概述
我们讲完了SystemServer的启动过程，本节主要来讲解ActivityManagerService的启动过程。ActivityManagerService简称AMS，管理Activity行为，控制Activity的生命周期，派发消息事件，内存管理等功能。
ActivityManagerService启动由SystemServer中startBootstrapService启动
源码分析
private void startBootstrapServices() {
.......
// Activity manager runs the show.
traceBeginAndSlog("StartActivityManager");
// TODO: Might need to move after migration to WM.
//启动ActivityTaskManagerService服务，简称ATM，Android10新引入功能，用来管理Activity的启动，调度等功能。
ActivityTaskManagerService atm = mSystemServiceManager.startService(
ActivityTaskManagerService.Lifecycle.class).getService();
//启动服务ActivityManagerService
mActivityManagerService = ActivityManagerService.Lifecycle.startService(
mSystemServiceManager, atm);
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
mWindowManagerGlobalLock = atm.getGlobalLock();
traceEnd();
}
ATM服务启动过程
ATM启动最终调用的是ActivityTaskManagerService.Lifecycle.onStart()来启动ATM服务的
源码：ActivityTaskManagerService.java#Lifecycle.class
public static final class Lifecycle extends SystemService {
private final ActivityTaskManagerService mService;
public Lifecycle(Context context) {
super(context);
mService = new ActivityTaskManagerService(context);
}
@Override
public void onStart() {
publishBinderService(Context.ACTIVITY_TASK_SERVICE, mService);
mService.start();
}
@Override
public void onUnlockUser(int userId) {
synchronized (mService.getGlobalLock()) {
mService.mStackSupervisor.onUserUnlocked(userId);
}
}
@Override
public void onCleanupUser(int userId) {
synchronized (mService.getGlobalLock()) {
mService.mStackSupervisor.mLaunchParamsPersister.onCleanupUser(userId);
}
}
public ActivityTaskManagerService getService() {
return mService;
}
}
ActivityTaskManagerService对象创建
/**
* System service for managing activities and their containers (task, stacks, displays,... ).
*
* {@hide}
*/
public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
final Context mUiContext;
final ActivityThread mSystemThread;
final ActivityTaskManagerInternal mInternal;
//ActivityStackSupervisor 是ATM中用来管理Activity启动和调度的核心类
public ActivityStackSupervisor mStackSupervisor;
//Activity 容器的根节点
RootActivityContainer mRootActivityContainer;
//WMS 负责窗口的管理
WindowManagerService mWindowManager;
//这是我们目前认为是"Home" Activity的过程
WindowProcessController mHomeProcess;
public ActivityTaskManagerService(Context context) {
//拿到System Context
mContext = context;
mFactoryTest = FactoryTest.getMode();
//取出的是ActivityThread的静态变量sCurrentActivityThread
//这意味着mSystemThread与SystemServer中的ActivityThread一致
mSystemThread = ActivityThread.currentActivityThread();
//拿到System UI Context
mUiContext = mSystemThread.getSystemUiContext();
mLifecycleManager = new ClientLifecycleManager();
//拿到LocalService的对象
mInternal = new LocalService();
GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version", GL_ES_VERSION_UNDEFINED);
}
}
ActivityTaskManagerService.java#start()
将ActivityTaskManagerInternal添加到本地服务的全局注册表中。
ActivityTaskManagerInternal为抽象类，其实现类为ActivityTaskManagerService#LocalService.class
private void start() {
LocalServices.addService(ActivityTaskManagerInternal.class, mInternal);
}
ActivityManagerService服务启动
public static final class Lifecycle extends SystemService {
private final ActivityManagerService mService;
private static ActivityTaskManagerService sAtm;
public Lifecycle(Context context) {
super(context);
//1.创建ActivityManagerService，得到对象，传入ATM的对象
mService = new ActivityManagerService(context, sAtm);
}
@Override
public void onStart() {
mService.start();
}
...
public ActivityManagerService getService() {
return mService;
}
}
AMS对象创建
构造函数初始化主要工作就是初始化一些变量，供之后的service，broadcast，provider的管理和调度
public class ActivityManagerService extends IActivityManager.Stub
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
...
