从零开始怎么写android native service?

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从零开始怎么写android native service?

edsam 2016-02-19 21:05:20 浏览651
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从零开始怎么写android native service

        Android service对于从事android开发的人都不是一个陌生的东西,很多人可能会觉得服务很简单。服务是简单,因为复杂的别人做了,所以才会觉得简单。我们先梳理一下服务的分类,首先有本地服务跟系统服务的区分,而在APP里写的服务大多就成为Java服务或者应用服务。

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      做APP的人写个应用服务相对来说是最简单的,因为extends了一个service后几个简单的接口就可以跑起来了,写完这种服务可能也只是对服务一知半解,因为值钱的service类Google的人已经帮你写好了,这是你的福气为你带来了便利,当然也可能会麻痹你:),但是做APP的人会有能解决问题是首要任务了,有时间还是对它了解更清楚点比较好,在此不再讨论这个。

做设备做系统的人,经常可能会去写系统服务,也就是framework下面的服务,systemserver里面注册的服务,写这种服务一般来说比较少,只有做设备系统的才会这样干,才有机会有完成的系统代码,可以在里面自由遨游,笔者三年前写过一个,可以看看【自己动手从零开始写一个完整的android Servicehttp://blog.csdn.net/edsam49/article/details/8163639

       那剩下的一个是本地服务,也就是native service,这种服务我们了解的系统里面多媒体、audio system都是写成了本地服务,这样写的好处就是运行的效率更高一点,因为C/C++先天性就比JAVA的运行效率要高一点。笔者就是由于长期主要从事的都是底层开发的,我们有时有这么一种需求,又要运行效率高,又要好移植,主要是考虑推广写东西给广大客户,那么我就写一个本地服务,这样是最独立的了,效率也最高了,那一个本地服务到底怎么写呢?大多数的人写过的服务以java服务居多,真正写本地服务的不多,本地服务相对来说又是更复杂一点的。因此决定从零开始自己动手写一个本地service,下面就大概描述一下过程。

       本地服务有四大块,服务接口(IService),服务代理(也就是BpService),服务stub(也就是BnService),服务实体(Service);下面笔者的实例就以demoNativeService来开启,力求简单,里面就写了两个接口;

首先定义好服务接口IdemoNativeService,IdemoNativeService服务接口的父类是IInterface,在里面主要是要声明一下接口,在DECLARE_META_INTERFACE(demoNativeService),代码如下:

class IdemoNativeService : public IInterface
{
public:
	enum {
		CONNECT = IBinder::FIRST_CALL_TRANSACTION,
		PRINTSTRING_CMD,
	};

public:
	DECLARE_META_INTERFACE(demoNativeService);
	virtual status_t connect(int pid,int previewhw,int intf,int fmt,int chan) = 0;
  virtual  status_t  printString(const char *str) = 0;

};

      当然定义好了IdemoNativeService的头文件,就需要去实操了,先来搞定BpdemoNativeService,它的父类是BpInterface<IdemoNativeService>,这里面主要是涉及数据的跨进程用到的parcel,读啊,写啊,按套路来,也不难,也有AIDL工具可以使用,帮你转出来,再稍微修改一下就可以了,里面有一个很重要的remote,这个和remote就是幕后功臣啊,它保存了服务实例的对象啊,它是来之BpRefBase的一个成员,生成服务的时候,会得到赋值,定义完了以后,很重要的一个程序就是要IMPLEMENT_META_INTERFACE(demoNativeService,"android.hardware.IdemoNativeService");这个宏是非常重要的,跟前面那个DECLARE是对应的,前面声明,后面实现,当然我们带的参数跟的名字是必须一致的,这样才能正常沟通嘛!

class BpdemoNativeService: public BpInterface<IdemoNativeService>
{
public:
	BpdemoNativeService(const sp<IBinder>& impl)
	: BpInterface<IdemoNativeService>(impl)
	{
	}

	virtual status_t connect(int pid,int previewhw,int intf,int fmt,int chan)
	{
		Parcel data, reply;
		data.writeInterfaceToken(IdemoNativeService::getInterfaceDescriptor());
		data.writeInt32(pid);
		data.writeInt32(previewhw);
		data.writeInt32(intf);
		data.writeInt32(fmt);
		data.writeInt32(chan);
		remote()->transact(IdemoNativeService::CONNECT, data, &reply);
		return reply.readInt32();
	}

  virtual  status_t  printString(const char *str)
  {
    Parcel data, reply;
    data.writeInterfaceToken(IdemoNativeService::getInterfaceDescriptor());
    data.writeCString(str);
    remote()->transact(IdemoNativeService::PRINTSTRING_CMD, data, &reply);
		return reply.readInt32();
  }
};

