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

(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。