Android系统中通过binder(AIDL)进行跨层IPC通信

       Binder是Android系统进程间通信（IPC）常用方式之一，client/service端是通过binder驱动作为通信介质的。Android系统中可以通过binder，实现JAVA/C++层的双向IPC通信，即JAVA - JAVA 、 JAVA - C++ 、 C++ - C++ 都可以通过Binder进行IPC双向通信。

      在Android 系统中个，很多模块的service放到了native层，用C++去实现，例如CameraService、SurfaceFlinger等。Client端则可以通过ServiceManger去获取service对象，然后通过AIDL接口进行服务端的调用。至于为什么没有用到JNI，是因为Android系统以及都帮忙做好了，在此只谈应用。

     下面举个例子，介绍 客户端(JAVA) 和 服务端(C++）通过 binder(AIDL)实现IPC双向通信用例。

1、创建AIDL文件，可以放在一个公共目录中，以方便client/service端都可以通过mk文件将其编译进去。

      再test目录下面 新建aidl目录 aidl\com\test\evs\ ，然后新建两个aidl文件 IEvsTestInterface.aidl (调用) IEvsTestCallback.aidl (回调)

 IEvsTestCallback.aidl

package com.test.evs;

interface IEvsTestCallback {

    void onEvsStatus(int type, int arg0, int arg1);

    void onErrorStatus(int type, int value);
}

IEvsTestInterface.aidl

package com.test.evs;

import com.test.evs.IEvsTestCallback;

interface IEvsTestInterface {

    void setCmd(int type, int arg0);

    int getStatus(int type, int arg0);

    void registerEvsCallback(IEvsTestCallback callback);
}

 

2、JAVA client端实现

为方便测试，JAVA client端则直接编译成一个apk进行测试。

Test 目录下面创建一个 test_client目录，存放client端的code

MainActivity.java

package com.example.sampletest;

import android.content.Context;
import android.os.Bundle;
import android.os.IBinder;
import android.os.Parcel;
import android.os.RemoteException;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.os.ServiceManager;
import android.app.Activity;

import com.test.evs.IEvsTestInterface;
import com.test.evs.IEvsTestCallback;

public class MainActivity extends Activity {
	
    private static final String TAG = "sampleService";
    private static final java.lang.String DESCRIPTOR = "evs.test";
    private static final int FUNC_CALLFUNCTION = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
    } 
    
    private void initData() {
    	Log.i(TAG, "client initData");
    	
    	//Parcel _data = Parcel.obtain();
    	//Parcel _reply = Parcel.obtain();
    	
    	IBinder binder = ServiceManager.getService(DESCRIPTOR); //服务端对象
        if (binder == null) {
            Log.d(TAG, "biner get is null");
        }

        IEvsTestInterface evsInterface = IEvsTestInterface.Stub.asInterface(binder);
        
        if (evsInterface != null) {
            try {
                evsInterface.registerEvsCallback(callback); // 注册回调
                evsInterface.setCmd(1, 100);
                Log.d(TAG, "setCmd");
            } catch (RemoteException e) {

            }
        }
        
    	Log.i(TAG, "client initData end");
    	
    }

    private IEvsTestCallback callback = new IEvsTestCallback.Stub() {
        @Override
        public void onEvsStatus(int type, int arg0, int arg1)
              throws RemoteException {
           Log.i(TAG, "onEvsStatus " + type + " " + arg0 + " " + arg1);
        }
        
        @Override
        public void onErrorStatus(int type, int value) 
             throws RemoteException {
       
        }
    };
}

Client 端 mk文件

Android.mk，需要将aidl 文件编译进去，以便生成 .java文件。

Android.mk

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

LOCAL_STATIC_JAVA_LIBRARIES := android-support-v13
LOCAL_STATIC_JAVA_LIBRARIES += android-ex-camera2-portability
LOCAL_STATIC_JAVA_LIBRARIES += xmp_toolkit
LOCAL_STATIC_JAVA_LIBRARIES += glide
LOCAL_STATIC_JAVA_LIBRARIES += guava
LOCAL_STATIC_JAVA_LIBRARIES += jsr305

LOCAL_AIDL_INCLUDES := $(LOCAL_PATH)/../aidl

LOCAL_SRC_FILES := $(call all-java-files-under, src) \
   ../aidl/com/test/evs/IEvsTestCallback.aidl \
   ../aidl/com/test/evs/IEvsTestInterface.aidl \
  
#LOCAL_SRC_FILES += $(call all-java-files-under, src_pd)
#LOCAL_SRC_FILES += $(call all-java-files-under, src_pd_gcam)

LOCAL_RESOURCE_DIR += \
	$(LOCAL_PATH)/res \

LOCAL_PACKAGE_NAME := evsClient

LOCAL_CERTIFICATE := platform

3、native C++ 端

在test目录下面创建 test_server目录，并新建

EvsTestService.h EvsTestService.cpp main.cpp 三个文件

EvsTestService.h，会继承 BnEvsTestInterface 类，它是由AIDL文件在服务端编译生成的。

#ifndef _EVS_TEST_SERVICE_H
#define _EVS_TEST_SERVICE_H

#include 
#include 

#include 
#include 
#include 
#include 
#include 
#include 

using namespace android;
//using namespace android::notification;
using namespace android::binder;
using namespace std;

namespace android {
class EvsTestService :
     public com::test::evs::BnEvsTestInterface,
     public IBinder::DeathRecipient
{
public:
    EvsTestService();
    virtual ~EvsTestService();
    virtual binder::Status setCmd(int type, int arg0) override;
    virtual binder::Status getStatus(int type, int arg0, int32_t* _aidl_return) override;
    virtual binder::Status registerEvsCallback(const ::android::sp<::com::test::evs::IEvsTestCallback>& callback) override;

    void sendMsgToClient(int status, int arg0, int arg1);
private:
    void binderDied(const wp& who) override;

    android::sp<::com::test::evs::IEvsTestCallback> callback_;
    std::mutex mutex_;
    
