深入了解mediaserver-3

6. MediaPlayer如何与MediaPlayerService交互

6.1    MeidaPlayerService根据MediaPlayer的请求，创建对应的MeidaPlayer

 //MediaPlayerService.cpp
 static sp<MediaPlayerBase> createPlayer(player_type playerType, void* cookie,
         notify_callback_f notifyFunc)
 {
     sp<MediaPlayerBase> p;
     switch (playerType) {
         case XX_PLAYER:
             LOGV("Create XXPlayer");
             p = new XXPlayerService();
             break;
 #ifndef NO_OPENCORE
         case PV_PLAYER:
             LOGV(" create PVPlayer");
             p = new PVPlayer();
             break;
 #endif
         case SONIVOX_PLAYER:
             LOGV(" create MidiFile");
             p = new MidiFile();
             break;
         case VORBIS_PLAYER:
             LOGV(" create VorbisPlayer");
             p = new VorbisPlayer();
             break;
 #if BUILD_WITH_FULL_STAGEFRIGHT
         case STAGEFRIGHT_PLAYER:
             LOGV(" create StagefrightPlayer");
             p = new StagefrightPlayer;
             break;
 #endif
         case TEST_PLAYER:
             LOGV("Create Test Player stub");
             p = new TestPlayerStub();
             break;
     }
     if (p != NULL) {
         if (p->initCheck() == NO_ERROR) {
             p->setNotifyCallback(cookie, notifyFunc);
         } else {
             p.clear();
         }
     }
     if (p == NULL) {
         LOGE("Failed to create player object");
     }
     return p;
 }

 class MediaPlayer : public BnMediaPlayerClient,
                     public virtual IMediaDeathNotifier

 =============================================================
 class IMediaPlayerClient: public IInterface
 {
 public:
     DECLARE_META_INTERFACE(MediaPlayerClient);

     virtual void notify(int msg, int ext1, int ext2) = 0;
 };

 class BnMediaPlayerClient: public BnInterface<IMediaPlayerClient>
 {
 public:
     virtual status_t    onTransact( uint32_t code,
                                     const Parcel& data,
                                     Parcel* reply,
                                     uint32_t flags = 0);
 };
 =============================================================
 class IMediaDeathNotifier: virtual public RefBase
 {
 public:
     IMediaDeathNotifier() { addObitRecipient(this); }
     virtual ~IMediaDeathNotifier() { removeObitRecipient(this); }

     virtual void died() = 0;
     //establish binder interface to MediaPlayerService
     static const sp<IMediaPlayerService>& getMediaPlayerService();

 private:
     IMediaDeathNotifier &operator=(const IMediaDeathNotifier &);
     IMediaDeathNotifier(const IMediaDeathNotifier &);

     static void addObitRecipient(const wp<IMediaDeathNotifier>& recipient);
     static void removeObitRecipient(const wp<IMediaDeathNotifier>& recipient);

     class DeathNotifier: public IBinder::DeathRecipient
     {
     public:
                 DeathNotifier() {}
         virtual ~DeathNotifier();

         virtual void binderDied(const wp<IBinder>& who);
     };

     friend class DeathNotifier;

     static  Mutex                                   sServiceLock;
     static  sp<IMediaPlayerService>                 sMediaPlayerService;
     static  sp<DeathNotifier>                       sDeathNotifier;
     static  SortedVector< wp<IMediaDeathNotifier> > sObitRecipients;
 }

6.2 通过ServiceManager获取BpMediaPlayerService

 const sp<IMediaPlayerService>& IMediaDeathNotifier::getMediaPlayerService()
 {
     LOGV("getMediaPlayerService");
     Mutex::Autolock _l(sServiceLock);
     if (sMediaPlayerService.get() == 0) {
         sp<IServiceManager> sm = defaultServiceManager();
         sp<IBinder> binder;
         do {
             binder = sm->getService(String16("media.player"));
             if (binder != 0) {
                 break;
              }
              LOGW("Media player service not published, waiting...");
              usleep(500000); // 0.5 s
         } while(true);

         if (sDeathNotifier == NULL) {
         sDeathNotifier = new DeathNotifier();
     }
     binder->linkToDeath(sDeathNotifier);

     // sMediaPlayerService中保存的为BpMediaPlayerService

     sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);
     }
     LOGE_IF(sMediaPlayerService == 0, "no media player service!?");
     return sMediaPlayerService;
 }

