int main(int argc, char** argv){//FT，就這么簡單？？//獲得一個ProcessState實例sp<ProcessState> proc(ProcessState::self());//得到一個ServiceManager對象  sp<IServiceManager> sm = defaultServiceManager();  MediaPlayerService::instantiate();//初始化MediaPlayerService服務  ProcessState::self()->startThreadPool();//看名字，啟動Process的線程池？  IPCThreadState::self()->joinThreadPool();//將自己加入到剛才的線程池？}

sp<ProcessState> ProcessState::self(){  if (gProcess != NULL) return gProcess;---->第一次進來肯定不走這兒  AutoMutex _l(gProcessMutex);--->鎖保護  if (gProcess == NULL) gProcess = new ProcessState;--->創建一個ProcessState對象return gProcess;--->看見沒，這里返回的是指針，但是函數返回的是sp<xxx>，所以//把sp<xxx>看成是XXX*是可以的}再來看看ProcessState構造函數//這個構造函數看來很重要ProcessState::ProcessState()  : mDriverFD(open_driver())----->Android很多代碼都是這么寫的,稍不留神就沒看見這里調用了一個很重要的函數  , mVMStart(MAP_FAILED)//映射內存的起始地址  , mManagesContexts(false)  , mBinderContextCheckFunc(NULL)  , mBinderContextUserData(NULL)  , mThreadPoolStarted(false)  , mThreadPoolSeq(1){if (mDriverFD >= 0) {//BIDNER_VM_SIZE定義為(1*1024*1024) - (4096 *2) 1M-8K    mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);//這個需要你自己去man mmap的用法了，不過大概意思就是//將fd映射為內存，這樣內存的memcpy等操作就相當于write/read(fd)了  }  ...} //最討厭這種在構造list中添加函數的寫法了，常常疏忽某個變量的初始化是一個函數調用的結果。//open_driver，就是打開/dev/binder這個設備，這個是android在內核中搞的一個專門用于完成//進程間通訊而設置的一個虛擬的設備。BTW，說白了就是內核的提供的一個機制，這個和我們用socket加NET_LINK方式和內核通訊是一個道理。static int open_driver(){  int fd = open("/dev/binder", O_RDWR);//打開/dev/binder  if (fd >= 0) {   ....    size_t maxThreads = 15;    //通過ioctl方式告訴內核，這個fd支持最大線程數是15個。    result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);  }return fd;

sp<IServiceManager> defaultServiceManager(){  if (gDefaultServiceManager != NULL) return gDefaultServiceManager;  //又是一個單例，設計模式中叫 singleton。  {    AutoMutex _l(gDefaultServiceManagerLock);    if (gDefaultServiceManager == NULL) {//真正的gDefaultServiceManager是在這里創建的喔      gDefaultServiceManager = interface_cast<IServiceManager>(        ProcessState::self()->getContextObject(NULL));    }  }  return gDefaultServiceManager;}-----》gDefaultServiceManager = interface_cast<IServiceManager>(        ProcessState::self()->getContextObject(NULL));ProcessState::self，肯定返回的是剛才創建的gProcess，然后調用它的getContextObject，注意，傳進去的是NULL，即0//回到ProcessState類，sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& caller){if (supportsProcesses()) {//該函數根據打開設備是否成功來判斷是否支持process，//在真機上肯定走這個    return getStrongProxyForHandle(0);//注意，這里傳入0  }}----》進入到getStrongProxyForHandle，函數名字怪怪的，經常嚴重阻礙大腦運轉//注意這個參數的命名，handle。搞過windows的應該比較熟悉這個名字，這是對//資源的一種標示，其實說白了就是某個數據結構，保存在數組中，然后handle是它在這個數組中的索引。--->就是這么一個玩意兒sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle){  sp<IBinder> result;  AutoMutex _l(mLock);handle_entry* e = lookupHandleLocked(handle);--》哈哈，果然，從數組中查找對應索引的資源，lookupHandleLocked這個就不說了，內部會返回一個handle_entry 下面是 handle_entry 的結構/*struct handle_entry {        IBinder* binder;--->Binder        RefBase::weakref_type* refs;-->不知道是什么，不影響.      };*/  if (e != NULL) {    IBinder* b = e->binder; -->第一次進來，肯定為空    if (b == NULL || !e->refs->attemptIncWeak(this)) {      b = new BpBinder(handle); --->看見了吧，創建了一個新的BpBinder      e->binder = b;      result = b;    }....  }  return result; 返回剛才創建的BpBinder。}//到這里，是不是有點亂了？對，當人腦分析的函數調用太深的時候，就容易忘記。//我們是從gDefaultServiceManager = interface_cast<IServiceManager>(        ProcessState::self()->getContextObject(NULL));//開始搞的，現在，這個函數調用將變成gDefaultServiceManager = interface_cast<IServiceManager>(new BpBinder(0));

