1.java系统服务初识-vibrate

MrPeng1991

已于 2023-02-19 12:24:16 修改

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分类专栏：系统服务文章标签： android

于 2022-04-15 00:24:17 首次发布

本文链接：https://blog.youkuaiyun.com/gangjindianzi/article/details/124185372

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文章目录

1. 一个简单的系统服务
2. 从底层网上看
3. 从上层往下看
4 系统服务和应用通信

1. 一个简单的系统服务

//应用侧
Vibrator mVibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
mVibrator.vibrate(500);
//frameworks/base/core/java/android/app/ContextImpl.java
@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}
//frameworks/base/core/java/android/app/SystemServiceRegistry.java
 public static Object getSystemService(ContextImpl ctx, String name) {
    //SYSTEM_SERVICE_FETCHERS是一个HashMap，何时put？静态方法registerService中
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}
//===============
private static <T> void registerService(String serviceName, Class<T> serviceClass,
        ServiceFetcher<T> serviceFetcher) {
    SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
    SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}

//再看registerService   register了很多服务
static {
    registerService(Context.ACCESSIBILITY_SERVICE, AccessibilityManager.class,
            new CachedServiceFetcher<AccessibilityManager>() {
        @Override
        public AccessibilityManager createService(ContextImpl ctx) {
            return AccessibilityManager.getInstance(ctx);
        }});

    ...
    registerService(Context.VIBRATOR_SERVICE, Vibrator.class,
            new CachedServiceFetcher<Vibrator>() {
        @Override
        public Vibrator createService(ContextImpl ctx) {
            return new SystemVibrator(ctx);
        }});
    ...
}
//以上，getSystemService->registerService->static
//SystemVibrator .java
private final IVibratorService mService;
public SystemVibrator() {
    ...
    mService = IVibratorService.Stub.asInterface(
            ServiceManager.getService("vibrator"));
}

public boolean hasVibrator() {
    ...
    try {
        return mService.hasVibrator();
    } catch (RemoteException e) {
    }
    ...
}
//frameworks/base/core/java/android/os/IVibratorService.aidl
interface IVibratorService
{
    boolean hasVibrator();
    void vibrate(...);
    void vibratePattern(...);
    void cancelVibrate(IBinder token);
}
public class VibratorService extends IVibratorService.Stub

SystemVibrator构造函数中获取远程服务，VibratorService实现了IVibratorService定义的所有接口，并通过JNI调用到native层，进行更底层的实现.VibratorService是怎么注册为系统服务的呢

//SystemServer.java中
VibratorService vibrator = null;
...
//实例化VibratorService并添加到ServiceManager
traceBeginAndSlog("StartVibratorService");
vibrator = new VibratorService(context);
ServiceManager.addService("vibrator", vibrator);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
...
//通知服务系统启动完成
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "MakeVibratorServiceReady");
try {
    vibrator.systemReady();
} catch (Throwable e) {
    reportWtf("making Vibrator Service ready", e);
}
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

//这样在SystemVibrator里就可以通过下面的代码连接到VibratorService，与底层的系统服务进行通信了
IVibratorService.Stub.asInterface(ServiceManager.getService("vibrator"));

mService相当于IVibratorService在应用层的一个代理，所有的实现还是在SystemServer的VibratorService里。
看代码时可以发现registerService是在static代码块里静态调用的，所以getSystemServcr获得的各个Manager也都是单例的。

2. 从底层网上看

2.1 定义一个AIDL接口文件IVibratorService

frameworks/base/core/java/android/os/IVibratorService.aidl

2.2 定义服务VibratorService

frameworks/base/services/java/com/android/server/VibratorService.java

public class VibratorService extends IVibratorService.Stub

2.3将VibratorServicey添加到系统服务

// frameworks/base/services/java/com/android/server/SystemServer.java
VibratorService vibrator = null;
...
//实例化VibratorService并添加到ServiceManager
Slog.i(TAG, "Vibrator Service");
vibrator = new VibratorService(context);
ServiceManager.addService("vibrator", vibrator);
...
//通知服务系统启动完成
try {
    vibrator.systemReady();
} catch (Throwable e) {
    reportWtf("making Vibrator Service ready", e);
}

2.4 SystemVibrator

在SystemVibrator中构造方法通过IVibratorService的代理连接到VibratorService，这样SystemVibrator的接口实现里就可以调用IVibratorService的接口：

