SurfaceComposerClient与SurfaceFlinger建立通信流程

  前面我们已经分析了activity从创建到调用本地方法去创建SurfaceComposerClient的过程。在本文中，我们将详细分析SurfaceComposerClient创建时是如何绑定SurfaceFlinger。

1、申请SurfaceComposerClient入口

[-> android_view_SurfaceSession.cpp]

static jlong nativeCreate(JNIEnv* env, jclass clazz) {
    SurfaceComposerClient* client = new SurfaceComposerClient();//见第二小节
    client->incStrong((void*)nativeCreate);
    return reinterpret_cast<jlong>(client);
}

2、SurfaceComposerClient创建

[-> SurfaceComposerClient.cpp]
SurfaceComposerClient构造函数实现如下：

SurfaceComposerClient::SurfaceComposerClient()
    : mStatus(NO_INIT), mComposer(Composer::getInstance())
{
}

  若是第一次执行会执行onFirstRef方法

void SurfaceComposerClient::onFirstRef() {
    sp<ISurfaceComposer> sm(ComposerService::getComposerService());//见第2.1节
    if (sm != 0) {
        sp<ISurfaceComposerClient> conn = sm->createConnection();//见第2.2节
        if (conn != 0) {
            mClient = conn;
            mStatus = NO_ERROR;
        }
    }
}

2.1 获取surfaceflinger的IBinder

sp<ISurfaceComposer> ComposerService::getComposerService() {
    ComposerService& instance = ComposerService::getInstance();
    Mutex::Autolock _l(instance.mLock);
    if (instance.mComposerService == NULL) {
        ComposerService::getInstance().connectLocked();//见2.1.1节
        assert(instance.mComposerService != NULL);
        ALOGD("ComposerService reconnected");
    }
    return instance.mComposerService;
}

  ComposerService是单例模式，上述方法的作用是，若ComposerService已经创建则直接返回，若没有创建，则创建并执行connectLocked方法。

2.1.1 查找surfaceflinger服务

  在链接过程中，主要做了两件事情：
    1、获取对应的服务
    2、创建死亡监督者并绑定

void ComposerService::connectLocked() {
    const String16 name("SurfaceFlinger");//按名称查找服务
    while (getService(name, &mComposerService) != NO_ERROR) {//见2.1.2节
        usleep(250000);
    }
    assert(mComposerService != NULL);

    // Create the death listener.
    class DeathObserver : public IBinder::DeathRecipient {//死亡监督类
        ComposerService& mComposerService;
        virtual void binderDied(const wp<IBinder>& who) {
            ALOGW("ComposerService remote (surfaceflinger) died [%p]",
                  who.unsafe_get());
            mComposerService.composerServiceDied();
        }
     public:
        DeathObserver(ComposerService& mgr) : mComposerService(mgr) { }
    };

    mDeathObserver = new DeathObserver(*const_cast<ComposerService*>(this));//创建死亡监督对象
    IInterface::asBinder(mComposerService)->linkToDeath(mDeathObserver);//链接死亡监督对象
}

2.1.2 链接surfaceflinger

  getService是一个模板函数，通过参数name去查找获取对应的服务，并将服务的IBinder转化为接口对象输出

template<typename INTERFACE>
status_t getService(const String16& name, sp<INTERFACE>* outService)
{
    const sp<IServiceManager> sm = defaultServiceManager();//服务管理者
    if (sm != NULL) {
    //获取SurfaceFlinger的IBinder，并强转为ISurfaceComposer
        *outService = interface_cast<INTERFACE>(sm->getService(name));
        if ((*outService) != NULL) return NO_ERROR;
    }
    return NAME_NOT_FOUND;
}

2.2 通过链接在surfaceFlinger中创建客户端

  通过ISurfaceComposer的接口createConnection在surfaceFlinger本地创建对应的client对象，用于与应用对应。

2.2.1 Binder通信

  代理端实现如下：

    virtual sp<ISurfaceComposerClient> createConnection()
    {
        Parcel data, reply;
        data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
        remote()->transact(BnSurfaceComposer::CREATE_CONNECTION, data, &reply);//Binder远程调用
        return interface_cast<ISurfaceComposerClient>(reply.readStrongBinder());
    }

  远程服务端实现如下：

status_t BnSurfaceComposer::onTransact(
    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
    switch(code) {
        case CREATE_CONNECTION: {
            CHECK_INTERFACE(ISurfaceComposer, data, reply);
            sp<IBinder> b = IInterface::asBinder(createConnection());//在服务端surfaceFlinger实现
            reply->writeStrongBinder(b);
            return NO_ERROR;
        }
        。。。。。。
}

2.2.2 surfaceFlinger服务端接口实现

  到此，应用端就获取到surfaceFlinger本地client对象，而ISurfaceComposerClient则是应用与client的通信桥梁

sp<ISurfaceComposerClient> SurfaceFlinger::createConnection()
{
    sp<ISurfaceComposerClient> bclient;
    sp<Client> client(new Client(this));//在服务本地创建client与应用对应
    status_t err = client->initCheck();
    if (err == NO_ERROR) {
        bclient = client;
    }
    return bclient;//返回client接口的IBinder
}

3、总结

  未完待续。。。。。。