BpBinder::BpBinder(int32_t handle)  : mHandle(handle) //注意，接上述內容，這里調用的時候傳入的是0  , mAlive(1)  , mObitsSent(0)  , mObituaries(NULL){  IPCThreadState::self()->incWeakHandle(handle);//FT，竟然到IPCThreadState::self()}這里一塊說說吧，IPCThreadState::self估計怎么著又是一個singleton吧？//該文件位置在framework/base/libs/binder/IPCThreadState.cppIPCThreadState* IPCThreadState::self(){  if (gHaveTLS) {//第一次進來為falserestart:    const pthread_key_t k = gTLS;//TLS是Thread Local Storage的意思，不懂得自己去google下它的作用吧。這里只需要//知道這種空間每個線程有一個，而且線程間不共享這些空間，好處是？我就不用去搞什么//同步了。在這個線程，我就用這個線程的東西，反正別的線程獲取不到其他線程TLS中的數據。===》這句話有漏洞，鉆牛角尖的明白大概意思就可以了。//從線程本地存儲空間中獲得保存在其中的IPCThreadState對象//這段代碼寫法很晦澀，看見沒，只有pthread_getspecific,那么肯定有地方調用// pthread_setspecific。    IPCThreadState* st = (IPCThreadState*)pthread_getspecific(k);    if (st) return st;    return new IPCThreadState;//new一個對象，  }    if (gShutdown) return NULL;    pthread_mutex_lock(&gTLSMutex);  if (!gHaveTLS) {    if (pthread_key_create(&gTLS, threadDestructor) != 0) {      pthread_mutex_unlock(&gTLSMutex);      return NULL;    }    gHaveTLS = true;  }  pthread_mutex_unlock(&gTLSMutex);goto restart; //我FT，其實goto沒有我們說得那樣卑鄙，匯編代碼很多跳轉語句的。//關鍵是要用好。}//這里是構造函數，在構造函數里邊pthread_setspecificIPCThreadState::IPCThreadState()  : mProcess(ProcessState::self()), mMyThreadId(androidGetTid()){  pthread_setspecific(gTLS, this);  clearCaller();mIn.setDataCapacity(256);//mIn,mOut是兩個Parcel，干嘛用的啊？把它看成是命令的buffer吧。再深入解釋，又會大腦停擺的。  mOut.setDataCapacity(256);}

BpBinder::BpBinder(int32_t handle)  : mHandle(handle) //注意，接上述內容，這里調用的時候傳入的是0  , mAlive(1)  , mObitsSent(0)  , mObituaries(NULL){......IPCThreadState::self()->incWeakHandle(handle);什么incWeakHandle，不講了..}

template<typename INTERFACE>inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj){  return INTERFACE::asInterface(obj);}所以，上面等價于：inline sp<IServiceManager> interface_cast(const sp<IBinder>& obj){  return IServiceManager::asInterface(obj);}看來，只能跟到IServiceManager了。IServiceManager.h---》framework/base/include/binder/IServiceManager.h看看它是如何定義的:

