菜鸟学Android源码－System Server服务启动(Launcher调起)

本文主要是介绍菜鸟学Android源码－System Server服务启动(Launcher调起)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

(PS:本博客内所有源码均是Android N版本)
接上篇文章，我们转入SystemServer.java这个类中学习，该类位于/framework/base/services/java/com/android/server/

查看该类的main函数，具体代码如下：

public static void main(String[] args) {new SystemServer().run();}

从上面可以看出SystemServer.java必然实现了Runnable接口，其核心逻辑应该位于run方法中，查看run方法细节代码如下：

private void run() {try {Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "InitBeforeStartServices");// If a device's clock is before 1970 (before 0), a lot of// APIs crash dealing with negative numbers, notably// java.io.File#setLastModified, so instead we fake it and// hope that time from cell towers or NTP fixes it shortly.if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {Slog.w(TAG, "System clock is before 1970; setting to 1970.");SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);}// If the system has "persist.sys.language" and friends set, replace them with// "persist.sys.locale". Note that the default locale at this point is calculated// using the "-Duser.locale" command line flag. That flag is usually populated by// AndroidRuntime using the same set of system properties, but only the system_server// and system apps are allowed to set them.//// NOTE: Most changes made here will need an equivalent change to// core/jni/AndroidRuntime.cppif (!SystemProperties.get("persist.sys.language").isEmpty()) {final String languageTag = Locale.getDefault().toLanguageTag();SystemProperties.set("persist.sys.locale", languageTag);SystemProperties.set("persist.sys.language", "");SystemProperties.set("persist.sys.country", "");SystemProperties.set("persist.sys.localevar", "");}// Here we go!Slog.i(TAG, "Entered the Android system server!");EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, SystemClock.uptimeMillis());// In case the runtime switched since last boot (such as when// the old runtime was removed in an OTA), set the system// property so that it is in sync. We can't do this in// libnativehelper's JniInvocation::Init code where we already// had to fallback to a different runtime because it is// running as root and we need to be the system user to set// the property. http://b/11463182SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());// Enable the sampling profiler.if (SamplingProfilerIntegration.isEnabled()) {SamplingProfilerIntegration.start();mProfilerSnapshotTimer = new Timer();mProfilerSnapshotTimer.schedule(new TimerTask() {@Overridepublic void run() {SamplingProfilerIntegration.writeSnapshot("system_server", null);}}, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);}// Mmmmmm... more memory!VMRuntime.getRuntime().clearGrowthLimit();// The system server has to run all of the time, so it needs to be// as efficient as possible with its memory usage.VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);// Some devices rely on runtime fingerprint generation, so make sure// we've defined it before booting further.Build.ensureFingerprintProperty();// Within the system server, it is an error to access Environment paths without// explicitly specifying a user.Environment.setUserRequired(true);// Within the system server, any incoming Bundles should be defused// to avoid throwing BadParcelableException.BaseBundle.setShouldDefuse(true);// Ensure binder calls into the system always run at foreground priority.BinderInternal.disableBackgroundScheduling(true);// Increase the number of binder threads in system_serverBinderInternal.setMaxThreads(sMaxBinderThreads);// Prepare the main looper thread (this thread).android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);android.os.Process.setCanSelfBackground(false);Looper.prepareMainLooper();// Initialize native services.System.loadLibrary("android_servers");// Check whether we failed to shut down last time we tried.// This call may not return.performPendingShutdown();// Initialize the system context.createSystemContext();// Create the system service manager.mSystemServiceManager = new SystemServiceManager(mSystemContext);LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);} finally {Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}// Start services.try {Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartServices");startBootstrapServices();startCoreServices();startOtherServices();} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}// For debug builds, log event loop stalls to dropbox for analysis.if (StrictMode.conditionallyEnableDebugLogging()) {Slog.i(TAG, "Enabled StrictMode for system server main thread.");}// Loop forever.Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");}

从上面我们可以看到在设置一些系统启动的环境变量，例如说系统时间，语言，是否支持指纹等，其后进行了如下代码操作：

            startBootstrapServices();startCoreServices();startOtherServices();

从上面函数名我们就可以看出，这里开始启动系统相关的所有服务，startBootstrapServices();启动的是一些底层服务，例如PowerManagerService，LightsService，DisplayManagerService等系统正常运作的底层基础服务。startCoreServices();启动的是没有挂载在启动进程的服务。startOtherServices();是我们关注的重心，在这里我们要找到系统调起Launcher的过程。
在startOtherService()这个函数中，我们重点关注系统准备完成后的动作，找到如下代码：

