Android关机流程

今天研究学习了Android的关机流程。

大家都知道，当长按power按键时，手机就会弹出一个对话框，从对话框中我们可以选择“关机”选项。此功能是在PhoneWindowManager.java中实现完成（frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java），在此文件中有interceptKeyBeforeQueueing方法用于接收按键事件，然后对各个不同的事件做出相应的操作，其中power按键的操作如下：

public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags, boolean isScreenOn) {    ......    switch (keyCode) {......case KeyEvent.KEYCODE_POWER: {    if ((mTopFullscreenOpaqueWindowState.getAttrs().flags & WindowManager.LayoutParams.PREVENT_POWER_KEY) != 0){    return result;    }    result &= ~ACTION_PASS_TO_USER;    if (down) { // 如果是按下键if (isScreenOn && !mPowerKeyTriggered&& (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {    mPowerKeyTriggered = true; // 按键触发为true    mPowerKeyTime = event.getDownTime(); // 记录事件时间    cancelPendingRingerChordAction(); // 结束音量长按事件    interceptScreenshotChord(); // 判断是否是截屏处理}// 当电话铃响起时，则会静音，而正在通话时，则会挂掉电话ITelephony telephonyService = getTelephonyService();boolean hungUp = false;if (telephonyService != null) {    try {        if (telephonyService.isRinging()) {    // Pressing Power while there's a ringing incoming    // call should silence the ringer.    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);    }        }// 延迟固定时间触发长按事件，长按事件主要是弹出全局对话框  interceptPowerKeyDown(!isScreenOn || hungUp                            || mVolumeDownKeyTriggered || mVolumeUpKeyTriggered);    } else {mPowerKeyTriggered = false;cancelPendingScreenshotChordAction();if (interceptPowerKeyUp(canceled || mPendingPowerKeyUpCanceled)) {    result = (result & ~ACTION_POKE_USER_ACTIVITY) | ACTION_GO_TO_SLEEP;}mPendingPowerKeyUpCanceled = false;    }    break;}......    }}

在interceptKeyBeforeQueueing方法中主要使用interceptPowerKeyDown方法来触发长按事件。

private void interceptPowerKeyDown(boolean handled) {    mPowerKeyHandled = handled;    if (!handled) {mHandler.postDelayed(mPowerLongPress, ViewConfiguration.getGlobalActionKeyTimeout());    }}private final Runnable mPowerLongPress = new Runnable() {    public void run() {// The context isn't readif (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);                ShutdownThread.shutdown(mContext, true);                break;        }    }};

在interceptPowerKeyDown方法中，通过postDelayed使得mPowerLongPress延时一段时间执行，而在mPowerLongPress中，则通过showGlobalActionsDialog方法来弹出全局对话框。

void showGlobalActionsDialog() {    if (mGlobalActions == null) {mGlobalActions = new GlobalActions(mContext);    }    final boolean keyguardShowing = mKeyguardMediator.isShowingAndNotHidden();    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();    }}

其中mGlobalActions是GlobalActions类型的对象（frameworks/base/policy/src/com/android/internal/policy/impl/GlobalActions.java），其showDialog实现如下所示

public void showDialog(boolean keyguardShowing, boolean isDeviceProvisioned) {    mKeyguardShowing = keyguardShowing;    mDeviceProvisioned = isDeviceProvisioned;    if (mDialog != null && mUiContext == null) {mDialog.dismiss();mDialog = null;    }    if (mDialog == null) {mDialog = createDialog();    }    prepareDialog();    mDialog.show();    mDialog.getWindow().getDecorView().setSystemUiVisibility(View.STATUS_BAR_DISABLE_EXPAND);}

此方法将mDialog显示出来，而mDialog是使用createDialog来创建的。

private AlertDialog createDialog() {    ......    mItems = new ArrayList<Action>();    // first: power off    mItems.add(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.ShutdownThread.shutdown(getUiContext(), true);    }    public boolean showDuringKeyguard() {return true;    }    public boolean showBeforeProvisioning() {return true;    }});    ......    return dialog;}

方法createDialog用于创建全局对话框中的各个选项，其中包括关机选项，当选择关机选项时会使用ShutdownThread类中的shutdown方法来执行关机（frameworks/base/core/java/com/android/internal/app/ShutdownThread.java）。

public static void shutdown(final Context context, boolean confirm) {    ......    if (confirm) {final AlertDialog dialog;// Set different dialog message based on whether or not we're rebootingif (mReboot) {            ......    } else {    dialog = new AlertDialog.Builder(context)    .setIconAttribute(android.R.attr.alertDialogIcon)    .setTitle(com.android.internal.R.string.power_off)    .setMessage(com.android.internal.R.string.shutdown_confirm)    .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();}dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);dialog.show();    } else {beginShutdownSequence(context);    }}