class IServiceManager : public IInterface{//ServiceManager,字面上理解就是Service管理類，管理什么？增加服務，查詢服務等//這里僅列出增加服務addService函數public:  DECLARE_META_INTERFACE(ServiceManager);   virtual status_t  addService( const String16& name,                      const sp<IBinder>& service) = 0;};DECLARE_META_INTERFACE(ServiceManager)？？怎么和MFC這么類似？微軟的影響很大啊！知道MFC的，有DELCARE肯定有IMPLEMENT果然，這兩個宏DECLARE_META_INTERFACE和IMPLEMENT_META_INTERFACE(INTERFACE, NAME)都在剛才的IInterface.h中定義。我們先看看DECLARE_META_INTERFACE這個宏往IServiceManager加了什么？下面是DECLARE宏#define DECLARE_META_INTERFACE(INTERFACE)                /  static const android::String16 descriptor;             /  static android::sp<I##INTERFACE> asInterface(            /      const android::sp<android::IBinder>& obj);         /  virtual const android::String16& getInterfaceDescriptor() const;  /  I##INTERFACE();                           /  virtual ~I##INTERFACE();  我們把它兌現到IServiceManager就是：static const android::String16 descriptor; -->喔，增加一個描述字符串static android::sp< IServiceManager > asInterface(const android::sp<android::IBinder>&obj) ---》增加一個asInterface函數virtual const android::String16& getInterfaceDescriptor() const; ---》增加一個get函數估計其返回值就是descriptor這個字符串IServiceManager ();                           /virtual ~IServiceManager();增加構造和虛析購函數...

IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");下面是這個宏的定義#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME)            /  const android::String16 I##INTERFACE::descriptor(NAME);       /  const android::String16&                      /      I##INTERFACE::getInterfaceDescriptor() const {       /    return I##INTERFACE::descriptor;                /  }                                  /  android::sp<I##INTERFACE> I##INTERFACE::asInterface(        /      const android::sp<android::IBinder>& obj)          /  {                                  /    android::sp<I##INTERFACE> intr;                 /    if (obj != NULL) {                       /      intr = static_cast<I##INTERFACE*>(             /        obj->queryLocalInterface(                /            I##INTERFACE::descriptor).get());        /      if (intr == NULL) {                     /        intr = new Bp##INTERFACE(obj);             /      }                              /    }                                /    return intr;                          /  }                                  /  I##INTERFACE::I##INTERFACE() { }                  /I##INTERFACE::~I##INTERFACE() { }                  /很麻煩吧？尤其是宏看著頭疼。趕緊兌現下吧。constandroid::String16 IServiceManager::descriptor(“android.os.IServiceManager”);const android::String16& IServiceManager::getInterfaceDescriptor() const { return IServiceManager::descriptor;//返回上面那個android.os.IServiceManager  }                                   android::sp<IServiceManager> IServiceManager::asInterface(      const android::sp<android::IBinder>& obj)  {    android::sp<IServiceManager> intr;    if (obj != NULL) {                             intr = static_cast<IServiceManager *>(                     obj->queryLocalInterface(IServiceManager::descriptor).get());             if (intr == NULL) {                             intr = new BpServiceManager(obj);                   }                                 }                                    return intr;                            }                                   IServiceManager::IServiceManager () { }                    IServiceManager::~ IServiceManager() { } 哇塞，asInterface是這么搞的啊，趕緊分析下吧，還是不知道interface_cast怎么把BpBinder*轉成了IServiceManager我們剛才解析過的interface_cast<IServiceManager>(new BpBinder(0)),原來就是調用asInterface(new BpBinder(0))android::sp<IServiceManager> IServiceManager::asInterface(      const android::sp<android::IBinder>& obj)  {    android::sp<IServiceManager> intr;    if (obj != NULL) {                             ....                           intr = new BpServiceManager(obj);//神吶，終于看到和IServiceManager相關的東西了，看來//實際返回的是BpServiceManager(new BpBinder(0))；                   }                                 }                                   return intr;                          }       

class BpServiceManager : public BpInterface<IServiceManager>//這種繼承方式，表示同時繼承BpInterface和IServiceManager，這樣IServiceManger的addService必然在這個類中實現{public://注意構造函數參數的命名 impl，難道這里使用了Bridge模式？真正完成操作的是impl對象？//這里傳入的impl就是new BpBinder(0)  BpServiceManager(const sp<IBinder>& impl)    : BpInterface<IServiceManager>(impl)  {  }   virtual status_t addService(const String16& name, const sp<IBinder>& service)  {    待會再說..}基類BpInterface的構造函數（經過兌現后）//這里的參數又叫remote，唉，真是害人不淺啊。inline BpInterface< IServiceManager >::BpInterface(const sp<IBinder>& remote)  : BpRefBase(remote){}BpRefBase::BpRefBase(const sp<IBinder>& o)  : mRemote(o.get()), mRefs(NULL), mState(0)//o.get()，這個是sp類的獲取實際數據指針的一個方法，你只要知道//它返回的是sp<xxxx>中xxx* 指針就行{//mRemote就是剛才的BpBinder(0)  ...}

