Android Framework增加新的系统服务详解

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Android Framework系统服务详解

Android Framework系统服务详解

操作环境

系统：Linux (Ubuntu 12.04)

平台：高通

Android版本：5.1

PS: 符号…为省略N条代码

一、大致原理分析

Android本身有很多系统服务，如：AlarmManagerService、PowerManagerService、AudioService等，这些服务在手机系统启动时就进行开启或监听状态，由ServiceManager负责实例化运行。系统服务与本地新增的服务属于两个不同进程，必须通过AIDL(Android Interface Definition Language ：Android接口定义语言)进行跨进程通信

二、新增具体案例

2.1 创建AIDL接口文件

路径：frameworks/base/core/java/android/service/test/IMyTestManager.aidl

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package android.service.test;
interface IMyTestManager {
String sayHello();
int priFunction();
}

package android.service.test;interface IMyTestManager {    String sayHello();    int priFunction();}

2.2 将创建的AIDL加入编译中

路径：frameworks/base/Android.mk

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## READ ME: ########################################################
##
## When updating this list of aidl files, consider if that aidl is
## part of the SDK API. If it is, also add it to the list below that
## is preprocessed and distributed with the SDK. This list should
## not contain any aidl files for parcelables, but the one below should
## if you intend for 3rd parties to be able to send those objects
## across process boundaries.
##
## READ ME: ########################################################
LOCAL_SRC_FILES += \
…
core/java/android/service/test/IMyTestManager.aidl \
…

## READ ME: ########################################################

#### When updating this list of aidl files, consider if that aidl is## part of the SDK API. If it is, also add it to the list below that## is preprocessed and distributed with the SDK. This list should## not contain any aidl files for parcelables, but the one below should## if you intend for 3rd parties to be able to send those objects## across process boundaries.#### READ ME: ########################################################LOCAL_SRC_FILES += \...core/java/android/service/test/IMyTestManager.aidl \...

2.2.1 注释的大概意思：

当更新这个文件列表时,如果考虑aidl是SDK API的一部分。如果它是，同时添加到下面的列表进行预处理和分布式的SDK。这个列表不包含任何aidl文件parcelables接口。但是如果你想让第三方能够在整个过程发送这些对象的话，你就应该下面有一个的目标

2.2.2 LOCAL_SRC_FILES += \ 这个宏是编译管理AIDL的，很多系统AIDL在此添加进行编译

2.2.3 在frameworks/base/下用mm进行单编，把AIDL的java接口生成出来

编译完成后检查路径：

out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/service/test/IMyTestManager.java

2.3 创建新的系统服务类

路径：frameworks/base/core/java/android/service/test/MyTestManagerService.java

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public class MyTestManagerService extends IMyTestManager.Stub{
private static final String TAG = “MyTestManagerService”;
private Context mContext;
public MyTestManagerService(Context context) {
mContext = context;
}
@Override
public String sayHello() throws RemoteException {
// TODO Auto-generated method stub
Log.d(TAG, ”sayHello()”);
return “Hello AIDL”;
}
@Override
public int priFunction() throws RemoteException {
// TODO Auto-generated method stub
Log.d(TAG, ”priFunction()”);
return 0;
}
}

public class MyTestManagerService extends IMyTestManager.Stub{    private static final String TAG = "MyTestManagerService";    private Context mContext;    public MyTestManagerService(Context context) {        mContext = context;    }    @Override    public String sayHello() throws RemoteException {        // TODO Auto-generated method stub        Log.d(TAG, "sayHello()");        return "Hello AIDL";    }    @Override    public int priFunction() throws RemoteException {        // TODO Auto-generated method stub        Log.d(TAG, "priFunction()");        return 0;    }}

2.4 创建系统服务公开接口管理类

路径：frameworks/base/core/java/android/service/test/MyTestManager.java

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public class MyTestManager {
private static final String TAG = “MyTestManager”;
private IMyTestManager mService;
public MyTestManager(IMyTestManager service) {
mService = service;
}
public String sayHello() throws RemoteException {
Log.d(TAG, ”sayHello()”);
return mService.sayHello();
}
}

public class MyTestManager {    private static final String TAG = "MyTestManager";    private IMyTestManager mService;    public MyTestManager(IMyTestManager service) {        mService = service;    }    public String sayHello() throws RemoteException {        Log.d(TAG, "sayHello()");        return mService.sayHello();    }}

2.4.1 Android系统中很多系统服务API没有全部公开，都是在Frameworks层通过Manager类封装一层来进行管理公开接口。也就是说对Application层公开都是通过Manager封装来决定的，这里我只公开了sayHello()。priFunction()是我故意不公开的，方便理解