6.3 获取mPlayer(IMediaPlayer,实质为BpMediaPlayer) 

 status_t MediaPlayer::setDataSource(
         const char *url, const KeyedVector<String8, String8> *headers)
 {
     LOGV("setDataSource(%s)", url);
     status_t err = BAD_VALUE;
     if (url != NULL) {
         //service实质上是BpMediaPlayerService
         const sp<IMediaPlayerService>& service(getMediaPlayerService());

         if (service != 0) {
             // Player实质上是BpMediaPlayer
             sp<IMediaPlayer> player(service->create(getpid(), this, url, headers));
             //把BpMediaPlayer赋值给成员变量mPlayer,如果以前的mPlayer有效，则Disconnect以前的Player
             err = setDataSource(player);
         }
     }
     return err;
 }

BpMediaPlayerService::create (Client端)

 class BpMediaPlayerService: public BpInterface<IMediaPlayerService>
 {
 public:
     BpMediaPlayerService(const sp<IBinder>& impl)
         : BpInterface<IMediaPlayerService>(impl)
     {
     }

     virtual sp<IMediaPlayer> create(
             pid_t pid, const sp<IMediaPlayerClient>& client,
             const char* url, const KeyedVector<String8, String8> *headers) {
         Parcel data, reply;
         data.writeInterfaceToken(IMediaPlayerService::getInterfaceDescriptor());
         data.writeInt32(pid);
         data.writeStrongBinder(client->asBinder());
         data.writeCString(url);

         if (headers == NULL) {
             data.writeInt32(0);
         } else {
             // serialize the headers
             data.writeInt32(headers->size());
             for (size_t i = 0; i < headers->size(); ++i) {
                 data.writeString8(headers->keyAt(i));
                 data.writeString8(headers->valueAt(i));
             }
         }

         remote()->transact(CREATE_URL, data, &reply);  //传递到BnMediaPlayerSerivce执行
         return interface_cast<IMediaPlayer>(reply.readStrongBinder()); //返回BpMediaPlayer
     }
 }

在BnMediaPlayerService处理CREATE_URL(Server端)

 status_t BnMediaPlayerService::onTransact(
     uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
 {
     switch(code) {
         case CREATE_URL: { //收到上面的CREATE_URL并进行处理
             CHECK_INTERFACE(IMediaPlayerService, data, reply);
             pid_t pid = data.readInt32();
             sp<IMediaPlayerClient> client = //实质保存的为BpMediaPlayerClient,用于向MediaPlayer发通知消息，它为Client,MediaPlayer为Sever
                 interface_cast<IMediaPlayerClient>(data.readStrongBinder());
             const char* url = data.readCString();

             KeyedVector<String8, String8> headers;
             int32_t numHeaders = data.readInt32();
             for (int i = 0; i < numHeaders; ++i) {
                 String8 key = data.readString8();
                 String8 value = data.readString8();
                 headers.add(key, value);
             }
             //在BnMediaPlayerService的派生类MediaPlayerService中实现,创建一个Client对象(Client:public BnMediaPlayer)
             sp<IMediaPlayer> player = create(
                     pid, client, url, numHeaders > 0 ? &headers : NULL);

             reply->writeStrongBinder(player->asBinder());
             return NO_ERROR;
         } break;
 }

MediaPlayerService::create才是真正的实现创建IMediaPlayer

 <p>sp<IMediaPlayer> MediaPlayerService::create(
         pid_t pid, const sp<IMediaPlayerClient>& client, const char* url,
         const KeyedVector<String8, String8> *headers)
 {
     int32_t connId = android_atomic_inc(&mNextConnId);</p><p>     //创建一个Clinet,class Client : public BnMediaPlayer，真正实现start, stop, pause, resume...
     sp<Client> c = new Client(this, pid, connId, client);
     LOGV("Create new client(%d) from pid %d, url=%s, connId=%d", connId, pid, url, connId);</p><p>    //分析url，并创建真正的player(demuxer,decoder)
     if (NO_ERROR != c->setDataSource(url, headers))
     {
         c.clear();
         return c;
     }
     wp<Client> w = c;
     Mutex::Autolock lock(mLock);
     mClients.add(w);
     return c;//返回此BnMediaPlayer派生类的对象
 }</p>