int main(int argc, char** argv){  sp<ProcessState> proc(ProcessState::self());sp<IServiceManager> sm = defaultServiceManager();//上面的講解已經完了MediaPlayerService::instantiate();//實例化MediaPlayerservice//看來這里有名堂！   ProcessState::self()->startThreadPool();  IPCThreadState::self()->joinThreadPool();}

void MediaPlayerService::instantiate() {defaultServiceManager()->addService(//傳進去服務的名字，傳進去new出來的對象      String16("media.player"), new MediaPlayerService());}MediaPlayerService::MediaPlayerService(){  LOGV("MediaPlayerService created");//太簡單了  mNextConnId = 1;}defaultServiceManager返回的是剛才創建的BpServiceManager調用它的addService函數。

virtual status_t addService(const String16& name, const sp<IBinder>& service)  {    Parcel data, reply;//data是發送到BnServiceManager的命令包//看見沒？先把Interface名字寫進去，也就是什么android.os.IServiceManager    data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());//再把新service的名字寫進去 叫media.player    data.writeString16(name);//把新服務service―>就是MediaPlayerService寫到命令中    data.writeStrongBinder(service);//調用remote的transact函數    status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);    return err == NO_ERROR ? reply.readInt32() : err;}

BpBinder的位置在framework/base/libs/binder/BpBinder.cppstatus_t BpBinder::transact(  uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){//又繞回去了，調用IPCThreadState的transact。//注意啊，這里的mHandle為0,code是ADD_SERVICE_TRANSACTION,data是命令包//reply是回復包，flags=0    status_t status = IPCThreadState::self()->transact(      mHandle, code, data, reply, flags);    if (status == DEAD_OBJECT) mAlive = 0;    return status;  }...}再看看IPCThreadState的transact函數把status_t IPCThreadState::transact(int32_t handle,                 uint32_t code, const Parcel& data,                 Parcel* reply, uint32_t flags){  status_t err = data.errorCheck();   flags |= TF_ACCEPT_FDS;    if (err == NO_ERROR) {    //調用writeTransactionData 發送數據err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);  }     if ((flags & TF_ONE_WAY) == 0) {    if (reply) {      err = waitForResponse(reply);    } else {      Parcel fakeReply;      err = waitForResponse(&fakeReply);    }   ....等回復    err = waitForResponse(NULL, NULL);  ....    return err;}再進一步，瞧瞧這個...status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,  int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer){  binder_transaction_data tr;   tr.target.handle = handle;  tr.code = code;  tr.flags = binderFlags;    const status_t err = data.errorCheck();  if (err == NO_ERROR) {    tr.data_size = data.ipcDataSize();    tr.data.ptr.buffer = data.ipcData();    tr.offsets_size = data.ipcObjectsCount()*sizeof(size_t);    tr.data.ptr.offsets = data.ipcObjects();  }....上面把命令數據封裝成binder_transaction_data，然后寫到mOut中，mOut是命令的緩沖區，也是一個Parcel  mOut.writeInt32(cmd);  mOut.write(&tr, sizeof(tr));//僅僅寫到了Parcel中，Parcel好像沒和/dev/binder設備有什么關聯啊？恩，那只能在另外一個地方寫到binder設備中去了。難道是在？  return NO_ERROR;}//說對了，就是在waitForResponse中status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult){  int32_t cmd;  int32_t err; while (1) {//talkWithDriver，哈哈，應該是這里了    if ((err=talkWithDriver()) < NO_ERROR) break;    err = mIn.errorCheck();    if (err < NO_ERROR) break;    if (mIn.dataAvail() == 0) continue;    //看見沒？這里開始操作mIn了，看來talkWithDriver中//把mOut發出去，然后從driver中讀到數據放到mIn中了。    cmd = mIn.readInt32();     switch (cmd) {    case BR_TRANSACTION_COMPLETE:      if (!reply && !acquireResult) goto finish;      break;  .....  return err;}status_t IPCThreadState::talkWithDriver(bool doReceive){binder_write_read bwr;  //中間東西太復雜了，不就是把mOut數據和mIn接收數據的處理后賦值給bwr嗎？  status_t err;  do {//用ioctl來讀寫    if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)      err = NO_ERROR;    else      err = -errno; } while (err == -EINTR);//到這里，回復數據就在bwr中了，bmr接收回復數據的buffer就是mIn提供的    if (bwr.read_consumed > 0) {      mIn.setDataSize(bwr.read_consumed);      mIn.setDataPosition(0);    }return NO_ERROR;}

