Android系统关机重启流程（一）
借鉴参考：
http://gityuan.com/2016/07/09/android-reboot/#28-sdtrebootorshutdown
https://blog.csdn.net/anlory/article/details/85010689
一，概述
重启动作从按键触发中断，linux kernel层给Android framework层返回按键事件进入 framework层，再从 framework层到kernel层执行kernel层关机任务，当然还有非按键触发，比如shell 命令reboot，或者系统异常导致重启，或者直接调用PM的reboot()方法重启。
这里就先从PowerManager说起。
二，重启流程
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java
frameworks/base/services/core/java/com/android/server/power/ShutdownThread.java
frameworks/base/core/java/android/os/PowerManager.java
2.1 PM.reboot
[->PowerManager.java]
public void reboot(String reason) {
try {
mService.reboot(false, reason, true); // 调用PowerManagerService->reboot
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
2.2 BinderService.reboot
[-> PowerManagerService.java]
private final class BinderService extends IPowerManager.Stub {
/**
* Reboots the device.
*
* @param confirm If true, shows a reboot confirmation dialog.
* @param reason The reason for the reboot, or null if none.
* @param wait If true, this call waits for the reboot to complete and does not return.
*/
@Override // Binder call
public void reboot(boolean confirm, String reason, boolean wait) {
//检查权限，reboot权限和reason是recovery时检查recovery权限
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);
if (PowerManager.REBOOT_RECOVERY.equals(reason)
|| PowerManager.REBOOT_RECOVERY_UPDATE.equals(reason)) {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.RECOVERY, null);
}
final long ident = Binder.clearCallingIdentity();
try {
shutdownOrRebootInternal(HALT_MODE_REBOOT, confirm, reason, wait);
} finally {
Binder.restoreCallingIdentity(ident);
}
}
}
此时参数为shutdownOrRebootInternal(false, false, reason, true);
shutdown=false：代表重启；
confirm=false：代表直接重启，无需弹出询问提示框；
reason 可能为recovery、bootloader、shutdown等
wait=true：代表阻塞等待重启操作完成。
2.3 PMS.shutdownOrRebootInternal
[-> PowerManagerService.java]
private void shutdownOrRebootInternal(final @HaltMode int haltMode, final boolean confirm,
final String reason, boolean wait) {
...
Runnable runnable = new Runnable() {
@Override
public void run() {
synchronized (this) {
//根据haltMode 区分，reboot，shutdown，rebootsafemode
if (haltMode == HALT_MODE_REBOOT_SAFE_MODE) {
ShutdownThread.rebootSafeMode(getUiContext(), confirm);
} else if (haltMode == HALT_MODE_REBOOT) {
ShutdownThread.reboot(getUiContext(), reason, confirm);
} else {
ShutdownThread.shutdown(getUiContext(), reason, confirm);
}
}
}
};
// ShutdownThread must run on a looper capable of displaying the UI.
//// ShutdownThread必须运行在一个展现UI的looper
Message msg = Message.obtain(UiThread.getHandler(), runnable);
msg.setAsynchronous(true);
UiThread.getHandler().sendMessage(msg);
// PowerManager.reboot() is documented not to return so just wait for the inevitable.
if (wait) {
//等待ShutdownThread执行完毕
synchronized (runnable) {
while (true) {
try {
runnable.wait();
} catch (InterruptedException e) {
}
}
}
}
}
2.4 SDT.reboot
[->ShutdownThread.java]
public static void reboot(final Context context, String reason, boolean confirm) {
mReboot = true;
mRebootSafeMode = false;
mRebootHasProgressBar = false;
mReason = reason;
shutdownInner(context, confirm);
}
mReboot为true则代表重启操作，值为false则代表关机操作。
2.5 SDT.shutdownInner
[->ShutdownThread.java]
private static void shutdownInner(final Context context, boolean confirm) {
// ShutdownThread is called from many places, so best to verify here that the context passed
// in is themed.
context.assertRuntimeOverlayThemable();
// ensure that only one thread is trying to power down.
// any additional calls are just returned
////确保只有唯一的线程执行shutdown/reboot操作
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);
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);
/* longPressBehavior 并没有什么意义，只配置长按power键时弹窗power off选项还是语音助手。
-- Control the behavior when the user long presses the power button.
