Android Launcher启动流程

快来打我* 2023-10-11 09:24 40阅读 0赞

Launcher App 由SystemServer启动，而SystemServer由Zygote进程孵化出来的。

> Zygote是孵化器，所有其他Dalvik/ART虚拟机进程都是用过zygote孵化(fock)出来的  
> SystemServer进程是Android系统的核心之一，大部分Android提供的服务都在该进程中，主要包括ActivityManagerService(AMS)、WindowManagerService(WMS)、PackageManagerSerice(PMS)等。

来看zygote-> SystemServer 入口：  
位于`frameworks/base/services/java/com/android/server/SystemServer.java`

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

可以看到，这里main方法调用了run方法

private void run() {
        
    	//...
    	// Start services.
        traceBeginAndSlog("StartServices");
        startBootstrapServices(); //启动引导服务
        startCoreServices(); //启动核心服务
        startOtherServices(); //启动其他服务
        //...
    }

来看startOtherServices，主要来看SystemServer的systemReady方法，这是Launcher启动的唯一入口。这个方法的作用是只有AMS启动完毕后，才会去回调Runnable中的代码。

private void startOtherServices(){
        
    	//...
    	mActivityManagerService.systemReady(() -> {
        
    		//只有ActivityManagerService启动完之后，才会去启动回调里的这些服务
    	    Slog.i(TAG, "Making services ready");
    	    mSystemServiceManager.startBootPhase(
    	            SystemService.PHASE_ACTIVITY_MANAGER_READY);
    	    //...
        }
        //...
    }

来看`ActivityManagerService.systemReady()`

public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
        
    	//...
    	mStackSupervisor.resumeFocusedStackTopActivityLocked();
    	//...
    }

再来看`ActivityStackSupervisor.resumeFocusedStackTopActivityLocked`

boolean resumeFocusedStackTopActivityLocked(
                ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
        
    	//...
        final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
        if (r == null || r.state != RESUMED) {
        
            mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
        } else if (r.state == RESUMED) {
        
            mFocusedStack.executeAppTransition(targetOptions);
        }
    
        return false;
    }

再来看`ActivityStack.resumeTopActivityUncheckedLocked`

boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        
            //...
            boolean result = false;
            try {
        
                mStackSupervisor.inResumeTopActivity = true;
                result = resumeTopActivityInnerLocked(prev, options);
            } finally {
        
                mStackSupervisor.inResumeTopActivity = false;
            }
    		//...
            return result;
        }

再来看`resumeTopActivityInnerLocked`

private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
        
         //...
         if (!hasRunningActivity) {
        
             return resumeTopActivityInNextFocusableStack(prev, options, "noMoreActivities");
         }
         //...
    }

接着来看`resumeTopActivityInNextFocusableStack`

private boolean resumeTopActivityInNextFocusableStack(ActivityRecord prev,
                ActivityOptions options, String reason) {
        
    	//...
    	// Only resume home if on home display
     	return isOnHomeDisplay() &&
              mStackSupervisor.resumeHomeStackTask(prev, reason);
    }

这里的`mStackSupervisor.resumeHomeStackTask`就是真正启动Launcher App的入口了

boolean resumeHomeStackTask(ActivityRecord prev, String reason) {
        
        //...
        return mService.startHomeActivityLocked(mCurrentUser, myReason);
    }

这里会通过ActivityManagerService.startHomeActivityLocked

来看ActivityManagerService

boolean startHomeActivityLocked(int userId, String reason) {
        
            //...
            Intent intent = getHomeIntent();
            ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
            if (aInfo != null) {
        
            	//创建Launcher启动所需的Intent
                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.instr == null) {
        
                    intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
                    final int resolvedUserId = UserHandle.getUserId(aInfo.applicationInfo.uid);
                    // For ANR debugging to verify if the user activity is the one that actually
                    // launched.
                    final String myReason = reason + ":" + userId + ":" + resolvedUserId;
                    //启动Launcher
                    mActivityStarter.startHomeActivityLocked(intent, aInfo, myReason);
                }
            } else {
        
                Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());
            }
    
            return true;
        }

可以看到，这里通过Intent，调用`mActivityStarter.startHomeActivityLocked`

来看ActivityStarter

void startHomeActivityLocked(Intent intent, ActivityInfo aInfo, String reason) {
        
    		//将Launcher放入HomeStack中，HomeStack是在ActivityManagerService中定义的用于存储Launcher的变量
            mSupervisor.moveHomeStackTaskToTop(reason);
            mLastHomeActivityStartResult = startActivityLocked(null /*caller*/, intent,
                    null /*ephemeralIntent*/, null /*resolvedType*/, aInfo, null /*rInfo*/,
                    null /*voiceSession*/, null /*voiceInteractor*/, null /*resultTo*/,
                    null /*resultWho*/, 0 /*requestCode*/, 0 /*callingPid*/, 0 /*callingUid*/,
                    null /*callingPackage*/, 0 /*realCallingPid*/, 0 /*realCallingUid*/,
                    0 /*startFlags*/, null /*options*/, false /*ignoreTargetSecurity*/,
                    false /*componentSpecified*/, mLastHomeActivityStartRecord /*outActivity*/,
                    null /*inTask*/, "startHomeActivity: " + reason);
            if (mSupervisor.inResumeTopActivity) {
        
                // 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();
            }
        }

在这里就会去Manifest中寻找Launcher应用，并启动Launcher应用，接下来的启动过程就和Activity的启动过程类似了。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0V0aGFuQ28_size_16_color_FFFFFF_t_70]

##### 其他 #####

参考  
[Zygote进程浅析][Zygote]  
[SystemServer进程浅析][SystemServer]  
[Init进程源码分析][Init]  
[开机SystemServer到ActivityManagerService启动过程分析][SystemServer_ActivityManagerService]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0V0aGFuQ28_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2019092214263525.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0V0aGFuQ28=,size_16,color_FFFFFF,t_70
[Zygote]: https://blog.csdn.net/fengluoye2012/article/details/80023051
[SystemServer]: https://blog.csdn.net/fengluoye2012/article/details/80170422
[Init]: https://blog.csdn.net/wangzaieee/article/details/84774298
[SystemServer_ActivityManagerService]: https://www.cnblogs.com/bastard/p/5770573.html