int main(int argc, char** argv){  sp<ProcessState> proc(ProcessState::self());  sp<IServiceManager> sm = defaultServiceManager();  MediaPlayerService::instantiate();---》該函數內部調用addService，把MediaPlayerService信息 add到ServiceManager中  ProcessState::self()->startThreadPool();  IPCThreadState::self()->joinThreadPool();}

int main(int argc, char **argv){  struct binder_state *bs;  void *svcmgr = BINDER_SERVICE_MANAGER;  bs = binder_open(128*1024);//應該是打開binder設備吧？  binder_become_context_manager(bs) //成為manager  svcmgr_handle = svcmgr;  binder_loop(bs, svcmgr_handler);//處理BpServiceManager發過來的命令}看看binder_open是不是和我們猜得一樣？struct binder_state *binder_open(unsigned mapsize){  struct binder_state *bs;  bs = malloc(sizeof(*bs));  ....  bs->fd = open("/dev/binder", O_RDWR);//果然如此 ....  bs->mapsize = mapsize;  bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, 0); }再看看binder_become_context_managerint binder_become_context_manager(struct binder_state *bs){  return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);//把自己設為MANAGER}binder_loop 肯定是從binder設備中讀請求，寫回復的這么一個循環吧？void binder_loop(struct binder_state *bs, binder_handler func){  int res;  struct binder_write_read bwr;  readbuf[0] = BC_ENTER_LOOPER;  binder_write(bs, readbuf, sizeof(unsigned));  for (;;) {//果然是循環    bwr.read_size = sizeof(readbuf);    bwr.read_consumed = 0;    bwr.read_buffer = (unsigned) readbuf;     res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);   //哈哈，收到請求了，解析命令    res = binder_parse(bs, 0, readbuf, bwr.read_consumed, func); } 這個...后面還要說嗎？？恩，最后有一個類似handleMessage的地方處理各種各樣的命令。這個就是svcmgr_handler,就在ServiceManager.c中int svcmgr_handler(struct binder_state *bs,          struct binder_txn *txn,          struct binder_io *msg,          struct binder_io *reply){  struct svcinfo *si;  uint16_t *s;  unsigned len;  void *ptr;   s = bio_get_string16(msg, &len);  switch(txn->code) {  case SVC_MGR_ADD_SERVICE:    s = bio_get_string16(msg, &len);    ptr = bio_get_ref(msg);    if (do_add_service(bs, s, len, ptr, txn->sender_euid))      return -1;    break;...其中，do_add_service真正添加BnMediaService信息int do_add_service(struct binder_state *bs,          uint16_t *s, unsigned len,          void *ptr, unsigned uid){  struct svcinfo *si;  si = find_svc(s, len);s是一個list   si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));    si->ptr = ptr;    si->len = len;    memcpy(si->name, s, (len + 1) * sizeof(uint16_t));    si->name[len] = '/0';    si->death.func = svcinfo_death;    si->death.ptr = si;    si->next = svclist;    svclist = si; //看見沒，這個svclist是一個列表，保存了當前注冊到ServiceManager中的信息  }  binder_acquire(bs, ptr);//這個嗎。當這個Service退出后，我希望系統通知我一下，好釋放上面malloc出來的資源。大概就是干這個事情的。  binder_link_to_death(bs, ptr, &si->death);  return 0;}