0 - Nothing
1 - Global actions menu
2 - Power off (with confirmation)
3 - Power off (without confirmation)
4 - Go to voice assist
*/
Log.d(TAG, "Notifying thread to start shutdown longPressBehavior=" + longPressBehavior);
if (confirm) {
//这里是走弹出关机/重启提示框
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 {
//本次confirm=false ，直接走这里
beginShutdownSequence(context);
}
}
2.6 SDT.beginShutdownSequence
[->ShutdownThread.java]
private static void beginShutdownSequence(Context context) {
synchronized (sIsStartedGuard) {
if (sIsStarted) {
Log.d(TAG, "Shutdown sequence already running, returning.");
return; //shutdown操作正在执行，则直接返回
}
sIsStarted = true;
}
sInstance.mProgressDialog = showShutdownDialog(context);
sInstance.mContext = context;
sInstance.mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
// make sure we never fall asleep again
//确保系统不会进入休眠状态
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
//当处理亮屏状态，则获取亮屏锁，提供用户体验
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;
}
}
if (SecurityLog.isLoggingEnabled()) {
SecurityLog.writeEvent(SecurityLog.TAG_OS_SHUTDOWN);
}
// start the thread that initiates shutdown
sInstance.mHandler = new Handler() {
};
//启动线程来执行shutdown初始化
sInstance.start(); //接下来会启动shutdownThread.run
}
2.7 SDT.run
[->ShutdownThread.java]
/**
* Makes sure we handle the shutdown gracefully.
* Shuts off power regardless of radio state if the allotted time has passed.
*/
public void run() {
TimingsTraceLog shutdownTimingLog = newTimingsLog();
shutdownTimingLog.traceBegin("SystemServerShutdown");
metricShutdownStart();//用来统计关机时间
metricStarted(METRIC_SYSTEM_SERVER);
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();
}
};
/*
* 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") + (mReason != null ? mReason : "");
SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
//设置属性"sys.shutdown.requested"的值为reason
}
/*
* If we are rebooting into safe mode, write a system property
* indicating so.
*/
if (mRebootSafeMode) {
//如果需要重启进入安全模式，则设置"persist.sys.safemode"=1
SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
}
metricStarted(METRIC_SEND_BROADCAST);
shutdownTimingLog.traceBegin("SendShutdownBroadcast");
Log.i(TAG, "Sending shutdown broadcast...");
// First send the high-level shut down broadcast.
//1. 发送关机广播
mActionDone = false;
Intent intent = new Intent(Intent.ACTION_SHUTDOWN);
intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND | Intent.FLAG_RECEIVER_REGISTERED_ONLY);
mContext.sendOrderedBroadcastAsUser(intent,
UserHandle.ALL, null, br, mHandler, 0, null, null);
final long endTime = SystemClock.elapsedRealtime() + MAX_BROADCAST_TIME;
synchronized (mActionDoneSync) {
//循环等待,超时或者mActionDone都会结束该循环
while (!mActionDone) {
long delay = endTime - SystemClock.elapsedRealtime();
if (delay <= 0) {
Log.w(TAG, "Shutdown broadcast timed out");
break;
} else if (mRebootHasProgressBar) {
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, ACTION_DONE_POLL_WAIT_MS));
} catch (InterruptedException e) {
}
}
}
if (mRebootHasProgressBar) {//设置reboot进程条
sInstance.setRebootProgress(BROADCAST_STOP_PERCENT, null);
}
shutdownTimingLog.traceEnd(); // SendShutdownBroadcast
metricEnded(METRIC_SEND_BROADCAST);
Log.i(TAG, "Shutting down activity manager...");
shutdownTimingLog.traceBegin("ShutdownActivityManager");
metricStarted(METRIC_AM);
//2. 关闭AMS
final IActivityManager am =
IActivityManager.Stub.asInterface(ServiceManager.checkService("activity"));
if (am != null) {
try {
am.shutdown(MAX_BROADCAST_TIME);
} catch (RemoteException e) {
}
}
if (mRebootHasProgressBar) {
sInstance.setRebootProgress(ACTIVITY_MANAGER_STOP_PERCENT, null);
}
shutdownTimingLog.traceEnd();// ShutdownActivityManager
metricEnded(METRIC_AM);
Log.i(TAG, "Shutting down package manager...");
shutdownTimingLog.traceBegin("ShutdownPackageManager");
metricStarted(METRIC_PM);
//3. 关闭PMS
final PackageManagerService pm = (PackageManagerService)
ServiceManager.getService("package");
if (pm != null) {
pm.shutdown();
}
if (mRebootHasProgressBar) {
sInstance.setRebootProgress(PACKAGE_MANAGER_STOP_PERCENT, null);
}
shutdownTimingLog.traceEnd(); // ShutdownPackageManager
metricEnded(METRIC_PM);
// Shutdown radios.
