菜鸟学Android源码－System Server服务启动(Launcher调起)
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(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.cpp if (!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/11463182 SystemProperties.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() { @Override public 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_server BinderInternal.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() { @Override public 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 manager if (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 SystemServer if (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 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 if (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() { @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}, 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; }从上面这三个函数，我们可以看出其最终是走入同路径下的ActivityStarter.java，以Intent的形式调起了系统默认的Launcher应用。
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