//frameworks/base/core/java/android/os/SystemVibrator.java
private final IVibratorService mService;
...
public SystemVibrator() {
    ...
    mService = IVibratorService.Stub.asInterface(
            ServiceManager.getService("vibrator"));
    ...
    public boolean hasVibrator() {
        ...
        try {
            return mService.hasVibrator();
        } catch (RemoteException e) {
        }
        ...
    }
}

2.5 getSystemService

//frameworks/base/core/java/android/app/ContextImpl.java
@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}
//frameworks/base/core/java/android/app/SystemServiceRegistry.java
 public static Object getSystemService(ContextImpl ctx, String name) {
    //SYSTEM_SERVICE_MAP是一个HashMap，何时put？
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}

2.6 SystemVibrator 实例化

//以上，getSystemService->registerService->static
//SystemServiceRegistry
private static <T> void registerService(String serviceName, Class<T> serviceClass,
        ServiceFetcher<T> serviceFetcher) {
    SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
    SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}
static {
    ...
    registerService(Context.VIBRATOR_SERVICE, Vibrator.class,
            new CachedServiceFetcher<Vibrator>() {
        @Override
        public Vibrator createService(ContextImpl ctx) {
            return new SystemVibrator(ctx);
        }});
    ...
}

2.7 上层调用

Vibrator mVibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
mVibrator.vibrate(500);

2.8 编译

frameworks/base/Android.mk 将AIDL文件添加到编译配置里

LOCAL_SRC_FILES += \
...
core/java/android/os/IVibratorService.aidl \

3. 从上层往下看

3.1app 调用接口

Vibrator mVibrator = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
mVibrator.vibrate(500);

3.2 getSystemService

//frameworks/base/core/java/android/app/ContextImpl.java
@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}
//frameworks/base/core/java/android/app/SystemServiceRegistry.java
 public static Object getSystemService(ContextImpl ctx, String name) {
    //SYSTEM_SERVICE_MAP是一个HashMap，何时put？
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}

3.3 SystemVibrator 实例化

//以上，getSystemService->registerService->static
//SystemServiceRegistry
private static <T> void registerService(String serviceName, Class<T> serviceClass,
        ServiceFetcher<T> serviceFetcher) {
    SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
    SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}
static {
    ...
    registerService(Context.VIBRATOR_SERVICE, Vibrator.class,
            new CachedServiceFetcher<Vibrator>() {
        @Override
        public Vibrator createService(ContextImpl ctx) {
            return new SystemVibrator(ctx);
        }});
    ...
}

3.4调用IVibratorService的接口

在SystemVibrator中通过IVibratorService的代理连接到VibratorService，这样SystemVibrator的接口实现里就可以调用IVibratorService的接口：

private final IVibratorService mService;
...
public SystemVibrator() {
    ...
    mService = IVibratorService.Stub.asInterface(
            ServiceManager.getService("vibrator"));
    ...
    public boolean hasVibrator() {
        ...
        try {
            return mService.hasVibrator();
        } catch (RemoteException e) {
        }
        ...
    }
}

3.5定义一个AIDL接口文件`IVibratorService`

frameworks/base/core/java/android/os/IVibratorService.aidl

3.6定义服务VibratorService，

实现IVibratorService定义的接口

public class VibratorService extends IVibratorService.Stub

3.7VibratorService添加到系统服务

VibratorService vibrator = null;
...
//实例化VibratorService并添加到ServiceManager
Slog.i(TAG, "Vibrator Service");
vibrator = new VibratorService(context);
ServiceManager.addService("vibrator", vibrator);
...
//通知服务系统启动完成
try {
    vibrator.systemReady();
} catch (Throwable e) {
    reportWtf("making Vibrator Service ready", e);
}

总结下
![在这里插入图片描述](https://img-blog.csdnimg.cn/3a7819703d124852bb1b3cea0ff59892.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBATXJQZW5nMTk5MQ==,size_20,color_FFFFFF,t_70,g_se,x_16
如需扩展接口

在IVibratorService添加接口；
在VibratorService添加接口的实现；
在Vibrator及SystemVibrator里扩展新的接口；

4 系统服务和应用通信

上面的实现我们看到的只是从应用层通过服务代理，调用系统服务的接口，如果我们想反过来，将系统服务的状态通知给应用层，该怎么做呢？

使用Broadcast

使用Broadcast广播可以实现跨进程的消息传递，一些系统服务也使用了这种方法。如电池管理服务BatteryManagerService，收到底层上报的电池状态变化信息时，就将当前的电池状态封装在一个Intent里，action为android.intent.action.BATTERY_CHANGED。应用只要注册一个对应的BroadcastReceiver就可以收到BatterManagerService发送的电池状态信息。