cm-14.1 Android系统启动过程分析（四）-Launcher 启动过程

声明

• 前阶段在项目中涉及到了Android系统定制任务，Android系统定制前提要知道Android系统是如何启动的。
• 本文参考了一些书籍的若干章节，比如《Android进阶解密-第2章-Android系统启动》、《深入理解Android虚拟机-第8/9/10章-init进程详解/Dalvik VM的进程系统/Dalvik VM运作流程详解》、《深入理解Android系统-第6/7/8章-init启动进程详解/Zygote进程详解/System进程详解》等。
• 本文使用的代码是LineageOS的cm-14.1，对应Android 7.1.2，可以参考我的另一篇博客：如何下载Nexus5的LineageOS14.1(cm-14.1)系统源码并编译、刷机。
• 很多代码注释待详细写

0 写在前面的

    等本章结束，Android系统的启动基本就结束了，因为对于用户来说可以看到显示屏上的Launcher界面就代表系统已经启动完成了。Launcher在启动过程中会请求 PackageManagerService 返回系统中已经安装的应用程序的信息，并将这些信息封装成一个快捷图标列表显示在系统屏幕上，这样用户可以通过点击这些快捷图标来启动相应的应用程序。

    Launcher 就是 Android 系统的桌面，它的作用主要有以下两点：

1. 用于启动应用程序。
2. 用于显示和管理应用程序的快捷图标或者其他桌面组件。

0 Launcher启动过程

    SystemServer 进程在启动的过程中会启动PackageManagerService, PackageManagerService 启动后会将系统中的预置的应用程序安装（其中就包含Launcher应用），然后系统服务 AMS 会将 Launcher 启动起来。

...... SystemServer AMS ActivityStackSupervisor ActivityStack startOtherServices systemReady resumeFocusedStack resumeTopActivity... resumeTopActivityInnerLocked resumeHomeStackTask startHomeActivityLocked ...... SystemServer AMS ActivityStackSupervisor ActivityStack

    启动Launcher的入口为AMS的systemReady方法，它在SystemServer的startOtherServices 方告中被调用。其在源码目录：~/LineageOS/frameworks/base/services/java/com/android/server/SystemServer.java

        // 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);
            }
        });
    }

下面来查看 AMS systernReady 方法做了什么：