Launcher 的启动

 mActivityManagerService.systemReady(() -> {
            Slog.i(TAG, "Making services ready");
            t.traceBegin("StartActivityManagerReadyPhase");
            mSystemServiceManager.startBootPhase(t, SystemService.PHASE_ACTIVITY_MANAGER_READY);

t.traceBegin("resumeTopActivities");
mAtmInternal.resumeTopActivities(false /* scheduleIdle */);
t.traceEnd();

public class ActivityTaskManagerService extends IActivityTaskManager.Stub {

        @Override
        public void resumeTopActivities(boolean scheduleIdle) {
            synchronized (mGlobalLock) {
                mRootWindowContainer.resumeFocusedStacksTopActivities();
                if (scheduleIdle) {
                    mStackSupervisor.scheduleIdle();
                }
            }
        }

boolean resumeFocusedStacksTopActivities() {
        return resumeFocusedStacksTopActivities(null, null, null);
    }

    boolean resumeFocusedStacksTopActivities(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
 
        if (!mStackSupervisor.readyToResume()) {
            return false;
        }
 
        boolean result = false;
        if (targetStack != null && (targetStack.isTopStackInDisplayArea()
                || getTopDisplayFocusedStack() == targetStack)) {
            result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
 
        for (int displayNdx = getChildCount() - 1; displayNdx >= 0; --displayNdx) {
            boolean resumedOnDisplay = false;
            final DisplayContent display = getChildAt(displayNdx);
            for (int tdaNdx = display.getTaskDisplayAreaCount() - 1; tdaNdx >= 0; --tdaNdx) {
                final TaskDisplayArea taskDisplayArea = display.getTaskDisplayAreaAt(tdaNdx);
                for (int sNdx = taskDisplayArea.getStackCount() - 1; sNdx >= 0; --sNdx) {
                    final ActivityStack stack = taskDisplayArea.getStackAt(sNdx);
                    final ActivityRecord topRunningActivity = stack.topRunningActivity();
                    if (!stack.isFocusableAndVisible() || topRunningActivity == null) {
                        continue;
                    }
                    if (stack == targetStack) {
                        // Simply update the result for targetStack because the targetStack had
                        // already resumed in above. We don't want to resume it again, especially in
                        // some cases, it would cause a second launch failure if app process was
                        // dead.
                        resumedOnDisplay |= result;
                        continue;
                    }
                    if (taskDisplayArea.isTopStack(stack) && topRunningActivity.isState(RESUMED)) {
                        // Kick off any lingering app transitions form the MoveTaskToFront
                        // operation, but only consider the top task and stack on that display.
                        stack.executeAppTransition(targetOptions);
                    } else {
                        resumedOnDisplay |= topRunningActivity.makeActiveIfNeeded(target);
                    }
                }
            }
            if (!resumedOnDisplay) {
                // In cases when there are no valid activities (e.g. device just booted or launcher
                // crashed) it's possible that nothing was resumed on a display. Requesting resume
                // of top activity in focused stack explicitly will make sure that at least home
                // activity is started and resumed, and no recursion occurs.
                final ActivityStack focusedStack = display.getFocusedStack();
                if (focusedStack != null) {
                    result |= focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);
                } else if (targetStack == null) {
                    result |= resumeHomeActivity(null /* prev */, "no-focusable-task",
                            display.getDefaultTaskDisplayArea());
                }
            }
        }
 
        return result;
    }

    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        if (mInResumeTopActivity) {
            // Don't even start recursing.
            return false;
        }
 
        boolean result = false;
        try {
            // Protect against recursion.
            mInResumeTopActivity = true;
            result = resumeTopActivityInnerLocked(prev, options);
 
            // When resuming the top activity, it may be necessary to pause the top activity (for
            // example, returning to the lock screen. We suppress the normal pause logic in
            // {@link #resumeTopActivityUncheckedLocked}, since the top activity is resumed at the
            // end. We call the {@link ActivityStackSupervisor#checkReadyForSleepLocked} again here
            // to ensure any necessary pause logic occurs. In the case where the Activity will be
            // shown regardless of the lock screen, the call to
            // {@link ActivityStackSupervisor#checkReadyForSleepLocked} is skipped.
            final ActivityRecord next = topRunningActivity(true /* focusableOnly */);
            if (next == null || !next.canTurnScreenOn()) {
                checkReadyForSleep();
            }
        } finally {
            mInResumeTopActivity = false;
        }
 
        return result;
    }

if (!hasRunningActivity) {
            // There are no activities left in the stack, let's look somewhere else.
            return resumeNextFocusableActivityWhenStackIsEmpty(prev, options);
        }

mRootWindowContainer.resumeHomeActivity(prev, reason, getDisplayArea());

   boolean resumeHomeActivity(ActivityRecord prev, String reason,
            TaskDisplayArea taskDisplayArea) {
        if (!mService.isBooting() && !mService.isBooted()) {
            // Not ready yet!
            return false;
        }
 
        if (taskDisplayArea == null) {
            taskDisplayArea = getDefaultTaskDisplayArea();
        }
 
        final ActivityRecord r = taskDisplayArea.getHomeActivity();
        final String myReason = reason + " resumeHomeActivity";
 