MediaPlayerService::Client::setDataSource分析URL类型，然后创建对应的Player

 status_t MediaPlayerService::Client::setDataSource(
         const char *url, const KeyedVector<String8, String8> *headers)
 {
     LOGV("setDataSource(%s)", url);
     if (url == NULL)
         return UNKNOWN_ERROR;

     if (strncmp(url, "content://", 10) == 0) {
         // get a filedescriptor for the content Uri and
         // pass it to the setDataSource(fd) method

         String16 url16(url);
         int fd = android::openContentProviderFile(url16);
         if (fd < 0)
         {
             LOGE("Couldn't open fd for %s", url);
             return UNKNOWN_ERROR;
         }
         setDataSource(fd, 0, 0x7fffffffffLL); // this sets mStatus
         close(fd);
         return mStatus;
     } else {
         //根据url返回对应的player_type,如: PV_PLAYER,STAGEFRIGHT_PLAYER, XX_PLAYER
         player_type playerType = getPlayerType(url);
         LOGV("player type = %d", playerType);

         // create the right type of player,建立真正的AVPlayer
         sp<MediaPlayerBase> p = createPlayer(playerType);
         if (p == NULL) return NO_INIT;

         if (!p->hardwareOutput()) {
             mAudioOutput = new AudioOutput();
             static_cast<MediaPlayerInterface*>(p.get())->setAudioSink(mAudioOutput);
         }

         // now set data source,把URL传递给真正的AVPlayer
         LOGV(" setDataSource");
         mStatus = p->setDataSource(url, headers);
         p->setOutRange( mService->getLeft(), mService->getTop(), mService->getWidth(), mService->getHeight());
         if (mStatus == NO_ERROR) {
             mPlayer = p;
         } else {
             LOGE("  error: %d", mStatus);
         }
         return mStatus;
     }
 }

创建真正的AVPlayer

 sp<MediaPlayerBase> MediaPlayerService::Client::createPlayer(player_type playerType)
 {
     // determine if we have the right player type
     sp<MediaPlayerBase> p = mPlayer;
     LOGV("Enter MediaPlayerService::Client::createPlayer: playerType is %d", playerType);
     if ((p != NULL) && (p->playerType() != playerType)) {
         LOGV("p->playerType() is: %d, , delete player", p->playerType());
         p.clear();
     }
     if (p == NULL) {
         LOGV("Create new player");
         p = android::createPlayer(playerType, this, notify);
     }
     return p;
 }
 static sp<MediaPlayerBase> createPlayer(player_type playerType, void* cookie,
         notify_callback_f notifyFunc)
 {
     sp<MediaPlayerBase> p;
     switch (playerType) {
         case XX_PLAYER:
             LOGV("Create XXPlayer");
             p = new XXPlayerService();
             break;
 #ifndef NO_OPENCORE
         case PV_PLAYER:
             LOGV(" create PVPlayer");
             p = new PVPlayer();
             break;
 #endif
         case SONIVOX_PLAYER:
             LOGV(" create MidiFile");
             p = new MidiFile();
             break;
         case VORBIS_PLAYER:
             LOGV(" create VorbisPlayer");
             p = new VorbisPlayer();
             break;
 #if BUILD_WITH_FULL_STAGEFRIGHT
         case STAGEFRIGHT_PLAYER:
             LOGV(" create StagefrightPlayer");
             p = new StagefrightPlayer;
             break;
 #endif
         case TEST_PLAYER:
             LOGV("Create Test Player stub");
             p = new TestPlayerStub();
             break;
     }
     if (p != NULL) {
         if (p->initCheck() == NO_ERROR) {
             p->setNotifyCallback(cookie, notifyFunc);
         } else {
             p.clear();
         }
     }
     if (p == NULL) {
         LOGE("Failed to create player object");
     }
     return p;
 }

6.4 开始播放MediaPlayer::start

MediaPlayer::mPlayer实质为BpMediaPlayer

MediaPlayerService::Client::mPlayer实质为真正的AVPlayer,如：PVPlayer, XXPlayer

class PVPlayer: public MediaPlayerInterface

class MediaPlayerInterface : public MediaPlayerBase

 

MediaPlayer::start()  -->  mPlayer->start(BpMediaPlayer::start) --> remote()->transact(START, data, &reply)--> BpBinder::transact--> IPCThreadState::self()->transact--> ioctl(写) --> ioctl(读,在IPCThreadState::joinThreadPool中调用) --> BBinder::transact --> BnMediaPlayer::onTransact --> MediaPlayerService::Client::start -->MediaPlayerService::Client::mPlayer->start(PVPlayer->start)