//AMS的运行上下文与SystemServer一致
mContext = systemContext;
...
//取出的是ActivityThread的静态变量sCurrentActivityThread
//这意味着mSystemThread与SystemServer中的ActivityThread一致
mSystemThread = ActivityThread.currentActivityThread();
mUiContext = mSystemThread.getSystemUiContext();
mHandlerThread = new ServiceThread(TAG,
THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
//处理AMS中消息的主力
mHandler = new MainHandler(mHandlerThread.getLooper());
//UiHandler对应于Android中的UiThread
mUiHandler = mInjector.getUiHandler(this);
//创建 BroadcastQueue 前台广播对象，处理超时时长是 10s
mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
"foreground", foreConstants, false);
//创建 BroadcastQueue 后台广播对象，处理超时时长是 60s
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
"background", backConstants, true);
//创建 BroadcastQueue 分流广播对象，处理超时时长是 60s
mOffloadBroadcastQueue = new BroadcastQueue(this, mHandler,
"offload", offloadConstants, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;
mBroadcastQueues[2] = mOffloadBroadcastQueue;
// 创建 ActiveServices 对象，用于管理 ServiceRecord 对象
mServices = new ActiveServices(this);
// 创建 ProviderMap 对象，用于管理 ContentProviderRecord 对象
mProviderMap = new ProviderMap(this);
//得到ATM的对象，调用ATM.initialize
mActivityTaskManager = atm;
mActivityTaskManager.initialize(mIntentFirewall, mPendingIntentController,
DisplayThread.get().getLooper());
//得到ATM的服务信息
mAtmInternal = LocalServices.getService(
ActivityTaskManagerInternal.class);
//加入Watchdog的监控
Watchdog.getInstance().addMonitor(this);
Watchdog.getInstance().addThread(mHandler);
}
}
ActivityManagerService.java#start()
start中做了两件事
- 启动CPU监控线程，在启动CPU监控线程之前，首先将进程复位
- 注册电池状态服务和权限管理服务。
private void start() {
//1.移除所有的进程组
removeAllProcessGroups();
//启动 CPU 监控线程
mProcessCpuThread.start();
//2.注册电池状态和权限管理服务
mBatteryStatsService.publish();
mAppOpsService.publish(mContext);
Slog.d("AppOps", "AppOpsService published");
LocalServices.addService(ActivityManagerInternal.class, new LocalService());
mActivityTaskManager.onActivityManagerInternalAdded();
mUgmInternal.onActivityManagerInternalAdded();
mPendingIntentController.onActivityManagerInternalAdded();
// Wait for the synchronized block started in mProcessCpuThread,
// so that any other access to mProcessCpuTracker from main thread
// will be blocked during mProcessCpuTracker initialization.
try {
mProcessCpuInitLatch.await();
} catch (InterruptedException e) {
Slog.wtf(TAG, "Interrupted wait during start", e);
Thread.currentThread().interrupt();
throw new IllegalStateException("Interrupted wait during start");
}
}
ActivityManagerService最后工作，systemReady()
AMS的systemReady处理分为三个阶段
- 主要是调用一些关键服务的初始化函数， 然后杀死那些没有FLAG_PERSISTENT却在AMS启动完成前已经存在的进程，
同时获取一些配置参数。 需要注意的是，由于只有Java进程才会向AMS注册，而一般的Native进程不会向AMS注册，因此此处杀死的进程是Java进程。
执行goingCallback的处理，主要的工作就是通知一些服务可以进行systemReady、systemRunning相关的工作，并进行启动服务或应用进程的工作
启动Home Activity，当启动结束，并发送ACTION_BOOT_COMPLETED广播时，AMS的启动过程告一段落。
private void startOtherServices() {
...
//安装SettingsProvider.apk
mActivityManagerService.installSystemProviders();
mActivityManagerService.setWindowManager(wm);
//AMS启动完成，完成后续的工作，例如启动桌面等
mActivityManagerService.systemReady(() -> {
阶段1：关键服务的初始化
阶段2：goingCallback处理
阶段3：启动Home Activity，完成AMS启动
...