        // Only resume home activity if isn't finishing.
        if (r != null && !r.finishing) {
            r.moveFocusableActivityToTop(myReason);
            return resumeFocusedStacksTopActivities(r.getRootTask(), prev, null);
        }
        return startHomeOnTaskDisplayArea(mCurrentUser, myReason, taskDisplayArea,
                false /* allowInstrumenting */, false /* fromHomeKey */);
    }

    boolean startHomeOnTaskDisplayArea(int userId, String reason, TaskDisplayArea taskDisplayArea,
            boolean allowInstrumenting, boolean fromHomeKey) {
        // Fallback to top focused display area if the provided one is invalid.
        if (taskDisplayArea == null) {
            final ActivityStack stack = getTopDisplayFocusedStack();
            taskDisplayArea = stack != null ? stack.getDisplayArea()
                    : getDefaultTaskDisplayArea();
        }
 
        Intent homeIntent = null;
        ActivityInfo aInfo = null;
        if (taskDisplayArea == getDefaultTaskDisplayArea()) {
            homeIntent = mService.getHomeIntent();
            aInfo = resolveHomeActivity(userId, homeIntent);
        } else if (shouldPlaceSecondaryHomeOnDisplayArea(taskDisplayArea)) {
            Pair<ActivityInfo, Intent> info = resolveSecondaryHomeActivity(userId, taskDisplayArea);
            aInfo = info.first;
            homeIntent = info.second;
        }
        if (aInfo == null || homeIntent == null) {
            return false;
        }
 
        if (!canStartHomeOnDisplayArea(aInfo, taskDisplayArea, allowInstrumenting)) {
            return false;
        }
 
        // Updates the home component of the intent.
        homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
        homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
        // Updates the extra information of the intent.
        if (fromHomeKey) {
            homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);
            mWindowManager.cancelRecentsAnimation(REORDER_KEEP_IN_PLACE, "startHomeActivity");
        }
        homeIntent.putExtra(WindowManagerPolicy.EXTRA_START_REASON, reason);
 
        // Update the reason for ANR debugging to verify if the user activity is the one that
        // actually launched.
        final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(
                aInfo.applicationInfo.uid) + ":" + taskDisplayArea.getDisplayId();
        mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
                taskDisplayArea);//启动launcher
        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;
    }

mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
                taskDisplayArea);//启动launcher

ActivityStartController getActivityStartController() {
        return mActivityStartController;
    }

void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason,
            TaskDisplayArea taskDisplayArea) {
        final ActivityOptions options = ActivityOptions.makeBasic();
        options.setLaunchWindowingMode(WINDOWING_MODE_FULLSCREEN);
        if (!ActivityRecord.isResolverActivity(aInfo.name)) {
            // The resolver activity shouldn't be put in home stack because when the foreground is
            // standard type activity, the resolver activity should be put on the top of current
            // foreground instead of bring home stack to front.
            options.setLaunchActivityType(ACTIVITY_TYPE_HOME);
        }
        final int displayId = taskDisplayArea.getDisplayId();
        options.setLaunchDisplayId(displayId);
        options.setLaunchTaskDisplayArea(taskDisplayArea.mRemoteToken
                .toWindowContainerToken());
 
        // The home activity will be started later, defer resuming to avoid unneccerary operations
        // (e.g. start home recursively) when creating home stack.
        mSupervisor.beginDeferResume();
        final ActivityStack homeStack;
        try {
            // Make sure home stack exists on display area.
            homeStack = taskDisplayArea.getOrCreateRootHomeTask(ON_TOP);
        } finally {
            mSupervisor.endDeferResume();
        }
 
        mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
                .setOutActivity(tmpOutRecord)
                .setCallingUid(0)
                .setActivityInfo(aInfo)
                .setActivityOptions(options.toBundle())
                .execute();
        mLastHomeActivityStartRecord = tmpOutRecord[0];
        if (homeStack.mInResumeTopActivity) {
            // If we are in resume section already, home activity will be initialized, but not
            // resumed (to avoid recursive resume) and will stay that way until something pokes it
            // again. We need to schedule another resume.
            mSupervisor.scheduleResumeTopActivities();
        }
    }