android中的重启或者关机操作有很多种情况，包括Power键长按关机/重启、恢复出厂设置重启、低电量关机等等，这些事件经过一系列的判断处理最终都会通过调用PowerManagerService.java类然后调入到ShutdownThread.java类里面，最终都是从这个类的shutdownInner()方法开始的;
shutdownInner()这个方法很长，主要的作用是创建弹出框，根据传入参数confirm来判断是否显示需要用户确认关机或者重启的Dialog，然后调用beginShutdownSequence()方法去开线程执行关机或者重启操作。
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;
}
}
boolean showRebootOption = false;
String[] defaultActions = context.getResources().getStringArray(
com.android.internal.R.array.config_globalActionsList);
for (int i = 0; i < defaultActions.length; i++) {
if (defaultActions[i].equals("reboot")) {
showRebootOption = true;
break;
}
}
final int longPressBehavior = context.getResources().getInteger(
com.android.internal.R.integer.config_longPressOnPowerBehavior);
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);
if (showRebootOption && !mRebootSafeMode) {
resourceId = com.android.internal.R.string.reboot_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
: showRebootOption
? com.android.internal.R.string.reboot_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);
}
} private static void beginShutdownSequence(Context context) {
synchronized (sIsStartedGuard) {
if (sIsStarted) {
Log.d(TAG, "Shutdown sequence already running, returning.");
return;
}
sIsStarted = true;
}
// Throw up a system dialog to indicate the device is rebooting / shutting down.
ProgressDialog pd = new ProgressDialog(context);
// Path 1: Reboot to recovery and install the update
// Condition: mRebootReason == REBOOT_RECOVERY and mRebootUpdate == True
// (mRebootUpdate is set by checking if /cache/recovery/uncrypt_file exists.)
// UI: progress bar
//
// Path 2: Reboot to recovery for factory reset
// Condition: mRebootReason == REBOOT_RECOVERY
// UI: spinning circle only (no progress bar)
//
// Path 3: Regular reboot / shutdown
// Condition: Otherwise
// UI: spinning circle only (no progress bar)
if (PowerManager.REBOOT_RECOVERY.equals(mRebootReason)) {
mRebootUpdate = new File(UNCRYPT_PACKAGE_FILE).exists();
if (mRebootUpdate) {
pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_update_title));
pd.setMessage(context.getText(
com.android.internal.R.string.reboot_to_update_prepare));
pd.setMax(100);
pd.setProgressNumberFormat(null);
pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pd.setProgress(0);
pd.setIndeterminate(false);
} else {
// Factory reset path. Set the dialog message accordingly.
pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_reset_title));
pd.setMessage(context.getText(
com.android.internal.R.string.reboot_to_reset_message));
pd.setIndeterminate(true);
}
} else {
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.mProgressDialog = pd;
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() {
};
sInstance.start();
}1、显示一个系统进度dialog表示当前设备正在关机/重启;
2、持CPU锁、屏幕锁，保持设备处于唤醒态、屏幕处于亮屏态;
3、最后启动线程，执行run方法，这个线程指的是ShutThread.java，执行的run()方法，也是这个类的run()方法。
run()方法的篇幅更长，不适合贴代码，接下来分块来分析：
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();
}
}; void actionDone() {
synchronized (mActionDoneSync) {
mActionDone = true;
mActionDoneSync.notifyAll();
}
} // 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);
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;
} else if (mRebootUpdate) {
int status = (int)((MAX_BROADCAST_TIME - delay) * 1.0 *
BROADCAST_STOP_PERCENT / MAX_BROADCAST_TIME);
sInstance.setRebootProgress(status, null);
}
try {
mActionDoneSync.wait(Math.min(delay, PHONE_STATE_POLL_SLEEP_MSEC));
} catch (InterruptedException e) {
}
}
}2、等待Intent.ACTION_SHUTDOWN有序广播全部处理完成,也就是等上面的br.onReveive回调;
3、然后调用actionDone()方法，使得代码可以继续往下执行;
ActivityManagerService执行shutdown()操作，保存一些相关状态(比如battery).
final IActivityManager am =
ActivityManagerNative.asInterface(ServiceManager.checkService("activity"));
if (am != null) {
try {
am.shutdown(MAX_BROADCAST_TIME);
} catch (RemoteException e) {
}
} final PackageManagerService pm = (PackageManagerService)
ServiceManager.getService("package");
if (pm != null) {
pm.shutdown();
} // Shutdown 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);
} 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;
} else if (mRebootUpdate) {
int status = (int)((MAX_SHUTDOWN_WAIT_TIME - delay) * 1.0 *
(MOUNT_SERVICE_STOP_PERCENT - RADIO_STOP_PERCENT) /
MAX_SHUTDOWN_WAIT_TIME);
status += RADIO_STOP_PERCENT;
sInstance.setRebootProgress(status, null);
}
try {
mActionDoneSync.wait(Math.min(delay, PHONE_STATE_POLL_SLEEP_MSEC));
} catch (InterruptedException e) {
}
}
}rebootOrShutdown(mContext, mReboot, mRebootReason); /**
* Do not call this directly. Use {@link #reboot(Context, String, boolean)}
* or {@link #shutdown(Context, boolean)} instead.
*
* @param context Context used to vibrate or null without vibration
* @param reboot true to reboot or false to shutdown
* @param reason reason for reboot
*/
public static void rebootOrShutdown(final Context context, 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 && context != null) {
// vibrate before shutting down
Vibrator vibrator = new SystemVibrator(context);
try {
vibrator.vibrate(SHUTDOWN_VIBRATE_MS, VIBRATION_ATTRIBUTES);
} 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();
}PowerManagerService.lowLevelReboot(reason);PowerManagerService.lowLevelShutdown();先来看lowLevelShutdown()方法： /**
* 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");
}再来看lowLevelReboot()方法：
/**
* Low-level function to reboot the device. On success, this
* function doesn't return. If more than 20 seconds passes from
* the time a reboot is requested, this method returns.
*
* @param reason code to pass to the kernel (e.g. "recovery"), or null.
*/
public static void lowLevelReboot(String reason) {
if (reason == null) {
reason = "";
}
if (reason.equals(PowerManager.REBOOT_RECOVERY)) {
// If we are rebooting to go into recovery, instead of
// setting sys.powerctl directly we'll start the
// pre-recovery service which will do some preparation for
// recovery and then reboot for us.
SystemProperties.set("ctl.start", "pre-recovery");
} else {
SystemProperties.set("sys.powerctl", "reboot," + reason);
}
try {
Thread.sleep(20 * 1000L);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
Slog.wtf(TAG, "Unexpected return from lowLevelReboot!");
}至此，Java层reboot & shutdown流程分析结束。
reboot & shutdown流程总结：
1、不管是reboot还是shutdown最终都会调入到ShutdownThread.java类里的shutdownInner()方法;
2、ShutdownThread.java继承于Thread.java，这个类的核心方法还是run()方法;
3、在run()方法内，发起有序shutdown广播;执行ActivityManagerService，PackageManagerService，nfc、电话服务相关、蓝牙等无线模块，文件系统挂载服务等的shutdown工作;
4、shutdown操作会导致设备震动500ms;
5、java层的最终实现是在PowerManagerService.java，从这里进入native层;通过系统属性类SystemProperties.java触发shutdown & reboot的相关操作。