Android Binder机制(6) 编写自己的本地服务

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引言

前面几篇博客中系统地介绍了本地服务的注册、检索以及使用过程。这篇博客我们将完成一个属于自己的本地服务:AllenService。

由前面的学习知道，要完成一个自己的本地服务，需要有IAllenService接口、BnAllenService服务Stub、AllenService、BpAllenService。UML图如下：

AllenService

各文件的路径如下：

  • frameworks/base/include/allen/IAllenService.h,AllenService.h

  • frameworks/base/libs/allen/IAllenService.cpp,AllenService.cpp

  • frameworks/base/cmds/allen/main_allenclient.cpp,main_allenservice.cpp

1.IAllenService.h文件

该头文件中包含了接口描述符以及枚举类。另外，与Android中的服务接口文件类似，这里将BnAllenService的定义也放在该头文件中，所以该头文件的代码如下： 

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#ifndef FRAMEWORKS_BASE_INCLUDE_IALLENSERVICE_H_
#define FRAMEWORKS_BASE_INCLUDE_IALLEN_SERVICE_H_
#include <utils/Errors.h>
#include <utils/KeyedVector.h>
#include <utils/RefBase.h>
#include <utils/String8.h>
#include <binder/IInterface.h>
#include <binder/Parcel.h>
#include <AllenService.h>
namespace android{
    #define MATH_ERROR int32(-1)
    #define ALLEN_DESCRIPTOR "android.allen.IAllenService"
    enum{
        ALLEN_PRINT=IBinder::FIRST_CALL_TRANSACTION,
        ALLEN_ADD,
        ALLEN_SUB
    };
    class IAllenService:public IInterface
    {
        public:
            //宏定义
            DECLARE_META_INTERFACE(AllenService);
            virtual status_t print(const char*str)=0;
            virtual int32 add(int32 a,int32 b)=0;
            virtual int32 sub(int32 a,int32 b)=0;
    };
    class BnAllenService:public BnInterface<IAllenService>
    {
        public:
            virtual status_t onTransact(uint32_t code,
                                        const Parcel& data,
                                        Parcel*reply,
                                        uint32_t flags=0);
    };
};//namespace android
#endif

2. AllenService.h

AllenService头文件的代码如下： 

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#ifndef FRAMEWORKS_BASE_INCLUDE_ALLEN_ALLENSERVICE_H_
#define FRAMEWORKS_BASE_INCLUDE_ALLEN_ALLENSERVICE_H_
#include <utils/Log.h>
#include <utils/threads.h>
#include <utils/List.h>
#include <utils/Errors.h>
#include <utils/KeyedVector.h>
#include <utils/String8.h>
#include <utils/Vector.h>
#include <IAllenService.h>
namespace android{
    class AllenService:public BnAllenService{
        public:
            static void instantiate();
            virtual status_t print(const char*str);
            virtual int32 add(int32 a,int32 b);
            virtual int32 sub(int32 a,int32 b);
            virtual status_t onTransact(
                    uint32_t code,
                    const Parcel& data,
                    Parcel* reply,
                    uint32_t flags);
        private:
            AllenService();
            virtual ~AllenService();
    };
}; //namespace android
#endif

3. IAllenService.cpp

该文件中不仅有IAllenService中宏接口的实现，还有BnAllenService的实现，另外，还有BpAllenService的定义以及实现。 

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#include <stdint.h>
#include <sys/types.h>
#include <binder/Parcel.h>
#include <binder/IMemory.h>
#include <allen/IAllenService.h>
#include <allen/AllenService.h>
#include <utils/Errors.h>
namespace android{
    class BpAllenService: public BpInterface<IAllenService>
    {
        public:
            BpAllenService(const sp<IBinder>& impl):BpInterface<IAllenService>(impl)
            {
            }
            virtual status_t print(const char*str)
            {
                Parcel data,reply;
                data.writeInterfaceToken(IAllenService::getInterfaceDescriptor());
                data.writeCString(str);
                status_t status=remote()->transact(ALLEN_PRINT,data,&reply);
                if(status!=NO_ERROR){
                    LOGE("print str error:%s",strerror(-status));
                }else{
                    status=reply.readInt32();
                }
                return status;
            }
            virtual int32 add(int32 a,int32 b)
            {
                Parcel data,reply;
                data.writeInterfaceToken(IAllenService::getInterfaceDescriptor());
                data.writeInt32(a);
                data.writeInt32(b);
                status_t status=remote()->transact(ALLEN_ADD,data,&reply);
                return reply.readInt32();
            }
            virtual int32 sub(int32 a,int32 b)
            {
                Parcel data,reply;
                data.writeInterfaceToken(IAllenService::getInterfaceDescriptor());
                data.writeInt32(a);
                data.writeInt32(b);
                status_t status=remote()->transact(ALLEN_SUB,data,&reply);
                return reply.readInt32();
            }
    };
    //宏实现
    IMPLEMENT_META_INTERFACE(AllenService,ALLEN_DESCRIPTOR)
    status BnAllenService::onTransact(uint32_t code,const Parcel& data,Parcel* reply,uint32_t flags)
    {
        switch(code){
            case ALLEN_PRINT:{
                CHECK_INTERFACE(IAllenService,data,reply);
                const char*str=data.readCString();
                reply->writeInt32(print(str));
                return NO_ERROR;
            }break;
            case ALLEN_ADD:{
                CHECK_INTERFAC(IAllenService,data,reply);
                int32 a=data.readInt32();
                int32 b=data.readInt32();
                reply->writeInt32(this->add(a,b));
                return NO_ERROR;
            }break;
            case ALLEN_SUB:{
                CHECK_INTERFACE(IAllenService,data,reply);
                int32 a=data.readInt32();
                int32 b=data.readInt32();
                reply->writeInt32(this->sub(a,b));
                return NO_ERROR;
            }break;
            default:
                return BBinder::onTransact(code,data,reply,flags);
        }
    }
};