//4. 关闭radios
shutdownTimingLog.traceBegin("ShutdownRadios");
metricStarted(METRIC_RADIOS);
shutdownRadios(MAX_RADIO_WAIT_TIME);
if (mRebootHasProgressBar) {
sInstance.setRebootProgress(RADIO_STOP_PERCENT, null);
}
shutdownTimingLog.traceEnd(); // ShutdownRadios
metricEnded(METRIC_RADIOS);
if (mRebootHasProgressBar) {
sInstance.setRebootProgress(MOUNT_SERVICE_STOP_PERCENT, null);
// If it's to reboot to install an update and uncrypt hasn't been
// done yet, trigger it now.
uncrypt();
}
shutdownTimingLog.traceEnd(); // SystemServerShutdown
metricEnded(METRIC_SYSTEM_SERVER);
saveMetrics(mReboot, mReason);
// Remaining work will be done by init, including vold shutdown
//关机剩下得动作由init完成，包括void，下一节分析
rebootOrShutdown(mContext, mReboot, mReason);
}
设置”sys.shutdown.requested”，记录下mReboot和mReason。如果是进入安全模式，则”persist.sys.safemode=1”。
接下来主要关闭一些系统服务：
发送关机广播
关闭AMS
关闭PMS
关闭radios
之后就需要进入重启/关机流程，由init 进程处理。
2.7.1 AMS.shutdown
通过AMP.shutdown，通过binder调用到AMS.shutdown.
[->ActivityManagerService.java]
@Override
public boolean shutdown(int timeout) {
////权限检测
if (checkCallingPermission(android.Manifest.permission.SHUTDOWN)
!= PackageManager.PERMISSION_GRANTED) {
throw new SecurityException("Requires permission "
+ android.Manifest.permission.SHUTDOWN);
}
boolean timedout = false;
synchronized(this) {
mShuttingDown = true;
mStackSupervisor.prepareForShutdownLocked();
//禁止WMS继续处理Event
updateEventDispatchingLocked();
//调用ASS处理shutdown操作
timedout = mStackSupervisor.shutdownLocked(timeout);
}
mAppOpsService.shutdown();
if (mUsageStatsService != null) {
mUsageStatsService.prepareShutdown();
}
mBatteryStatsService.shutdown();
synchronized (this) {
mProcessStats.shutdownLocked();
notifyTaskPersisterLocked(null, true);
}
return timedout;
}
此处timeout为MAX_BROADCAST_TIME=10s
2.7.2 PMS.shutdown
public void shutdown() {
mPackageUsage.write(true);
}
此处mPackageUsage数据类型是PMS的内部类PackageUsage。
private class PackageUsage {
void write(boolean force) {
if (force) {
writeInternal();
return;
}
...
}
}
对于force=true，接下来调用writeInternal方法。
private class PackageUsage {
private void writeInternal() {
synchronized (mPackages) {
synchronized (mFileLock) {
//file是指/data/system/package-usage.list
AtomicFile file = getFile();
FileOutputStream f = null;
try {
//将原来的文件记录到package-usage.list.bak
f = file.startWrite();
BufferedOutputStream out = new BufferedOutputStream(f);
FileUtils.setPermissions(file.getBaseFile().getPath(), 0640, SYSTEM_UID, PACKAGE_INFO_GID);
StringBuilder sb = new StringBuilder();
for (PackageParser.Package pkg : mPackages.values()) {
if (pkg.mLastPackageUsageTimeInMills == 0) {
continue;
}
sb.setLength(0);
sb.append(pkg.packageName);
sb.append(' ');
sb.append((long)pkg.mLastPackageUsageTimeInMills);
sb.append('\n');
out.write(sb.toString().getBytes(StandardCharsets.US_ASCII));
}
out.flush();
//将文件内容同步到磁盘，并删除.bak文件
file.finishWrite(f);
} catch (IOException e) {
if (f != null) {
file.failWrite(f);
}
Log.e(TAG, "Failed to write package usage times", e);
}
}
}
mLastWritten.set(SystemClock.elapsedRealtime());
}
}
/data/system/package-usage.list文件中每一行记录一条package及其上次使用时间(单位ms)。
由于IO操作的过程中，写入文件并非立刻就会真正意义上写入物理磁盘，以及在写入文件的过程中还可能中断或者出错等原因的考虑，采用的策略是先将老的文件package-usage.list，重命为增加后缀package-usage.list.bak；然后再往package-usage.list文件写入新的数据，数据写完之后再执行sync操作，将内存数据彻底写入物理磁盘，此时便可以安全地删除原来的package-usage.list.bak文件。
2.7.3 ST.shutdownRadios
[-> ShutdownThread.java]
private void shutdownRadios(final int timeout) {
// If a radio is wedged, disabling it may hang so we do this work in another thread,
// just in case.