}, BOOT_TIMINGS_TRACE_LOG);
...
}
阶段1
主要是调用一些关键服务的初始化函数，然后杀死那些没有FLAG_PERSISTENT 却在AMS启动完成前已经存在的进程，同时获取一些配置参数。需要注意的是，由于只有Java进程才会向AMS注册，而一般的Native进程不会向AMS注册，因此此处杀手的进程是Java进程。
//ActivityManagerService.java#systemReady()
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
traceLog.traceBegin("PhaseActivityManagerReady");
synchronized(this) {
//第一次进入mSystemReady为false，不走该流程
if (mSystemReady) {
// If we're done calling all the receivers, run the next "boot phase" passed in
// by the SystemServer
if (goingCallback != null) {
goingCallback.run();
}
return;
}
mLocalDeviceIdleController
= LocalServices.getService(DeviceIdleController.LocalService.class);
mActivityTaskManager.onSystemReady();
//这一部分主要是调用一些关键服务SystemReady相关的函数
//进行一些等待AMS初始完，才能进行的工作
// Make sure we have the current profile info, since it is needed for security checks.
mUserController.onSystemReady();
mAppOpsService.systemReady();
mSystemReady = true;
}
try {
sTheRealBuildSerial = IDeviceIdentifiersPolicyService.Stub.asInterface(
ServiceManager.getService(Context.DEVICE_IDENTIFIERS_SERVICE))
.getSerial();
} catch (RemoteException e) {}
ArrayList procsToKill = null;
synchronized(mPidsSelfLocked) {
for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
ProcessRecord proc = mPidsSelfLocked.valueAt(i);
//在AMS启动完成前，如果没有FLAG_PERSISTENT标志的进程已经启动了 就将这个进程加入到procsToKill中
if (!isAllowedWhileBooting(proc.info)){
if (procsToKill == null) {
procsToKill = new ArrayList();
}
procsToKill.add(proc);
}
}
}
//收集已经启动的进程并杀死，排除persistent常驻进程
synchronized(this) {
//利用removeProcessLocked关闭procsToKill中的进程
if (procsToKill != null) {
for (int i=procsToKill.size()-1; i>=0; i--) {
ProcessRecord proc = procsToKill.get(i);
Slog.i(TAG, "Removing system update proc: " + proc);
mProcessList.removeProcessLocked(proc, true, false, "system update done");
}
}
//至此系统准备完毕
// Now that we have cleaned up any update processes, we
// are ready to start launching real processes and know that
// we won't trample on them any more.
mProcessesReady = true;
}
Slog.i(TAG, "System now ready");
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY, SystemClock.uptimeMillis());
mAtmInternal.updateTopComponentForFactoryTest();
mAtmInternal.getLaunchObserverRegistry().registerLaunchObserver(mActivityLaunchObserver);
watchDeviceProvisioning(mContext);
retrieveSettings();
mUgmInternal.onSystemReady();
final PowerManagerInternal pmi = LocalServices.getService(PowerManagerInternal.class);
if (pmi != null) {
pmi.registerLowPowerModeObserver(ServiceType.FORCE_BACKGROUND_CHECK,
state -> updateForceBackgroundCheck(state.batterySaverEnabled));
updateForceBackgroundCheck(
pmi.getLowPowerState(ServiceType.FORCE_BACKGROUND_CHECK).batterySaverEnabled);
} else {
Slog.wtf(TAG, "PowerManagerInternal not found.");
}
if (goingCallback != null) goingCallback.run();
// Check the current user here as a user can be started inside goingCallback.run() from
// other system services.
final int currentUserId = mUserController.getCurrentUserId();
Slog.i(TAG, "Current user:" + currentUserId);
if (currentUserId != UserHandle.USER_SYSTEM && !mUserController.isSystemUserStarted()) {
// User other than system user has started. Make sure that system user is already
// started before switching user.