IMPLEMENT_META_INTERFACE(demoNativeService, "android.hardware.IdemoNativeService");//android.hardware.IdemoNativeService ds.demonativeservice

       接着需要写服务stub了,BndemoNativeService的父类是BnInterface<IdemoNativeService>,有没有发现BndemoNativeService跟BpdemoNativeService,都会基于接口类IdemoNativeService,这样沟通起来的接口就唯一了,就具备了对话的可能;

class BndemoNativeService: public BnInterface<IdemoNativeService>
{
public:
	virtual status_t onTransact( uint32_t code,const Parcel& data,Parcel* reply,uint32_t flags = 0);
};
status_t BndemoNativeService::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
	switch(code)
	{
		/*case CONNECT: {
			CHECK_INTERFACE(IdemoNativeService, data, reply);
			int pid         = data.readInt32();
			int previewhw   = data.readInt32();
			int intf        = data.readInt32();
			int fmt         = data.readInt32();
			int chan        = data.readInt32();
			reply->writeInt32(connect(pid,previewhw,intf,fmt,chan));
			return NO_ERROR;
			}break;
		case PRINTSTRING_CMD: {
			CHECK_INTERFACE(IdemoNativeService, data, reply);
			const char *str;
      str = data.readCString();
			reply->writeInt32(printString(str));
			return NO_ERROR;
			}break;*/

		default:
			return BBinder::onTransact(code, data, reply, flags);
	}
}

      到这就轮到了大块头service实体demoNativeService了,demoNativeService是基于BndemoNativeService,在demoNativeService里面定义了一个instantiate()接口用于添加service到servicemanager里面去,注意demoNativeService()跟析构函数~demoNativeService()需要写成private的,免得别人可以new出对象来。在里面重写了onTransact,一旦BpdemoNativeService有风吹草动,就会联动到BndemoNativeService,因为服务实体重写了onTransact,所以实际就会先执行到demoNativeService::onTransact这里来,在这里面处理不了,可以再转给BpdemoNativeService的onTransact或者直接到BBinder的onTransact;

void demoNativeService::instantiate() {
	android::defaultServiceManager()->addService(
                IdemoNativeService::descriptor, new demoNativeService());
}

demoNativeService::demoNativeService()
{
    ALOGE("demoNativeService created");
    mOpened = 1;
}

demoNativeService::~demoNativeService()
{
    ALOGE("demoNativeService destroyed");
}

 status_t  demoNativeService::connect(int pid,int previewhw,int intf,int fmt,int chan){
 	
    ALOGD("demoNativeService connect:%d, %d, %d, %d, %d", pid, previewhw, intf, fmt, chan);
   	return 88;
 	
}

 status_t  demoNativeService::printString(const char *str){
 	  ALOGD("demoNativeService printString:%s", str);
   	return 66; 
}
     
#if 1       
 status_t demoNativeService::onTransact(uint32_t code,
                                                const android::Parcel &data,
                                                android::Parcel *reply,
                                                uint32_t flags)
{
        ALOGD("OnTransact(%u,%u)", code, flags);
        
        switch(code) {
 		case CONNECT: {
			CHECK_INTERFACE(IdemoNativeService, data, reply);
			int pid         = data.readInt32();
			int previewhw   = data.readInt32();
			int intf        = data.readInt32();
			int fmt         = data.readInt32();
			int chan        = data.readInt32();
			
      ALOGD("CONNECT: %d, %d, %d, %d, %d\n", pid,previewhw,intf,fmt,chan);
			reply->writeInt32(connect(pid,previewhw,intf,fmt,chan));
			return NO_ERROR;
			}break;
			       	        	
        case PRINTSTRING_CMD: {
                CHECK_INTERFACE(IdemoNativeService, data, reply);
                const char *str;
                str = data.readCString();
                ALOGD("PrintString: %s\n", str);
                ALOGD("printString: %s\n", str);
								reply->writeInt32(printString(str));
                return NO_ERROR;
        } break;
        default:
                return BndemoNativeService::onTransact(code, data, reply, flags);
        }

        return NO_ERROR;
}
#endif

      写完了服务,那我们就再写一个可执行文件来生成一下,里面startThreadPool生成线程池,然后再调用joinThreadPool来监听变化;

    sp<ProcessState> proc(ProcessState::self());
    sp<IServiceManager> sm = defaultServiceManager();
//    ALOGI("ServiceManager: %p", sm.get());
    demoNativeService::instantiate();
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();