class MediaPlayerService : public BnMediaPlayerService// MediaPlayerService從BnMediaPlayerService派生//而BnMediaPlayerService從BnInterface和IMediaPlayerService同時派生class BnMediaPlayerService: public BnInterface<IMediaPlayerService>{public:  virtual status_t  onTransact( uint32_t code,                  const Parcel& data,                  Parcel* reply,                  uint32_t flags = 0);};看起來，BnInterface似乎更加和打開設備相關啊。template<typename INTERFACE>class BnInterface : public INTERFACE, public BBinder{public:  virtual sp<IInterface>   queryLocalInterface(const String16& _descriptor);  virtual const String16&   getInterfaceDescriptor() const; protected:  virtual IBinder*      onAsBinder();};兌現后變成class BnInterface : public IMediaPlayerService, public BBinderBBinder?BpBinder？是不是和BnXXX以及BpXXX對應的呢？如果是，為什么又叫BBinder呢？BBinder::BBinder()  : mExtras(NULL){//沒有打開設備的地方啊？}

int main(int argc, char** argv){//對啊，我在ProcessState中不是打開過binder了嗎？   sp<ProcessState> proc(ProcessState::self());  sp<IServiceManager> sm = defaultServiceManager();MediaPlayerService::instantiate();   ......

...//難道是下面兩個？ProcessState::self()->startThreadPool();IPCThreadState::self()->joinThreadPool();看看startThreadPool吧void ProcessState::startThreadPool(){ ...  spawnPooledThread(true);}void ProcessState::spawnPooledThread(bool isMain){  sp<Thread> t = new PoolThread(isMain);isMain是TRUE//創建線程池，然后run起來，和java的Thread何其像也。  t->run(buf); }PoolThread從Thread類中派生，那么此時會產生一個線程嗎？看看PoolThread和Thread的構造吧PoolThread::PoolThread(bool isMain)    : mIsMain(isMain)  {  }Thread::Thread(bool canCallJava)//canCallJava默認值是true  :  mCanCallJava(canCallJava),    mThread(thread_id_t(-1)),    mLock("Thread::mLock"),    mStatus(NO_ERROR),    mExitPending(false), mRunning(false){} 喔，這個時候還沒有創建線程呢。然后調用PoolThread::run，實際調用了基類的run。status_t Thread::run(const char* name, int32_t priority, size_t stack){ bool res;  if (mCanCallJava) {    res = createThreadEtc(_threadLoop,//線程函數是_threadLoop        this, name, priority, stack, &mThread);  }//終于，在run函數中，創建線程了。從此主線程執行IPCThreadState::self()->joinThreadPool();新開的線程執行_threadLoop我們先看看_threadLoopint Thread::_threadLoop(void* user){  Thread* const self = static_cast<Thread*>(user);  sp<Thread> strong(self->mHoldSelf);  wp<Thread> weak(strong);  self->mHoldSelf.clear();   do { ...    if (result && !self->mExitPending) {        result = self->threadLoop();哇塞，調用自己的threadLoop      }    }我們是PoolThread對象，所以調用PoolThread的threadLoop函數virtual bool PoolThread ::threadLoop()  {//mIsMain為true。//而且注意，這是一個新的線程，所以必然會創建一個新的IPCThreadState對象（記得線程本地存儲嗎？TLS），然后   IPCThreadState::self()->joinThreadPool(mIsMain);    return false;  }主線程和工作線程都調用了joinThreadPool，看看這個干嘛了！void IPCThreadState::joinThreadPool(bool isMain){   mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER);   status_t result;  do {    int32_t cmd;     result = talkWithDriver();     result = executeCommand(cmd);    }    } while (result != -ECONNREFUSED && result != -EBADF);   mOut.writeInt32(BC_EXIT_LOOPER);  talkWithDriver(false);}看到沒？有loop了，但是好像是有兩個線程都執行了這個啊！這里有兩個消息循環？下面看看executeCommandstatus_t IPCThreadState::executeCommand(int32_t cmd){BBinder* obj;  RefBase::weakref_type* refs;  status_t result = NO_ERROR;case BR_TRANSACTION:    {      binder_transaction_data tr;      result = mIn.read(&tr, sizeof(tr));//來了一個命令，解析成BR_TRANSACTION,然后讀取后續的信息    Parcel reply;       if (tr.target.ptr) {//這里用的是BBinder。        sp<BBinder> b((BBinder*)tr.cookie);        const status_t error = b->transact(tr.code, buffer, &reply, 0);}讓我們看看BBinder的transact函數干嘛了status_t BBinder::transact(  uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){就是調用自己的onTransact函數嘛   err = onTransact(code, data, reply, flags);  return err;}

