, false);
            }

        }
    };
    // ShutdownThread must run on a looper capable of displaying the UI.
    mHandler.post(runnable);

    // PowerManager.reboot() is documented not to return so just wait for the inevitable.
    synchronized (runnable) {
        while (true) {
            try {
                runnable.wait();
            } catch (InterruptedException e) {
            }
        }
    }
}

    public void reboot(String reason)
    {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);

        if (mHandler == null || !ActivityManagerNative.isSystemReady()) {
            throw new IllegalStateException("Too early to call reboot()");
        }

        final String finalReason = reason;
        Runnable runnable = new Runnable() {
            public void run() {
                synchronized (this) {
                    ShutdownThread.reboot(getUiContext(), finalReason, false);
                }

            }
        };
        // ShutdownThread must run on a looper capable of displaying the UI.
        mHandler.post(runnable);

        // PowerManager.reboot() is documented not to return so just wait for the inevitable.
        synchronized (runnable) {
            while (true) {
                try {
                    runnable.wait();
                } catch (InterruptedException e) {
                }
            }
        }
    }

4.frameworks/base/services/java/com/android/server/pm/ShutdownThread.java

[java]

public static void reboot(final Context context, String reason, boolean confirm) {
    mReboot = true;
    mRebootSafeMode = false;
    mRebootReason = reason;
    shutdownInner(context, confirm);
}

    public static void reboot(final Context context, String reason, boolean confirm) {
        mReboot = true;
        mRebootSafeMode = false;
        mRebootReason = reason;
        shutdownInner(context, confirm);
    }
这里说明是需要重启，且不是安全模式，重启参数为传递下来的reason，shutdownInner的confirm参数是用来设置是否有确认提示框的，通过reboot接口调用重启是没有的，为false。

重启的实现在run()中，因为ShutdownThread是Thread的扩展，所以run会自动运行。

[java]

public void run() {
    BroadcastReceiver br = new BroadcastReceiver() {
        @Override public void onReceive(Context context, Intent intent) {
            // We don't allow apps to cancel this, so ignore the result.
            actionDone();
        }
    };


    {
        String reason = (mReboot ? "1" : "0") + (mRebootReason != null ? mRebootReason : "");
        SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
    }


    if (mRebootSafeMode) {
        SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
    }
    ...
    rebootOrShutdown(mReboot, mRebootReason);
}

    public void run() {
        BroadcastReceiver br = new BroadcastReceiver() {
            @Override public void onReceive(Context context, Intent intent) {
                // We don't allow apps to cancel this, so ignore the result.
                actionDone();
            }
        };

        {
            String reason = (mReboot ? "1" : "0") + (mRebootReason != null ? mRebootReason : "");
            SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
        }

        if (mRebootSafeMode) {
            SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
        }
        ...
        rebootOrShutdown(mReboot, mRebootReason);
    }

在重启前会将重启原因写入sys.shutdown.requested，如果没有则为空，如果是安全模式还会将persist.sys.safemode置1，之后会进行一些关机前的预处理，关闭ActivityManager以及MountService，最终调用rebootOrShutdown进行关机操作。

[java]

    public static void rebootOrShutdown(boolean reboot, String reason) {
        if (reboot) {
            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) {
            // vibrate before shutting down
            Vibrator vibrator = new SystemVibrator();
            try {
                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.

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