方法shutdown主要是用来弹出一个确认对话框，如果点击确认了会再使用beginShutdownSequence来执行关机。

private static void beginShutdownSequence(Context context) {    ......    // start the thread that initiates shutdown    sInstance.mHandler = new Handler() {    };    sInstance.start();}public void run() {    ......    rebootOrShutdown(mReboot, mRebootReason);}public static void rebootOrShutdown(boolean reboot, String reason) {    ......    // Shutdown power    Log.i(TAG, "Performing low-level shutdown...");    Power.shutdown();}

在beginShutdownSequence方法中会启动一个线程来执行关机，而sInstance就是ShutdownThread类型的对象，当其start时会调用run函数，而在run函数中会使用rebootOrShutdown，最终会调用Power类中的shutdown来执行关机操作（frameworks/base/core/java/os/Power.java）。而在Power类中会调用android_os_Power.cpp（frameworks/base/core/jni/android_os_Power.cpp）中的jni方法android_os_Power_shutdown。

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

在android_os_Power_shutdown会调用android_reboot，而android_reboot的实现是在/system/core/libcutils/android_reboot.c中，在android_reboot中还会调用reboot方法，此方法实现于/bionic/libc/unistd/reboot.c中。

int android_reboot(int cmd, int flags, char *arg){    ......    switch (cmd) {        case ANDROID_RB_RESTART:            reason = RB_AUTOBOOT;            break;        case ANDROID_RB_POWEROFF:            ret = reboot(RB_POWER_OFF);            return ret;        case ANDROID_RB_RESTART2:            // REBOOT_MAGIC            break;        default:            return -1;    }    ......    return ret;}int reboot (int  mode) {    return __reboot( LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL );}

而__reboot方法使用汇编语言传递这些参数至kernel，在kernel/kernel/sys.c中有实现

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,void __user *, arg){    char buffer[256];    int ret = 0;    ......    /* For safety, we require "magic" arguments. */    if (magic1 != LINUX_REBOOT_MAGIC1 ||    (magic2 != LINUX_REBOOT_MAGIC2 &&    magic2 != LINUX_REBOOT_MAGIC2A &&    magic2 != LINUX_REBOOT_MAGIC2B &&    magic2 != LINUX_REBOOT_MAGIC2C))return -EINVAL;    /* Instead of trying to make the power_off code look like    * halt when pm_power_off is not set do it the easy way.    */    if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)cmd = LINUX_REBOOT_CMD_HALT;    mutex_lock(&reboot_mutex);    switch (cmd) {case LINUX_REBOOT_CMD_RESTART:    kernel_restart(NULL);    break;case LINUX_REBOOT_CMD_CAD_ON:    C_A_D = 1;    break;case LINUX_REBOOT_CMD_CAD_OFF:    C_A_D = 0;    break;case LINUX_REBOOT_CMD_HALT:    kernel_halt();    do_exit(0);    panic("cannot halt");case LINUX_REBOOT_CMD_POWER_OFF:    kernel_power_off();    do_exit(0);    break;case LINUX_REBOOT_CMD_RESTART2:    if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {ret = -EFAULT;break;    }    buffer[sizeof(buffer) - 1] = '\0';    kernel_restart(buffer);    break;......default:    ret = -EINVAL;    break;    }    mutex_unlock(&reboot_mutex);    return ret;}

在此方法中会根据参数cmd来执行，如果cmd为LINUX_REBOOT_CMD_POWER_OFF，则会执行kernel_power_off方法，然后使用machine_power_off来关闭系统，machine_power_off定义在/kernel/arch/arm/kernel/process.c中。

void kernel_power_off(void){    kernel_shutdown_prepare(SYSTEM_POWER_OFF);    if (pm_power_off_prepare)pm_power_off_prepare();    disable_nonboot_cpus();    syscore_shutdown();    printk(KERN_EMERG "Power down.\n");    kmsg_dump(KMSG_DUMP_POWEROFF);    machine_power_off();}EXPORT_SYMBOL_GPL(kernel_power_off);void machine_power_off(void){    machine_shutdown();    if (pm_power_off)pm_power_off(); // 执行pm_power_off关闭power}

以上就是Android系统的关机流程。

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