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在checkService的调查中我们知道客户端向ServiceManager请求服务名，ServiceManager根据服务名遍历本地链表，找到匹配的handle返回给客户端。这个handle显然是由服务端注册的，这个handle究竟是什么？要先搞清楚这个问题，必须研究服务端和ServiceManager是如何共同完成一次addService操作的。我们从服务端代码出发。TestService.cpp:30
int main() { sp < ProcessState > proc(ProcessState::self()); sp < IServiceManager > sm = defaultServiceManager(); // sm = new BpServiceManager(new BpBinder(0)) sm->addService(String16("service.testservice"), new BnTestService()); ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool(); return 0; }
在《defaultServiceManager()返回了什么？》一文中已经知道，sm就是new BpServiceManager(new BpBinder( 0 ) )，因此，找到BpServiceManager::addService(…)，frameworks/native/libs/binder/IServiceManager.cpp:155
virtual status_t addService(const String16& name, const sp<IBinder>& service, bool allowIsolated) { // name="service.testservice", service=new BnTestService()，allowIsolated=false Parcel data, reply; data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor()); data.writeString16(name); data.writeStrongBinder(service); data.writeInt32(allowIsolated ? 1 : 0); status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply); return err == NO_ERROR ? reply.readExceptionCode() : err; }
Parcel的数据组织规则参见《Parcel是怎么打包的？》。这里打包的service是由main函数传入的new BnTestService()，它的类型是remote还是local呢？从命名上来看我猜是local（BpXXX代表proxy，BnXXX代表native）。来看看BnTestService的继承关系：BnTestService继承自BnInterface<ITestService>，BnInterface继承自BBinder，BBinder覆盖了虚函数localBinder(){return this;}在Binder.cpp:191。因此这个Parcel data的示意图为：
binder->localBinder()返回binder的this指针，因此就是传入的service参数，即new BnTestService()。
接下来在BpServiceManager::addService(…)函数中调用remote()->transact(…)组织数据的过程在《binder客户端是如何组织checkService数据》中已经分析过了，不再详细解释，只列出关键节点：
frameworks/native/libs/binder/IServiceManager.cpp:155
virtual status_t addService(const String16& name, const sp<IBinder>& service, bool allowIsolated) { // name="service.testservice", service=new BnTestService()，allowIsolated=false Parcel data, reply; …… status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply); …… }
frameworks/native/libs/binder/BpBinder.cpp:159
status_t BpBinder::transact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { // code=ADD_SERVICE_TRANSACTION, flags=0 // Once a binder has died, it will never come back to life. …… status_t status = IPCThreadState::self()->transact( mHandle, code, data, reply, flags); …… }
frameworks/native/libs/binder/IPCThreadState.cpp:548
status_t IPCThreadState::transact(int32_t handle, uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { // handle=0, code=ADD_SERVICE_TRANSACTION, flags=0 status_t err = data.errorCheck(); flags |= TF_ACCEPT_FDS; …… err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL); …… return err; }
frameworks/native/libs/binder/IPCThreadState.cpp:904
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags, int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer) { // cmd=BC_TRANSACTION, binderFlags=TF_ACCEPT_FDS, handle=0, // code=ADD_SERVICE_TRANSACTION, binder_transaction_data tr; tr.target.ptr = 0; /* Don‘t pass uninitialized stack data to a remote process */ tr.target.handle = handle; tr.code = code; tr.flags = binderFlags; tr.cookie = 0; tr.sender_pid = 0; tr.sender_euid = 0; …… tr.data_size = data.ipcDataSize(); tr.data.ptr.buffer = data.ipcData(); tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t); tr.data.ptr.offsets = data.ipcObjects(); …… mOut.writeInt32(cmd); mOut.write(&tr, sizeof(tr)); return NO_ERROR; }
它组织成最终的请求数据为：
Binder学习笔记（六）—— binder服务端是如何组织addService数据的
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原文地址：http://www.cnblogs.com/palance/p/5472298.html