      写到这,可以说服务已经可以跑起来了,那我们怎么验证呢,最快的办法还是写一个可执行文件去测一下它的接口,看通没通就知道了;

       	int ret= -1;
      	int pid = IPCThreadState::self()->getCallingPid();

	      ALOGI("demoNativeService client is now starting, pid=%d", pid);

        android::sp<android::IServiceManager> sm = android::defaultServiceManager();
        android::sp<android::IBinder> binder;
        android::sp<IdemoNativeService> shw;

        do {
                binder = sm->getService(android::String16("ds.demonativeservice"));
                if (binder != 0)
                        break;
                ALOGW("IdemoNativeService not published, waiting...");
                usleep(500000);
        } while(true); 

	     ALOGI("IdemoNativeService client is now trying");

       shw = android::interface_cast<IdemoNativeService>(binder);
       ret = shw->printString("Good man desheng");
	     ALOGI("demoNativeService client printString, ret=%d", ret);
       
       ret = shw->connect(pid,1, 2, 3, 4);
	     ALOGI("demoNativeService client connect, ret=%d", ret);

    下面就是笔者测试的打印,如下:

# dem
demoNativeServiceclient   demoNativeServiceserver   
# demoNativeServiceserver &                                                    
[2] 2332
# --------- beginning of /dev/log/main
02-19 17:10:57.890 E/HelloWorldService( 2332): demoNativeService created

# 
# dem
demoNativeServiceclient   demoNativeServiceserver   
# demoNativeServiceclient                                                      
02-19 17:11:02.520 I/demoNativeService/Service( 2334): demoNativeService client is now starting, pid=2334
02-19 17:11:02.520 I/demoNativeService/Service( 2334): IdemoNativeService client is now trying
02-19 17:11:02.520 D/HelloWorldService( 2332): OnTransact(2,16)
02-19 17:11:02.520 D/HelloWorldService( 2332): PrintString: Good man desheng
02-19 17:11:02.520 D/HelloWorldService( 2332): printString: Good man desheng
02-19 17:11:02.520 D/HelloWorldService( 2332): demoNativeService printString:Good man desheng
02-19 17:11:02.520 I/demoNativeService/Service( 2334): demoNativeService client printString, ret=66
02-19 17:11:02.520 D/HelloWorldService( 2332): OnTransact(1,16)
02-19 17:11:02.520 D/HelloWorldService( 2332): CONNECT: 2334, 1, 2, 3, 4
02-19 17:11:02.520 D/HelloWorldService( 2332): demoNativeService connect:2334, 1, 2, 3, 4
02-19 17:11:02.520 I/demoNativeService/Service( 2334): demoNativeService client connect, ret=88
02-19 17:11:02.520 I/demoNativeService/Service( 2334): Hello client is now exiting
# 
# 02-19 17:11:07.540 D/InitAlarmsService( 2259): Clearing and rescheduling alarms.

# service list
Found 78 services:
0	ds.demonativeservice: [android.hardware.IdemoNativeService]
1	phone: [com.android.internal.telephony.ITelephony]
2	iphonesubinfo: [com.android.internal.telephony.IPhoneSubInfo]
3	simphonebook: [com.android.internal.telephony.IIccPhoneBook]
4	isms: [com.android.internal.telephony.ISms]
5	jeavoxmiddleware: [android.jeavox.IMiddleWareService]

    写到这,如果要给应用调用的话,还需要写Client,JNI,JNI及以上在此不再讨论了,我们就简易来看看client怎么处理吧,其实有点类似上面那个可执行文件的写法,这里可能就是有一个对象的概念,可以保持,大概如下:

demoNativeServiceClient::demoNativeServiceClient()
{
	sp<IServiceManager> sm = defaultServiceManager();
	sp<IBinder> binder = sm->getService(String16("ds.demonativeservice"));
	mdemoNativeService = interface_cast<IdemoNativeService>(binder);
}

demoNativeServiceClient::~demoNativeServiceClient()
{
	mdemoNativeService = NULL;
}

int32_t demoNativeServiceClient::connect(int previewhw,int intf,int fmt,int chan)
{
	return mdemoNativeService->connect(getCallingPid(),previewhw,intf,fmt,chan);
}

int32_t demoNativeServiceClient::printString(const char *str)
{
   return mdemoNativeService->printString(str);
}

     罗哩罗嗦写了这么多,请大家拍砖,轻拍一下:)

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