2.5 将创建的服务添加进ServiceManager

路径：frameworks/base/services/java/com/android/server/SystemServer.java

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private void startOtherServices() {
…
AudioService audioService = null;
MyTestManagerService mTestService = null;
…
if (!disableMedia && !“0”.equals(SystemProperties.get(“system_init.startaudioservice”))) {
try {
Slog.i(TAG, ”Audio Service”);
audioService = new AudioService(context);
ServiceManager.addService(Context.AUDIO_SERVICE, audioService);
} catch (Throwable e) {
reportWtf(”starting Audio Service”, e);
}
}
…
try {
Slog.i(TAG, ”MyTestManager Service”);
mTestService = new MyTestManagerService(context);
ServiceManager.addService(Context.MYTEST_SERVICE, mTestService);
} catch (Throwable e) {
reportWtf(”starting MyTestManager”, e);
}
…
}

private void startOtherServices() {    ...    AudioService audioService = null;    MyTestManagerService mTestService = null;    ...    if (!disableMedia && !"0".equals(SystemProperties.get("system_init.startaudioservice"))) {        try {            Slog.i(TAG, "Audio Service");            audioService = new AudioService(context);            ServiceManager.addService(Context.AUDIO_SERVICE, audioService);        } catch (Throwable e) {            reportWtf("starting Audio Service", e);        }    }    ...    try {        Slog.i(TAG, "MyTestManager Service");        mTestService = new MyTestManagerService(context);        ServiceManager.addService(Context.MYTEST_SERVICE, mTestService);    } catch (Throwable e) {        reportWtf("starting MyTestManager", e);    }    ...}

2.5.1 为了阅读思路清晰，我保留了AudioService的服务添加代码。至于if条件，我们也可以添加，java里面控制的话可以在config.xml中定义bool类型，一般是为了区分多个项目的差异。涉及到项目的overlay，可根据操作项目的具体需求来进行。驱动底层一般都是宏控，稍微提一下。

2.5.2 代码中的Context.MYTEST_SERVICE服务常量添加

路径：frameworks/base/core/java/android/content/Context.java

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…
/**
* Use with {@link #getSystemService} to retrieve a
* {@link android.media.AudioManager} for handling management of volume,
* ringer modes and audio routing.
*
* @see #getSystemService
* @see android.media.AudioManager
*/
public static final String AUDIO_SERVICE = “audio”;
public static final String MYTEST_SERVICE = “mytest”;
…

.../*** Use with {@link #getSystemService} to retrieve a* {@link android.media.AudioManager} for handling management of volume,* ringer modes and audio routing.** @see #getSystemService* @see android.media.AudioManager*/public static final String AUDIO_SERVICE = "audio";public static final String MYTEST_SERVICE = "mytest";...

2.6 注册服务

路径：frameworks/base/core/java/android/app/ContextImpl.java

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static {
…
registerService(AUDIO_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
return new AudioManager(ctx);
}
});
registerService(MYTEST_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
IBinder iBinder = ServiceManager.getService(Context.MYTEST_SERVICE);
if (iBinder == null) {
return null;
}
IMyTestManager service = IMyTestManager.Stub
.asInterface(iBinder);
return new MyTestManager(service);
}
});
…
}

static {    ...    registerService(AUDIO_SERVICE, new ServiceFetcher() {        public Object createService(ContextImpl ctx) {            return new AudioManager(ctx);        }    });    registerService(MYTEST_SERVICE, new ServiceFetcher() {        public Object createService(ContextImpl ctx) {            IBinder iBinder = ServiceManager.getService(Context.MYTEST_SERVICE);                if (iBinder == null) {                    return null;                }                IMyTestManager service = IMyTestManager.Stub                    .asInterface(iBinder);                return new MyTestManager(service);            }    });    ...}

2.6.1 在这里可以看到明显的对比，有一个差异就是AudioManager在注册服务的时候并没有像我添加的一样将服务传给IBinder，再通过IBinder来进行接口对接获取到服务。其实，AudioManger已经在内部类做了这层封装，原理是一样的，也有很多系统服务采用我这种方式进行注册。附AudioManager部分源码：

路径：frameworks/base/media/java/android/media/AudioManager.java

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public class AudioManager {
…
private static IAudioService sService;
/**
* @hide
*/
public AudioManager(Context context) {
mContext = context;
…
}
private static IAudioService getService()
{
if (sService != null) {
return sService;
}
IBinder b = ServiceManager.getService(Context.AUDIO_SERVICE);
sService = IAudioService.Stub.asInterface(b);
return sService;
}
…
}

public class AudioManager {    ...    private static IAudioService sService;    /**     * @hide     */    public AudioManager(Context context) {        mContext = context;        ...    }    private static IAudioService getService()    {        if (sService != null) {            return sService;        }        IBinder b = ServiceManager.getService(Context.AUDIO_SERVICE);        sService = IAudioService.Stub.asInterface(b);        return sService;    }    ...}

2.7 调用新增的系统服务

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MyTestManager mTestManager = (MyTestManager) getSystemService(Context.MYTEST_SERVICE);
try {
//这里调用不出priFunction()，MyTestManager没有对它进行再次封装
mTestManager.sayHello();
} catch (RemoteException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

MyTestManager mTestManager = (MyTestManager) getSystemService(Context.MYTEST_SERVICE);try {    //这里调用不出priFunction()，MyTestManager没有对它进行再次封装    mTestManager.sayHello();} catch (RemoteException e) {    // TODO Auto-generated catch block    e.printStackTrace();}

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