4.AllenService.cpp

该文件实现服务接口。代码如下： 

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namespace android{
    void AllenService::instantiate(){
        defaultServiceManager()->addService(
            String16(ALLEN_DESCRIPTOR),new AllenService());
    }
    status_t AllenService::print(const char*str){
        LOGI("%s\n",str);
        printf("%s\n",str);
        return NO_ERROR;
    }
    int32 AllenService::add(int32 a,int32 b){
        LOGI("a=%d,b=%d",a,b);
        return a+b;
    }
    int32 AllenService::sub(int32 a,int32 b){
        LOGI("a=%d,b=%d",a,b);
        return a-b;
    }
};

5.main_allenservice.cpp

创建好AllenService后，如果想要运行它，就需要有服务客户端和Service Server进程，服务代理运行在服务客户端中，服务运行在Service Server进程中。如下图所示：

client_vs_service

main_allenservice.cpp的代码如下： 

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int main(int argc,char** argv)
{
    sp<ProcessState>proc(ProcessState::self());
    sp<IServiceManager>sm=defaultServiceManager();
    LOGI("ServiceManager: %p",sm.get());
    AllenService::instantiate();
    ProcessState::self()->startThreadPool();
    ProcessState::self()->joinThreadPool();
    return 0;
}

6.main_allenclient.cpp

main_allenclient.cpp的代码如下： 

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int main(int argc,char *argv[])
{
    LOGI("allenservice cleint is now starting");
    sp<IServiceManager>sm=defaultServiceManager();
    sp<IBinder>binder;
    sp<IAllenService>allenService;
    do{
        binder=sm->getService(String16(ALLEN_DESCRIPTOR));
        if(binder!=0)
        {
            break;
        }
        LOGI("AllenService is not working,try again...");
        usleep(500000);
    }while(true);
    allenService=interface_cast<IAllenService>(binder);
    allenService->print("Hello world!\nI'm Allen and I'm coning.\n");
    allenService->add(3,6);
    allenService->sub(1,1);
    return 0;
}

7.编译AllenService系统服务

若想编译AllenService服务代码，需要将AllenService的源码包含进Android平台源码中，再进行整体编译。首先保证头文件在/frameworks/base/include/allen下，源代码文件在/frameworks/base/libs/allen下，而后编写Android.mk文件，编写完成后，将其放到源代码目录中，以便将源代码与Android平台代码一起编译。
Android.mk文件内容如下： 

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LOCAL_PATH:=$(call my-dir)
include &(CLEAR_VARS)
LOCAL_SRC_FILES:= \
    IAllenService.cpp \
    AllenService.cpp
LOCAL_SHARED_LIBRARES :=\
    libcutils \
    libutils \
    libbinder \
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE :=liballen
include $(BUILD_SHARED_LIBRARY)

接着，编写运行main_allenservice.cpp和main_allenclient.cpp的Android.mk文件，内容如下： 

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LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
    main_allenserver.cpp
LOCAL_SHARED_LIBRARIES := \
    libutils \
    libbinder \
    liballen
    base := $(LOCAL_APTH)/../..
LOCAL_MODULE:= allenservice
incldue $(BUILD_EXECUTABLE)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
    main_allenclient.cpp
LOCAL_SHARED_LIBRARIES := \
    libutils \
    libbinder \
    liballen
base :=$(LOCAL_PATH)/../..
    LOCAL_MODULE:=allenclient
include $(BUILD_EXECUTABLE)