throw new RuntimeException("System user not started while current user is:"
+ currentUserId);
}
traceLog.traceBegin("ActivityManagerStartApps");
mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_USER_RUNNING_START,
Integer.toString(currentUserId), currentUserId);
mBatteryStatsService.noteEvent(BatteryStats.HistoryItem.EVENT_USER_FOREGROUND_START,
Integer.toString(currentUserId), currentUserId);
mSystemServiceManager.startUser(currentUserId);
synchronized (this) {
// Only start up encryption-aware persistent apps; once user is
// unlocked we'll come back around and start unaware apps
startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);
// Start up initial activity.
mBooting = true;
// Enable home activity for system user, so that the system can always boot. We don't
// do this when the system user is not setup since the setup wizard should be the one
// to handle home activity in this case.
if (UserManager.isSplitSystemUser() &&
Settings.Secure.getInt(mContext.getContentResolver(),
Settings.Secure.USER_SETUP_COMPLETE, 0) != 0) {
ComponentName cName = new ComponentName(mContext, SystemUserHomeActivity.class);
try {
AppGlobals.getPackageManager().setComponentEnabledSetting(cName,
PackageManager.COMPONENT_ENABLED_STATE_ENABLED, 0,
UserHandle.USER_SYSTEM);
} catch (RemoteException e) {
throw e.rethrowAsRuntimeException();
}
}
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
mAtmInternal.showSystemReadyErrorDialogsIfNeeded();
final int callingUid = Binder.getCallingUid();
final int callingPid = Binder.getCallingPid();
long ident = Binder.clearCallingIdentity();
try {
Intent intent = new Intent(Intent.ACTION_USER_STARTED);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
| Intent.FLAG_RECEIVER_FOREGROUND);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, null, 0, null, null, null, OP_NONE,
null, false, false, MY_PID, SYSTEM_UID, callingUid, callingPid,
currentUserId);
intent = new Intent(Intent.ACTION_USER_STARTING);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, new IIntentReceiver.Stub() {
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser)
throws RemoteException {
}
}, 0, null, null,
new String[] {INTERACT_ACROSS_USERS}, OP_NONE,
null, true, false, MY_PID, SYSTEM_UID, callingUid, callingPid,
UserHandle.USER_ALL);
} catch (Throwable t) {
Slog.wtf(TAG, "Failed sending first user broadcasts", t);
} finally {
Binder.restoreCallingIdentity(ident);
}
mAtmInternal.resumeTopActivities(false /* scheduleIdle */);
mUserController.sendUserSwitchBroadcasts(-1, currentUserId);
BinderInternal.nSetBinderProxyCountWatermarks(BINDER_PROXY_HIGH_WATERMARK,
BINDER_PROXY_LOW_WATERMARK);
BinderInternal.nSetBinderProxyCountEnabled(true);
BinderInternal.setBinderProxyCountCallback(
new BinderInternal.BinderProxyLimitListener() {
@Override
public void onLimitReached(int uid) {
Slog.wtf(TAG, "Uid " + uid + " sent too many Binders to uid "
+ Process.myUid());
BinderProxy.dumpProxyDebugInfo();
if (uid == Process.SYSTEM_UID) {
Slog.i(TAG, "Skipping kill (uid is SYSTEM)");
} else {
killUid(UserHandle.getAppId(uid), UserHandle.getUserId(uid),
"Too many Binders sent to SYSTEM");
}
}
}, mHandler);
traceLog.traceEnd(); // ActivityManagerStartApps
traceLog.traceEnd(); // PhaseActivityManagerReady
}
}
阶段2
执行goingCallback的处理，主要的工作就是通知一些服务可以进行systemReady相关的工作，并进行启动服务或应用进程的工作
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
...
//1.调用参数传入的runnable对象，SystemServer中有具体的定义
if (goingCallback != null) goingCallback.run();
...
//调用所有系统服务的onStartUser接口
mSystemServiceManager.startUser(currentUserId);
synchronized (this) {
//启动persistent为1的application所在的进程
startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);
// Start up initial activity.
mBooting = true;
...
}
goingCallBack.run()
监控Native的crash，启动WebView，执行一些服务的systemReady和systemRunning方法
private void startOtherServices() {
mActivityManagerService.systemReady(() -> {
//阶段 550
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);
...
//监控Native的crash
mActivityManagerService.startObservingNativeCrashes();
, BOOT_TIMINGS_TRACE_LOG);
...
