Service启动流程源码分析（一）：startService

Service启动流程源码分析（一）：startService

Service是Android组件中最基本也是最为常见用的四大组件之一，分析Service启动流程源码可以加深对Service的了解。Service一共有两种状态，启动和绑定，本文先分析Service启动的流程，大体上和之前的Activity启动流程类似。

Service启动流程源码分析（二）：bindService

启动流程

1.多次调用怎么执行 2.执行的线程 3.startService也有注释 分析一下 所有博客都有这几个问题

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Activity

本文从Activity的startService(Intent service)入手分析

• Activity的startService(Intent service)代码如下

@Override    public ComponentName startService(Intent service) {        // mBase在之前Activity启动流程中分析过，是在Activity的attach方法中赋值的，是一个ContextImpl        return mBase.startService(service);    }

• 调用ContextImpl的startService(service)，代码如下

@Override    public ComponentName startService(Intent service) {        warnIfCallingFromSystemProcess();        return startServiceCommon(service, mUser);    }

• 调用ContextImpl的startServiceCommon(Intent service, UserHandle user)，代码如下

private ComponentName startServiceCommon(Intent service, UserHandle user) {        try {            // Android 5.0之后不允许隐式启动Service            validateServiceIntent(service);            // Binder调用ActivityManagerNative.getDefault()启动Service，同Activity的启动            ComponentName cn = ActivityManagerNative.getDefault().startService(                mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(                            getContentResolver()), getOpPackageName(), user.getIdentifier());            ...            return cn;        } catch (RemoteException e) {            throw e.rethrowFromSystemServer();        }    }

• Android 5.0之后不允许隐式启动Service，个人觉得Google是为了安全考虑，限制代码如下

private void validateServiceIntent(Intent service) {        // 5.0以上启动Service时切记要设置相关内容        if (service.getComponent() == null && service.getPackage() == null) {            if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {                IllegalArgumentException ex = new IllegalArgumentException(                        "Service Intent must be explicit: " + service);                throw ex;            } else {                Log.w(TAG, "Implicit intents with startService are not safe: " + service                        + " " + Debug.getCallers(2, 3));            }        }    }

ActivityManagerService

public abstract class ActivityManagerNative extends Binder implements IActivityManager
public interface IActivityManager extends IInterface
从中可以看出ActivityManagerNative是一个Binder类，Service的启动已经通过Binder调用转交到系统服务中了。
IActivityManager Binder具体实现是ActivityManagerService，最终调用到ActivityManagerService的startService
调用进入ActivityManagerService的进程

• ActivityManagerService的startService(IApplicationThread caller, Intent service,
  String resolvedType, String callingPackage, int userId)是一次Binder调用，代码如下

 @Override    public ComponentName startService(IApplicationThread caller, Intent service,            String resolvedType, String callingPackage, int userId)            throws TransactionTooLargeException {        ...        synchronized(this) {             ...            // mServices是一个ActiveServices            ComponentName res = mServices.startServiceLocked(caller, service,                    resolvedType, callingPid, callingUid, callingPackage, userId);            return res;        }    }

ActiveServices

ActiveServices是AMS中专门抽出来管理Service活动的类，包括启动、绑定等。

• ActiveServices的startServiceLocked调用了startServiceInnerLocked
• startServiceInnerLocked调用了bringUpServiceLocked
• bringUpServiceLocked调用了realStartServiceLocked
• realStartServiceLocked代码如下

private final void realStartServiceLocked(ServiceRecord r,            ProcessRecord app, boolean execInFg) throws RemoteException {        ...        try {            ...            // 第一步，主要就是通过app.thread（ApplicationThread）Binder调用scheduleCreateService启动Service            app.thread.scheduleCreateService(r, r.serviceInfo,                    mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),                    app.repProcState);         ...        }         // 第二步，sendServiceArgsLocked调用了ApplicationThread的scheduleServiceArgs方法        sendServiceArgsLocked(r, execInFg, true);        ...    }

ApplicationThread

IApplicationThread thread;
public interface IApplicationThread extends IInterface
public abstract class ApplicationThreadNative extends Binder implements IApplicationThread
ApplicationThreadNative的具体实现是ActivityThread中的ApplicationThread
ApplicationThread实现了许多Activity和Service 启动、暂停等有关的操作
调用进入应用程序的进程

• 第一步，调用ApplicationThread的scheduleCreateService，是一次Binder调用

 public final void scheduleCreateService(IBinder token,                ServiceInfo info, CompatibilityInfo compatInfo, int processState) {            ...            // 类似Activity启动，通过mH发送一条CREATE_SERVICE消息            sendMessage(H.CREATE_SERVICE, s);        }

• mH收到H.CREATE_SERVICE，调用handleCreateService(CreateServiceData data)，代码如下

private void handleCreateService(CreateServiceData data) {        LoadedApk packageInfo = getPackageInfoNoCheck(                data.info.applicationInfo, data.compatInfo);        Service service = null;        try {            // 实例化Service            java.lang.ClassLoader cl = packageInfo.getClassLoader();            service = (Service) cl.loadClass(data.info.name).newInstance();        }         try {            // 创建ContextImpl            ContextImpl context = ContextImpl.createAppContext(this, packageInfo);            // 尝试创建Application            Application app = packageInfo.makeApplication(false, mInstrumentation);            // 将之前创建的ContextImpl给service的mBase赋值            service.attach(context, this, data.info.name, data.token, app,                    ActivityManagerNative.getDefault());            // 调用Service的onCreate方法            service.onCreate();            // 将service对象保存在ActivityThread中            //     final ArrayMap<IBinder, Service> mServices = new ArrayMap<>();            mServices.put(data.token, service);            try {// 调用AMS的serviceDoneExecutingActivityManagerNative.getDefault().serviceDoneExecuting(                        data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);            }            ...        }     }

• 第二步，调用ApplicationThread的scheduleServiceArgs，是一次Binder调用
• scheduleServiceArgs类似scheduleCreateService，通过mH发送H.SERVICE_ARGS，mH收到消息调用handleServiceArgs(ServiceArgsData data)，代码如下

private void handleServiceArgs(ServiceArgsData data) {        Service s = mServices.get(data.token);        if (s != null) {            try {                if (!data.taskRemoved) {                    // 调用Service的onStartCommand方法                    res = s.onStartCommand(data.args, data.flags, data.startId);                }...        }        ...    }

• handleServiceArgs最终调用了Service的onStartCommand方法

总结

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流程图待补充

Service启动流程源码分析（二）：bindService