status_t BnMediaPlayerService::onTransact(  uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){// BnMediaPlayerService從BBinder和IMediaPlayerService派生，所有IMediaPlayerService//看到下面的switch沒？所有IMediaPlayerService提供的函數都通過命令類型來區分//  switch(code) {    case CREATE_URL: {      CHECK_INTERFACE(IMediaPlayerService, data, reply);      create是一個虛函數，由MediaPlayerService來實現！！sp<IMediaPlayer> player = create(          pid, client, url, numHeaders > 0 ? &headers : NULL);       reply->writeStrongBinder(player->asBinder());      return NO_ERROR;    } break;

IMediaDeathNotifier::getMediaPlayerService(){    sp<IServiceManager> sm = defaultServiceManager();    sp<IBinder> binder;    do {//向SM查詢對應服務的信息，返回binder      binder = sm->getService(String16("media.player"));      if (binder != 0) {        break;       }       usleep(500000); // 0.5 s    } while(true); //通過interface_cast，將這個binder轉化成BpMediaPlayerService//注意，這個binder只是用來和binder設備通訊用的，實際//上和IMediaPlayerService的功能一點關系都沒有。//還記得我說的Bridge模式嗎?BpMediaPlayerService用這個binder和BnMediaPlayerService//通訊。  sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);  }  return sMediaPlayerService;}

int main(){ getMediaPlayerService();直接調用這個函數能獲得BpMediaPlayerService嗎？不能，為什么？因為我還沒打開binder驅動吶！但是你在JAVA應用程序里邊卻有google已經替你封裝好了。所以，純native層的代碼，必須也得像下面這樣處理：sp<ProcessState> proc(ProcessState::self());//這個其實不是必須的，因為//好多地方都需要這個，所以自動也會創建.getMediaPlayerService();還得起消息循環吶，否則如果Bn那邊有消息通知你，你怎么接受得到呢？ProcessState::self()->startThreadPool();//至于主線程是否也需要調用消息循環，就看個人而定了。不過一般是等著接收其他來源的消息，例如socket發來的命令，然后控制MediaPlayerService就可以了。}

int main(){ sp<ProcessState> proc(ProcessState::self());sp<IServiceManager> sm = defaultServiceManager();sm->addService(“service.name”,new XXXService());ProcessState::self()->startThreadPool();IPCThreadState::self()->joinThreadPool();}看看XXXService怎么定義呢？我們需要一個Bn，需要一個Bp，而且Bp不用暴露出來。那么就在BnXXX.cpp中一起實現好了。另外，XXXService提供自己的功能，例如getXXX調用

class IXXX: public IInterface{public:DECLARE_META_INTERFACE(XXX);申明宏virtual getXXX() = 0;virtual setXXX() = 0;}這是一個接口。

class BnXXX: public BnInterface<IXXX>{public:  virtual status_t  onTransact( uint32_t code,                  const Parcel& data,                  Parcel* reply,                  uint32_t flags = 0);//由于IXXX是個純虛類，而BnXXX只實現了onTransact函數，所以BnXXX依然是一個純虛類};

IMPLEMENT_META_INTERFACE(XXX, "android.xxx.IXXX");//IMPLEMENT宏 status_t BnXXX::onTransact(  uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){  switch(code) {    case GET_XXX: {      CHECK_INTERFACE(IXXX, data, reply);      讀請求參數      調用虛函數getXXX()      return NO_ERROR;    } break; //SET_XXX類似

class BpXXX: public BpInterface<IXXX>{public:  BpXXX (const sp<IBinder>& impl)    : BpInterface< IXXX >(impl)  {}vitural getXXX(){ Parcel data, reply; data.writeInterfaceToken(IXXX::getInterfaceDescriptor());  data.writeInt32(pid);  remote()->transact(GET_XXX, data, &reply);  return;}//setXXX類似