// We now tell the activity manager it is okay to run third party// code.  It will call back into us once it has gotten to the state// where third party code can really run (but before it has actually// started launching the initial applications), for us to complete our// initialization.mActivityManagerService.systemReady(new Runnable() {@Overridepublic void run() {Slog.i(TAG, "Making services ready");mSystemServiceManager.startBootPhase(SystemService.PHASE_ACTIVITY_MANAGER_READY);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "PhaseActivityManagerReady");Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartObservingNativeCrashes");try {mActivityManagerService.startObservingNativeCrashes();} catch (Throwable e) {reportWtf("observing native crashes", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);if (!mOnlyCore) {Slog.i(TAG, "WebViewFactory preparation");Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "WebViewFactoryPreparation");mWebViewUpdateService.prepareWebViewInSystemServer();Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartSystemUI");try {startSystemUi(context);} catch (Throwable e) {reportWtf("starting System UI", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkScoreReady");try {if (networkScoreF != null) networkScoreF.systemReady();} catch (Throwable e) {reportWtf("making Network Score Service ready", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkManagementServiceReady");try {if (networkManagementF != null) networkManagementF.systemReady();} catch (Throwable e) {reportWtf("making Network Managment Service ready", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkStatsServiceReady");try {if (networkStatsF != null) networkStatsF.systemReady();} catch (Throwable e) {reportWtf("making Network Stats Service ready", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeNetworkPolicyServiceReady");try {if (networkPolicyF != null) networkPolicyF.systemReady();} catch (Throwable e) {reportWtf("making Network Policy Service ready", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeConnectivityServiceReady");try {if (connectivityF != null) connectivityF.systemReady();} catch (Throwable e) {reportWtf("making Connectivity Service ready", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Watchdog.getInstance().start();// It is now okay to let the various system services start their// third party code...Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "PhaseThirdPartyAppsCanStart");mSystemServiceManager.startBootPhase(SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);try {if (locationF != null) locationF.systemRunning();} catch (Throwable e) {reportWtf("Notifying Location Service running", e);}try {if (countryDetectorF != null) countryDetectorF.systemRunning();} catch (Throwable e) {reportWtf("Notifying CountryDetectorService running", e);}try {if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemRunning();} catch (Throwable e) {reportWtf("Notifying NetworkTimeService running", e);}try {if (commonTimeMgmtServiceF != null) {commonTimeMgmtServiceF.systemRunning();}} catch (Throwable e) {reportWtf("Notifying CommonTimeManagementService running", e);}try {if (atlasF != null) atlasF.systemRunning();} catch (Throwable e) {reportWtf("Notifying AssetAtlasService running", e);}try {// TODO(BT) Pass parameter to input managerif (inputManagerF != null) inputManagerF.systemRunning();} catch (Throwable e) {reportWtf("Notifying InputManagerService running", e);}try {if (telephonyRegistryF != null) telephonyRegistryF.systemRunning();} catch (Throwable e) {reportWtf("Notifying TelephonyRegistry running", e);}try {if (mediaRouterF != null) mediaRouterF.systemRunning();} catch (Throwable e) {reportWtf("Notifying MediaRouterService running", e);}try {if (mmsServiceF != null) mmsServiceF.systemRunning();} catch (Throwable e) {reportWtf("Notifying MmsService running", e);}try {if (networkScoreF != null) networkScoreF.systemRunning();} catch (Throwable e) {reportWtf("Notifying NetworkScoreService running", e);}Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);}});

从注释我们可以看出，在这里会进行调起Launcher的动作，点击进入SystemReady这个函数的细节，从而进入了ActivityManagerService.java,该类位于/framework/base/services/core/java/com/android/server/am/下，完整的systemReady函数代码如下：

