The binder for Android Analytics 02

Analyze the Java layer's ServiceManager to see how binder is implemented in the Java layer.

Public final class ServiceManager {    private static final String TAG = "ServiceManager";    private static Iservicemanager Sservicemanager;//iservicemanager is an interface that defines a common (public) method.    private static hashmap<string, ibinder> Scache = new hashmap<string, ibinder> ();//cache, its value is IBinder ... Public    static IBinder GetService (String name) {        try {            IBinder service = scache.get (name);//First find if from cache            ( Service! = null) {                return service;            } else {                return Getiservicemanager (). GetService (name);//Generate a new IBinder            }        } catch (RemoteException e) {            log.e (TAG, "Error in GetService", e);        }        return null;    }
...

The ServiceManager here is just a package whose member variables and methods are static. From the above Scache saved key value pairs and GetService return value type IBinder (unlike the C + + layer IBinder) can be seen, through ServiceManager is a IBinder type object, through the analysis of the following, You can actually see that it is a Bpbinder object.

    private static Iservicemanager Getiservicemanager () {if (Sservicemanager! = null) {return sservice        Manager; }//Find the service Manager Sservicemanager = Servicemanagernative.asinterface (Binderinternal.getcontextob    Ject ());//Find Iservicemanager object and return to Sservicemanager;  } .../** * Return the Global "context object" of the system.     This is usually * a implementation of Iservicemanager, which you can use for Find * other services. */public static final native IBinder Getcontextobject ();//binderinternale: Call native function, return IBinder object ... static public I ServiceManager asinterface (IBinder obj)//Incoming is the IBinder object above, remember that this is the Java object {if (obj = = null) {return n        Ull } Iservicemanager in = (Iservicemanager) obj.querylocalinterface (descriptor);//Find from IBinder object and convert to IService        Manager Object if (in! = null) {return in; } return new Servicemanagerproxy (oBJ);//If not found, a Servicemanageporxy object is generated using the incoming IBinder object} 

Above a circle, directly from the Servicemanagerproxy view, there are two aspects: 1, get a native layer of an object, and converted to IBinder, that is, the above native IBinder Getcontextobject (); 2, Use the obtained ibinder to generate a Servicemanagerproxy object. Here's a look at how Servicemanagerproxy is constructed:

    Public Servicemanagerproxy (IBinder remote) {        Mremote = Remote;//mremote is the IBinder type, where the incoming IBinder object is saved in Mremote    }

    Public IBinder GetService (String name) throws RemoteException {        Parcel data = Parcel.obtain ();        Parcel reply = Parcel.obtain ();        Data.writeinterfacetoken (iservicemanager.descriptor);        Data.writestring (name);        Mremote.transact (get_service_transaction, data, reply, 0);//finally use IBinder's transact to transmit data        ibinder binder = Reply.readstrongbinder ();        Reply.recycle ();        Data.recycle ();        return binder;    }

Summary: Calling ServiceManager's GetService () generates a Servicemanagerproxy object that holds a mremote (IBinder), The Mremote (which is represented by the Bpbinder in the Java layer) can send data to the lower level.

Getcontextobject Analysis:

public static final native IBinder Getcontextobject ();//binderinternale: Call native function, return IBinder object-corresponds to this function:

Static Jobject Android_os_binderinternal_getcontextobject (jnienv* env, Jobject clazz) {    sp<ibinder> B = Processstate::self ()->getcontextobject (NULL);//Go here: B is a bpbinder    return Javaobjectforibinder (env, b);// Returns the binderproxy of a Java layer

Here we understand that the above Mremote hold the Binderproxy object. The Transact () method that calls the Mremote object above is the Transact method that calls Binderproxy:

    Public native Boolean transact (int code, PARCEL data, Parcel reply,            int flags) throws Remoteexception;...static Jboole An android_os_binderproxy_transact (jnienv* env, Jobject obj,        jint code, Jobject dataobj, Jobject replyobj, Jint flags )//Throws remoteexception{    if (dataobj = = null) {        jnithrownullpointerexception (env, NULL);        return jni_false;    }    parcel* data = Parcelforjavaobject (env, dataobj);    if (data = = NULL) {        return jni_false;    }    parcel* reply = Parcelforjavaobject (env, replyobj);    if (reply = = null && replyobj! = null) {        return jni_false;    }    ibinder* target = (ibinder*)//convert Binderproxy to Bpbinder        Env->getintfield (obj, gbinderproxyoffsets.mobject);
...
status_t err = target->transact (code, *data, reply, flags);//call Bpbinder to communicate with the lower layer ...

Come here: The Java layer is primarily to get the native layer of bpbinder, and use it to communicate with the underlying.

Binder for Android analytics