Service启动流程分析

Service启动流程分析

Service作为Android的四大组件之一非常重要，比起一些后台执行的子线程、异步任务，Service更强大可靠。Service的启动方式有两种一种是直接start启动一个Service，另一种是bind方式绑定一个Service启动。IntentService就是Service，启动方式与普通Service无差。Service及IntentService参考《Service及startService、bindService和unbindServic》和《IntentService使用详解》。

1、启动Service

从startService方法开始，Service的主要启动流程如下：

ContextImpl开始

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

通过ActivityManager获取IActivityManager

public static IActivityManager getService() {
        return IActivityManagerSingleton.get();
    }

ActivityManagerService实现上面的AIDL，内有成员变量

ActiveServices mServices

ActiveServices经过调用链：

startServiceLocked->startServiceInnerLocked->bringUpServiceLocked->realStartServiceLocked

...
    app.thread.scheduleCreateService(r, r.serviceInfo,
               mAm.compatibilityInfoForPackage(r.serviceInfo.applicationInfo),
               app.getReportedProcState());

app是传入的ProcessRecord类型，封装了IApplicationThread类型成员变量

IApplicationThread thread;

ActivityThread中的scheduleCreateService方法向mH发送了消息

    handleCreateService(CreateServiceData data)

try {
        java.lang.ClassLoader cl = packageInfo.getClassLoader();
        service = packageInfo.getAppFactory().instantiateService(cl, data.info.name, data.intent);
    }
        ...
        ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
        context.setOuterContext(service);
        Application app = packageInfo.makeApplication(false, mInstrumentation);
        service.attach(context, this, data.info.name, data.token, app,ActivityManager.getService());

2、绑定Service

前半段基本和启动Service一样，但是后面涉及到绑定Service，会有一些状态的保存及更新。内部用Map来记录保存绑定的Service。

bindService开始

boolean bindService(Intent service,ServiceConnection conn,int flags);

ContextWrapper mBase

public boolean bindService(Intent service, ServiceConnection conn,
            int flags) {
        return mBase.bindService(service, conn, flags);
    }

ContextImpl

public boolean bindService(Intent service, ServiceConnection conn, int flags) {
        warnIfCallingFromSystemProcess();
        return bindServiceCommon(service, conn, flags, null, mMainThread.getHandler(), null,
                getUser());
    }

bindServiceCommon(Intent service, ServiceConnection conn, int flags,String instanceName, Handler handler, Executor executor, UserHandle user)方法中

...
    int res = ActivityManager.getService().bindIsolatedService(
                mMainThread.getApplicationThread(), getActivityToken(), service,
                service.resolveTypeIfNeeded(getContentResolver()),
                sd, flags, instanceName, getOpPackageName(), user.getIdentifier());

ActivityManager getService() 4254

public static IActivityManager getService() {
        return IActivityManagerSingleton.get();
    }

IActivityManager.aidl，实现ActivityManagerService

synchronized(this) {
            return mServices.bindServiceLocked(caller, token, service,
                    resolvedType, connection, flags, instanceName, callingPackage, userId);
        }

ActiveServices mServices

bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,String resolvedType, final IServiceConnection connection, int flags,String instanceName, String callingPackage, final int userId)

bumpServiceExecutingLocked(r, execInFg, "bind");
    r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
    r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
            r.app.getReportedProcState());

ServiceRecord

ProcessRecord app

ProcessRecord

IApplicationThread thread

IApplicationThread

ActivityThread  ：  mH

void scheduleBindService(IBinder token, Intent intent,boolean rebind, int processState)

    private void handleBindService(BindServiceData data) 方法中有一个判断，Service是否是重写绑定，这里我们只追踪首次绑定的流程：

ActivityManager.getService().publishService(data.token, data.intent, binder);

ActiveServices mServices 

c.conn.connected(r.name, service, false)

ConnectionRecord

final IServiceConnection conn;  // The client connection.

IServiceConnection.aidl 的实现在LoadedApk中的InnerConnection内部类：

InnerConnection extends IServiceConnection.Stub {...}