final long endTime = SystemClock.elapsedRealtime() + timeout;
final boolean[] done = new boolean[1];
Thread t = new Thread() {
public void run() {
TimingsTraceLog shutdownTimingsTraceLog = newTimingsLog();
boolean radioOff;
final ITelephony phone =
ITelephony.Stub.asInterface(ServiceManager.checkService("phone"));
try {
radioOff = phone == null || !phone.needMobileRadioShutdown();
if (!radioOff) {
Log.w(TAG, "Turning off cellular radios...");
metricStarted(METRIC_RADIO);
phone.shutdownMobileRadios();
}
} catch (RemoteException ex) {
Log.e(TAG, "RemoteException during radio shutdown", ex);
radioOff = true;
}
Log.i(TAG, "Waiting for Radio...");
long delay = endTime - SystemClock.elapsedRealtime();
while (delay > 0) {
if (mRebootHasProgressBar) {
int status = (int)((timeout - delay) * 1.0 *
(RADIO_STOP_PERCENT - PACKAGE_MANAGER_STOP_PERCENT) / timeout);
status += PACKAGE_MANAGER_STOP_PERCENT;
sInstance.setRebootProgress(status, null);
}
if (!radioOff) {
try {
radioOff = !phone.needMobileRadioShutdown();
} catch (RemoteException ex) {
Log.e(TAG, "RemoteException during radio shutdown", ex);
radioOff = true;
}
if (radioOff) {
Log.i(TAG, "Radio turned off.");
metricEnded(METRIC_RADIO);
shutdownTimingsTraceLog
.logDuration("ShutdownRadio", TRON_METRICS.get(METRIC_RADIO));
}
}
if (radioOff) {
Log.i(TAG, "Radio shutdown complete.");
done[0] = true;
break;
}
SystemClock.sleep(RADIOS_STATE_POLL_SLEEP_MS);
delay = endTime - SystemClock.elapsedRealtime();
}
}
};
t.start();
try {
t.join(timeout);
} catch (InterruptedException ex) {
}
if (!done[0]) {
Log.w(TAG, "Timed out waiting for Radio shutdown.");
}
}
创建新的线程来处理NFC, Radio and Bluetooth这些射频相关的模块的shutdown过程。每间隔500ms，check一次，直到nfc、bluetooth、radio全部关闭或者超时(MAX_RADIO_WAIT_TIME=12s)才会退出循环。
2.8 SDT.rebootOrShutdown
[-> ShutdownThread.java]
/**
* Do not call this directly. Use {@link #reboot(Context, String, boolean)}
* or {@link #shutdown(Context, String, 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/shutdown
*/
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");
reason = null;
} 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
//关闭电源 [见流程2.10]
Log.i(TAG, "Performing low-level shutdown...");
PowerManagerService.lowLevelShutdown(reason);
}
对于重启原因:
logcat会直接输出Rebooting, reason: ;
如果重启失败，则会输出Reboot failed; ，- 果无法重启，则会尝试直接关机。
2.9 PMS.lowLevelReboot
public static void lowLevelShutdown(String reason) {
if (reason == null) {
reason = "";
}
SystemProperties.set("sys.powerctl", "shutdown," + reason);
}
/**
* 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 the reason is "quiescent", it means that the boot process should proceed
// without turning on the screen/lights.
// The "quiescent" property is sticky, meaning that any number
// of subsequent reboots should honor the property until it is reset.
if (reason.equals(PowerManager.REBOOT_QUIESCENT)) {
sQuiescent = true;
reason = "";
} else if (reason.endsWith("," + PowerManager.REBOOT_QUIESCENT)) {
sQuiescent = true;
reason = reason.substring(0,
reason.length() - PowerManager.REBOOT_QUIESCENT.length() - 1);
}
if (reason.equals(PowerManager.REBOOT_RECOVERY)
|| reason.equals(PowerManager.REBOOT_RECOVERY_UPDATE)) {
reason = "recovery";
}
if (sQuiescent) {
// Pass the optional "quiescent" argument to the bootloader to let it know
// that it should not turn the screen/lights on.
reason = reason + ",quiescent";
}
SystemProperties.set("sys.powerctl", "reboot," + reason);
try {
Thread.sleep(20 * 1000L);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
Slog.wtf(TAG, "Unexpected return from lowLevelReboot!");
}
当reboot原因是“recovery”，则设置属性sys.powerctl=reboot,recovery；
当其他情况，则设置属性”sys.powerctl=reboot,[reason]”。
当关机时，则设置属性”sys.powerctl=shutdown,[reason]”。
到此，framework层面的重启就流程基本介绍完了，那么接下来就要进入属性服务，即getprop sys.powerctl reboot,
三，总结
先用一句话总结，从最开始的PM.reboot()，经过层层调用，最终重启的核心方法等价于调用SystemProperties.set(“sys.powerctl”, “reboot,” + reason); 也就意味着调用下面命令，也能重启手机：
adb shell setprop sys.powerctl reboot
后续,还会进一步上面命令的执行流程，如何进入native，如何进入kernel来完成重启的，以及PM.reboot如何触发的。