Java layer related service analysis - based on Android 12 S code analysis

frameworks/base/services/java/com/android/server/SystemServer.java

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

 private void run() {
...
        Looper.prepareMainLooper();
        Looper.getMainLooper().setSlowLogThresholdMs(
               SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);

        // Start services.
        try {
            t.traceBegin("StartServices");
            startBootstrapServices(t);
            startCoreServices(t);
            startOtherServices(t);
        } catch (Throwable ex) {
            Slog.e("System", "******************************************");
            Slog.e("System", "************ Failure starting system services", ex);
            throw ex;
        } finally {
            t.traceEnd(); // StartServices
        }
...
        // Loop forever.
        Looper.loop();
        throw new RuntimeException("Main thread loop unexpectedly exited");
 }

    /**
     * Starts the small tangle of critical services that are needed to get the system off the
     * ground.  These services have complex mutual dependencies which is why we initialize them all
     * in one place here.  Unless your service is also entwined in these dependencies, it should be
     * initialized in one of the other functions.
     */
    private void startBootstrapServices(@NonNull TimingsTraceAndSlog t) {
        t.traceBegin("startBootstrapServices");
...
        // Activity manager runs the show.
        t.traceBegin("StartActivityManager");
        // TODO: Might need to move after migration to WM.
        ActivityTaskManagerService atm = mSystemServiceManager.startService(
                ActivityTaskManagerService.Lifecycle.class).getService();
        mActivityManagerService = ActivityManagerService.Lifecycle.startService(
                mSystemServiceManager, atm);
        mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
        mActivityManagerService.setInstaller(installer);
        mWindowManagerGlobalLock = atm.getGlobalLock();
        t.traceEnd();
...
        // Set up the Application instance for the system process and get started.
        t.traceBegin("SetSystemProcess");
        mActivityManagerService.setSystemProcess();
        t.traceEnd();
...
 }

    /**
     * Starts a miscellaneous grab bag of stuff that has yet to be refactored and organized.
     */
    private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
        t.traceBegin("startOtherServices");
...
            t.traceBegin("StartInputManagerService");
            inputManager = new InputManagerService(context);
            t.traceEnd();
...
            t.traceBegin("StartWindowManagerService");
            // WMS needs sensor service ready
            mSystemServiceManager.startBootPhase(t, SystemService.PHASE_WAIT_FOR_SENSOR_SERVICE);
            wm = WindowManagerService.main(context, inputManager, !mFirstBoot, mOnlyCore,
                    new PhoneWindowManager(), mActivityManagerService.mActivityTaskManager);
            ServiceManager.addService(Context.WINDOW_SERVICE, wm, /* allowIsolated= */ false,
                    DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PROTO);
            ServiceManager.addService(Context.INPUT_SERVICE, inputManager,
                    /* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
            t.traceEnd();

            t.traceBegin("SetWindowManagerService");
            mActivityManagerService.setWindowManager(wm);
            t.traceEnd();

            t.traceBegin("WindowManagerServiceOnInitReady");
            wm.onInitReady();
            t.traceEnd();
 }

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
    public void setSystemProcess() {
        try {
//将ActivityManagerService添加进ServiceManager
            ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
                    DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
            ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
            ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
                    DUMP_FLAG_PRIORITY_HIGH);
            ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
            ServiceManager.addService("dbinfo", new DbBinder(this));
            mAppProfiler.setCpuInfoService();
            ServiceManager.addService("permission", new PermissionController(this));
            ServiceManager.addService("processinfo", new ProcessInfoService(this));
            ServiceManager.addService("cacheinfo", new CacheBinder(this));
...
    }
frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java
    public static WindowManagerService main(final Context context, final InputManagerService im,
            final boolean showBootMsgs, final boolean onlyCore, WindowManagerPolicy policy,
            ActivityTaskManagerService atm) {
        return main(context, im, showBootMsgs, onlyCore, policy, atm,
                new DisplayWindowSettingsProvider(), SurfaceControl.Transaction::new, Surface::new,
                SurfaceControl.Builder::new);
    }

    /**
     * Creates and returns an instance of the WindowManagerService. This call allows the caller
     * to override factories that can be used to stub native calls during test.
     */
    @VisibleForTesting
    public static WindowManagerService main(final Context context, final InputManagerService im,
            final boolean showBootMsgs, final boolean onlyCore, WindowManagerPolicy policy,
            ActivityTaskManagerService atm, DisplayWindowSettingsProvider
            displayWindowSettingsProvider, Supplier<SurfaceControl.Transaction> transactionFactory,
            Supplier<Surface> surfaceFactory,
            Function<SurfaceSession, SurfaceControl.Builder> surfaceControlFactory) {
        DisplayThread.getHandler().runWithScissors(() ->
                sInstance = new WindowManagerService(context, im, showBootMsgs, onlyCore, policy,
                        atm, displayWindowSettingsProvider, transactionFactory, surfaceFactory,
                        surfaceControlFactory), 0);
        return sInstance;
    }
frameworks/base/services/core/java/com/android/server/DisplayThread.java
public final class DisplayThread extends ServiceThread {
    private static void ensureThreadLocked() {
        if (sInstance == null) {
            sInstance = new DisplayThread();
            sInstance.start();
            sInstance.getLooper().setTraceTag(Trace.TRACE_TAG_SYSTEM_SERVER);
            sHandler = new Handler(sInstance.getLooper());
        }
    }
    public static Handler getHandler() {
        synchronized (DisplayThread.class) {
            ensureThreadLocked();
            return sHandler;
        }
    }
}
frameworks/base/core/java/android/os/Handler.java
public class Handler {
    public final boolean runWithScissors(@NonNull Runnable r, long timeout) {
        if (r == null) {
            throw new IllegalArgumentException("runnable must not be null");
        }
        if (timeout < 0) {
            throw new IllegalArgumentException("timeout must be non-negative");
        }

        if (Looper.myLooper() == mLooper) {
            r.run();
            return true;
        }

        BlockingRunnable br = new BlockingRunnable(r);
        return br.postAndWait(this, timeout);
    }
}

 It can be seen that the process numbers of services such as WindowManagerService and ActivityManagerService are SystemServer, but they run on different threads.