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
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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
1 int DemoService::instantiate() {
2 LOGE("DemoService instantiate");
3 int r = defaultServiceManager()->DemoService(
4 String16("alfred.demo"), new DemoService());
5 LOGE("DemoService r = %d\n", r);
6 return r;
7 }
8
9
10 status_t DemoService::onTransact(
11 uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){
12 switch(code) {
13 case 0: {
14 pid_t pid = data.readInt32();
15 int num = data.readInt32();
16 num = num + 1000;
17 reply->writeInt32(num);
18 return NO_ERROR;
19 } break;
20 default:
21 return BBinder::onTransact(code, data, reply, flags);
22 }
23 }
(2) 编写DemoLoader启动DemoNativeService
1 int main(int argc, char** argv)
2 {
3 sp<ProcessState> proc(ProcessState::self());
4 sp<IServiceManager> sm = defaultServiceManager();
5 LOGI("ServiceManager: %p", sm.get());
6 DemoService::instantiate();
7 ProcessState::self()->startThreadPool();
8 IPCThreadState::self()->joinThreadPool();
9 }
(3) 编写mk文件
(4) 编写Native代码调用DemoNativeService
1 int Demo::setN(int n){
2 getDemoService();
3 Parcel data, reply;
4 data.writeInt32(getpid());
5 data.writeInt32(n);
6
7 LOGE("BpDemoService::create remote()->transact()\n");
8 binder->transact(0, data, &reply);
9 int i = reply.readInt32();
10 return i;
11 }
12 const void Demo::getDemoService(){
13 sp<IServiceManager> sm = defaultServiceManager();
14 binder = sm->getService(String16("guilh.add"));
15 LOGE("Add::getDemoService %p\n",sm.get());
16 if (binder == 0) {
17 LOGW("DemoService not published, waiting...");
18 return;
19 }
20 }
(5) 使用JNI实现Java和NativeService的衔接
(6) 在Activity中调用DemoNativeService