一、Service的分类
1.1>Android Service
使用Java编写在JVM中运行的服务
1.2>Native Service
使用C/C++完成的服务，一般在系统开始时完成初始化，如MediaService, Audio Service等。
二、Native Service工作流程分析
int main(int argc, char** argv) { sp<ProcessState> proc(ProcessState::self()); sp<IServiceManager> sm = defaultServiceManager(); LOGI("ServiceManager: %p", sm.get()); AudioFlinger::instantiate(); MediaPlayerService::instantiate(); CameraService::instantiate(); AudioPolicyService::instantiate(); ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool(); } |
2.1、创建ProcessState和DefaultServiceManager
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ProcessState放置在全局变量gProcess中，每个进程只有一个ProcessState对象，负责打开Binder设备驱动，建立线程池等。而IPCThreadState每个线程有一个，IPCThreadState实例登记在Linux线程程的上下文附属数据中，主要负责Binder数据读取，写入和请求处理框架。IPCThreadSate在构造的时候，获取进程的ProcessSate并记录在自己的成员变量mProcess中,通过mProcess可以获取到Binder的句柄。
2.2、将服务放进ServiceManager
AudioFlinger::instantiate();
===>>
defaultServiceManager()->addService(String16("media.audio_flinger"), new AudioFlinger());
2.3、开始服务循环
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
a读取/写入：talkWithDriver（）@IPCThreadState对ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr)进行包装。
b请求处理：executeCommand(...)@ IPCThreadState
c循环结构：joinThreadPool()
joinThreadPool(){
While(1){
talkWithDriver(...)
...
executeCommand(...)
}
}
2.4、透过 IBinder::transact() 函数来与核心服务互传数据。
三、编写自己的Native Service
(1) 编写DemoNativeService
int DemoService::instantiate() {
LOGE("DemoService instantiate");
int r = defaultServiceManager()->DemoService(
String16("alfred.demo"), new DemoService());
LOGE("DemoService r = %d\n", r);
return r;
}
status_t DemoService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){
switch(code) {
case 0: {
pid_t pid = data.readInt32();
int num = data.readInt32();
num = num + 1000;
reply->writeInt32(num);
return NO_ERROR;
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
} (2) 编写DemoLoader启动DemoNativeService
int main(int argc, char** argv)
{
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
LOGI("ServiceManager: %p", sm.get());
DemoService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
(3) 编写mk文件
(4) 编写Native代码调用DemoNativeService
int Demo::setN(int n){
getDemoService();
Parcel data, reply;
data.writeInt32(getpid());
data.writeInt32(n);
LOGE("BpDemoService::create remote()->transact()\n");
binder->transact(0, data, &reply);
int i = reply.readInt32();
return i;
}
const void Demo::getDemoService(){
sp<IServiceManager> sm = defaultServiceManager();
binder = sm->getService(String16("guilh.add"));
LOGE("Add::getDemoService %p\n",sm.get());
if (binder == 0) {
LOGW("DemoService not published, waiting...");
return;
}
}(5) 使用JNI实现Java和NativeService的衔接
(6) 在Activity中调用DemoNativeService