public void systemReady(final Runnable goingCallback) {synchronized(this) {if (mSystemReady) {// If we're done calling all the receivers, run the next "boot phase" passed in// by the SystemServerif (goingCallback != null) {goingCallback.run();}return;}mLocalDeviceIdleController= LocalServices.getService(DeviceIdleController.LocalService.class);// Make sure we have the current profile info, since it is needed for security checks.mUserController.onSystemReady();mRecentTasks.onSystemReadyLocked();mAppOpsService.systemReady();mSystemReady = true;}ArrayList<ProcessRecord> procsToKill = null;synchronized(mPidsSelfLocked) {for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {ProcessRecord proc = mPidsSelfLocked.valueAt(i);if (!isAllowedWhileBooting(proc.info)){if (procsToKill == null) {procsToKill = new ArrayList<ProcessRecord>();}procsToKill.add(proc);}}}synchronized(this) {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);removeProcessLocked(proc, true, false, "system update done");}}// 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());synchronized(this) {// Make sure we have no pre-ready processes sitting around.if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL) {ResolveInfo ri = mContext.getPackageManager().resolveActivity(new Intent(Intent.ACTION_FACTORY_TEST),STOCK_PM_FLAGS);CharSequence errorMsg = null;if (ri != null) {ActivityInfo ai = ri.activityInfo;ApplicationInfo app = ai.applicationInfo;if ((app.flags&ApplicationInfo.FLAG_SYSTEM) != 0) {mTopAction = Intent.ACTION_FACTORY_TEST;mTopData = null;mTopComponent = new ComponentName(app.packageName,ai.name);} else {errorMsg = mContext.getResources().getText(com.android.internal.R.string.factorytest_not_system);}} else {errorMsg = mContext.getResources().getText(com.android.internal.R.string.factorytest_no_action);}if (errorMsg != null) {mTopAction = null;mTopData = null;mTopComponent = null;Message msg = Message.obtain();msg.what = SHOW_FACTORY_ERROR_UI_MSG;msg.getData().putCharSequence("msg", errorMsg);mUiHandler.sendMessage(msg);}}}retrieveSettings();final int currentUserId;synchronized (this) {currentUserId = mUserController.getCurrentUserIdLocked();readGrantedUriPermissionsLocked();}if (goingCallback != null) goingCallback.run();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 appsstartPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);// Start up initial activity.mBooting = true;// Enable home activity for system user, so that the system can always bootif (UserManager.isSplitSystemUser()) {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();}}startHomeActivityLocked(currentUserId, "systemReady");try {if (AppGlobals.getPackageManager().hasSystemUidErrors()) {Slog.e(TAG, "UIDs on the system are inconsistent, you need to wipe your"+ " data partition or your device will be unstable.");mUiHandler.obtainMessage(SHOW_UID_ERROR_UI_MSG).sendToTarget();}} catch (RemoteException e) {}if (!Build.isBuildConsistent()) {Slog.e(TAG, "Build fingerprint is not consistent, warning user");mUiHandler.obtainMessage(SHOW_FINGERPRINT_ERROR_UI_MSG).sendToTarget();}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, AppOpsManager.OP_NONE,null, false, false, MY_PID, Process.SYSTEM_UID,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() {@Overridepublic 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}, AppOpsManager.OP_NONE,null, true, false, MY_PID, Process.SYSTEM_UID, UserHandle.USER_ALL);} catch (Throwable t) {Slog.wtf(TAG, "Failed sending first user broadcasts", t);} finally {Binder.restoreCallingIdentity(ident);}mStackSupervisor.resumeFocusedStackTopActivityLocked();mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId);}}

从上面我们可以看出，在这部分代码完成后，会回调传入的Runnable接口，仔细察看这段代码，我们看到startHomeActivityLocked(currentUserId, "systemReady");这样一个函数，从函数名可以看出，在这里其调起了系统的Launcher，跳入函数内部，查看代码细节：

boolean startHomeActivityLocked(int userId, String reason) {if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL&& mTopAction == null) {// We are running in factory test mode, but unable to find// the factory test app, so just sit around displaying the// error message and don't try to start anything.return false;}Intent intent = getHomeIntent();ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);if (aInfo != null) {intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));// Don't do this if the home app is currently being// instrumented.aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);ProcessRecord app = getProcessRecordLocked(aInfo.processName,aInfo.applicationInfo.uid, true);if (app == null || app.instrumentationClass == null) {intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);}} else {Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());}return true;}

boolean startHomeActivityLocked(int userId, String reason) {if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL&& mTopAction == null) {// We are running in factory test mode, but unable to find// the factory test app, so just sit around displaying the// error message and don't try to start anything.return false;}Intent intent = getHomeIntent();ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);if (aInfo != null) {intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));// Don't do this if the home app is currently being// instrumented.aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);ProcessRecord app = getProcessRecordLocked(aInfo.processName,aInfo.applicationInfo.uid, true);if (app == null || app.instrumentationClass == null) {intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);}} else {Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());}return true;}

Intent getHomeIntent() {Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);intent.setComponent(mTopComponent);intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {intent.addCategory(Intent.CATEGORY_HOME);}return intent;}