Android SystemService的启动流程

SystemServer.java(由init进程起来)之后会调用：

mSystemServiceManager.startService(FingerprintService.class);

startService() 方法:

public <T extends SystemService> T startService(Class<T> serviceClass) {
final String name = serviceClass.getName();
Slog.i(TAG, "Starting " + name);

// Create the service.
if (!SystemService.class.isAssignableFrom(serviceClass)) {
throw new RuntimeException("Failed to create " + name
+ ": service must extend " + SystemService.class.getName());
}
final T service;
try {
Constructor<T> constructor = serviceClass.getConstructor(Context.class);
service = constructor.newInstance(mContext);
} catch (InstantiationException ex) {
throw new RuntimeException("Failed to create service " + name
+ ": service could not be instantiated", ex);
} catch (IllegalAccessException ex) {
throw new RuntimeException("Failed to create service " + name
+ ": service must have a public constructor with a Context argument", ex);
} catch (NoSuchMethodException ex) {
throw new RuntimeException("Failed to create service " + name
+ ": service must have a public constructor with a Context argument", ex);
} catch (InvocationTargetException ex) {
throw new RuntimeException("Failed to create service " + name
+ ": service constructor threw an exception", ex);
}

// Register it.
mServices.add(service);

// Start it.
try {
<strong><span style="font-size:24px;">service.onStart();//很关键的方法，会把自己添加到SystemManager中</span></strong>
} catch (RuntimeException ex) {
throw new RuntimeException("Failed to start service " + name
+ ": onStart threw an exception", ex);
}
return service;
}

onStart():

    @Override
    public void onStart() {
        publishBinderService(Context.FINGERPRINT_SERVICE, new FingerprintServiceWrapper());
        IFingerprintDaemon daemon = getFingerprintDaemon();
        if (DEBUG) Slog.v(TAG, "Fingerprint HAL id: " + mHalDeviceId);
        listenForUserSwitches();
    }

publishBinderService():

/**
* Publish the service so it is accessible to other services and apps.
*/
protected final void publishBinderService(String name, IBinder service,
boolean allowIsolated) {
ServiceManager.addService(name, service, allowIsolated);
}

//authenticate()为什么要用mhander.post 调用startAuthentication()方法，不可以直接调用

mHandler.post(new Runnable() {

@Override

public void run() {

startAuthentication(token, opId, effectiveGroupId, receiver, flags, restricted);

}

});