};
}

#endif 

EvsTestService.cpp 文件

#include 
#include 
#include 

#include "EvsTestService.h"

namespace android {

    EvsTestService::EvsTestService() {
        ALOGI("EvsTestService...");
    }

    EvsTestService::~EvsTestService() {

    }

    binder::Status EvsTestService:: setCmd(int type, int arg0) {
	ALOGI("setCmd %d, %d\n", type, arg0);
        //status_t res;

        sendMsgToClient(type, arg0, 101);
        return binder::Status::ok();
    }

    binder::Status EvsTestService::getStatus(int type, int arg0, int32_t* _aidl_return) {
       ALOGI("getStatus %d, %d", type, arg0);
       *_aidl_return = 1;
       return binder::Status::ok();
    }

    binder::Status EvsTestService::registerEvsCallback(const ::android::sp<::com::test::evs::IEvsTestCallback>& callback) {
        //mcallback = callback;
        //callback = nullptr;
        
        std::lock_guard < std::mutex > guard(mutex_);
        if (callback_.get()) {
            ALOGD("Notification>>Failed to register callback, already registered");
            return binder::Status::fromStatusT(ALREADY_EXISTS);
        }
        ALOGD("Notification>>Success to register callback, already registered");
        callback_ = callback;
        IInterface::asBinder(callback_)->linkToDeath(this);

        return binder::Status::ok();
    }

    void EvsTestService:: sendMsgToClient(int type, int arg0, int arg1) {
        if (!callback_.get()) {
            ALOGD("Notification>>INotificationGatewayCallback callback_ is null");
            return;
        }
        ALOGD("SendMsgToClient %d, %d, %d", type, arg0, arg1);
        binder::Status status = callback_->onEvsStatus(type, arg0, arg1);
    }

    void EvsTestService::binderDied(const wp& /* who */) {
        std::lock_guard < std::mutex > guard(mutex_);
        callback_ = nullptr;
    }
}

Main.cpp

#include "EvsTestService.h"
#include 

#include 
#include 
#include 
#include 
#include 
#include 

int main() {
     sp  server = new EvsTestService();

     sp  sm = defaultServiceManager();
     EvsTestService* samServ = new EvsTestService();
     status_t ret = sm->addService(String16("evs.test"), samServ); //注册服务 
     ALOGI("Service main addservice %d ", ret);
     ProcessState::self()->startThreadPool();
     IPCThreadState::self()->joinThreadPool(true);
    // while(1);
     return 0;
}

Android.mk, 将服务端编译成可执行文件，也需要将aidl文件编译进去。

LOCAL_PATH:= $(call my-dir)

##################################
include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

LOCAL_STATIC_JAVA_LIBRARIES := android-support-v13
LOCAL_STATIC_JAVA_LIBRARIES += android-ex-camera2-portability
LOCAL_STATIC_JAVA_LIBRARIES += xmp_toolkit
LOCAL_STATIC_JAVA_LIBRARIES += glide
LOCAL_STATIC_JAVA_LIBRARIES += guava
LOCAL_STATIC_JAVA_LIBRARIES += jsr305

#LOCAL_AIDL_INCLUDES := $(LOCAL_PATH)/ 
LOCAL_AIDL_INCLUDES := $(LOCAL_PATH)/../aidl \

LOCAL_SRC_FILES := \
   EvsTestService.cpp \
    main.cpp \
    ../aidl/com/test/evs/IEvsTestCallback.aidl \
    ../aidl/com/test/evs/IEvsTestInterface.aidl \

LOCAL_SHARED_LIBRARIES := \
    libui \
    libgui \
    libEGL \
    libGLESv2 \
    libbase \
    libbinder \
    libcutils \
    libhardware \
    libhidlbase \
    libhidltransport \
    liblog \
    libutils \

#LOCAL_EXPORT_SHARED_LIBRARY_HEADERS := libbinder libcamera_client libfmq

LOCAL_C_INCLUDES += \
    system/media/private/camera/include \
    frameworks/native/include/media/openmax

#LOCAL_EXPORT_C_INCLUDE_DIRS := \
#    frameworks/av/services/camera/libcameraservice

LOCAL_MODULE := evsServer

#LOCAL_MODULE_TAGS := optional
#LOCAL_STRIP_MODULE := keep_symbols

LOCAL_CFLAGS += -DLOG_TAG=\"EvsSample\"
#LOCAL_CFLAGS += -DGL_GLEXT_PROTOTYPES -DEGL_EGLEXT_PROTOTYPES
LOCAL_CFLAGS +=  

# NOTE:  It can be helpful, while debugging, to disable optimizations
#LOCAL_CFLAGS += -O0 -g

include $(BUILD_EXECUTABLE)
#include $(BUILD_SHARED_LIBRARY)

4、测试

  先将服务器进程运行起来，然后在将client的apk 跑起来，查看log。