//启动WebView
mWebViewUpdateService.prepareWebViewInSystemServer();
//启动systemUI
startSystemUi(context, windowManagerF);
// 执行一系列服务的systemReady方法
networkManagementF.systemReady();
ipSecServiceF.systemReady();
networkStatsF.systemReady();
connectivityF.systemReady();
networkPolicyF.systemReady(networkPolicyInitReadySignal);
...
//阶段 600
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
//执行一系列服务的systemRunning方法
locationF.systemRunning();
countryDetectorF.systemRunning();
networkTimeUpdaterF.systemRunning();
inputManagerF.systemRunning();
telephonyRegistryF.systemRunning();
mediaRouterF.systemRunning();
mmsServiceF.systemRunning();
...
}
阶段3
启动Home Activity，当启动结束，发送ACTION_BOOT_COMPLETED广播时，AMS的启动过程告一段落
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
...
//1.通过ATM，启动Home Activity
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
...
//2.发送一些广播消息
try {
//system发送广播 ACTION_USER_STARTED = "android.intent.action.USER_STARTED";
Intent intent = new Intent(Intent.ACTION_USER_STARTED);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
| Intent.FLAG_RECEIVER_FOREGROUND);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, null, 0, null, null, null, OP_NONE,
null, false, false, MY_PID, SYSTEM_UID, callingUid, callingPid,
currentUserId);
//system发送广播 ACTION_USER_STARTING= "android.intent.action.USER_STARTING";
intent = new Intent(Intent.ACTION_USER_STARTING);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
intent.putExtra(Intent.EXTRA_USER_HANDLE, currentUserId);
broadcastIntentLocked(null, null, intent,
null, new IIntentReceiver.Stub() {
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser)
throws RemoteException {
}
}, 0, null, null,
new String[] {INTERACT_ACROSS_USERS}, OP_NONE,
null, true, false, MY_PID, SYSTEM_UID, callingUid, callingPid,
UserHandle.USER_ALL);
} catch (Throwable t) {
Slog.wtf(TAG, "Failed sending first user broadcasts", t);
} finally {
Binder.restoreCallingIdentity(ident);
}
}
ActivityTaskManagerService.java#startHomeOnAllDisplays
启动Home Activity
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
//调用RootActivityContainer的startHomeOnAllDisplays()，最终到startHomeOnDisplay()
return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);
}
}
#RootActivityContainer.java
boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
boolean fromHomeKey) {
// Fallback to top focused display if the displayId is invalid.
if (displayId == INVALID_DISPLAY) {
displayId = getTopDisplayFocusedStack().mDisplayId;
}
Intent homeIntent = null;
ActivityInfo aInfo = null;
if (displayId == DEFAULT_DISPLAY) {
//home intent有CATEGORY_HOME
homeIntent = mService.getHomeIntent();
//根据intent中携带的ComponentName，利用PKMS得到ActivityInfo
aInfo = resolveHomeActivity(userId, homeIntent);
} else if (shouldPlaceSecondaryHomeOnDisplay(displayId)) {
Pair info =
RootActivityContainerMifavor.resolveSecondaryHomeActivityPcMode(this, userId, displayId);
aInfo = info.first;
homeIntent = info.second;
}
if (aInfo == null || homeIntent == null) {
return false;
}
if (!canStartHomeOnDisplay(aInfo, displayId, allowInstrumenting)) {
return false;
}
// Updates the home component of the intent.
homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
// Updates the extra information of the intent.
if (fromHomeKey) {
homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);
}
// Update the reason for ANR debugging to verify if the user activity is the one that
// actually launched.
final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(
aInfo.applicationInfo.uid) + ":" + displayId;
//启动Home Activity--Luncher
mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
displayId);
return true;
}
总结
AMS的启动主要经历了如下几个阶段：
- 为SystemServer进程创建Android运行环境，例如System Context
启动AMS，做一些初始化的工作 - 将SystemServer进程纳入到AMS的进程管理体系中
- AMS启动完成，通知服务或应用完成后续的工作，调用一些服务的systemReady()方法中，
- 启动Lanucher，完成AMS的启动工作