chenguangshen / android-helloworldservice Goto Github PK

Dummy native binder android HelloWorld sample created to better understand
the possibilities of creating pure native android services. The current
status is that it certainly is possible to create native binder services
under Android

Scope:
We are currently mostly interested in creating a native service started from
init.rc and we would like this service to be pure native (no JVM). We want
this service to act as much as possible like any other android service. We
would also like it to be possible for the client of the service to not depend
on Android internal API's.

Limitations:
The native service currently runs as system user and uses the
ServiceManager.addService('name',binder) method. This method is not available
to normal packages installed on a stock phone. For that limitation to be
worked around it it probably is needed to let the android system (ActivityManager?)
let create the IBinder object and pass it to the native


On the following thread Dianne Hackborn states
https://groups.google.com/d/topic/android-porting/yK17XZXkupI/discussion

 The Java runtime has wrappers around C++ IBinder.  This is what Java's Binder is.
 You can write a JNI function that returns a Java Binder and in its implementation
 instantiate a C++ IBinder interface and return it.  You will need to use this magic
 function in libandroid_runtime to do this:

  extern jobject javaObjectForIBinder(JNIEnv* env, const sp<IBinder>& val);
 The header for this is currently in core/jni/android_util_Binder.h.

It will be probably nececary to pass a Binder object created to the native code.
An other problem might be related to the threading

This code was taken from http://github.com/mcr/Android-HelloWorldService and
modified to work on gingerbread.

Reading the code:

Best is to start reading  libhelloworldservice/include/IHelloWorld.h comparing it to the code generated by aidl
and follow with native implementations of that interface
libhelloworldservice/src/helloworldservice.cpp
libhelloworldservice/src/helloworldclient.cpp

After that read the native "server" code helloworld/main_helloworldservice.cpp to see how the native code works

to Find the usage read AndroidManifest.xml src/org/credil/helloworldservice/HelloWorldActivity.java and star fix code in
src/org/credil/helloworldservice/HelloWorldService.java :P


Building/playing around:

For information about developing "inside" Android
https://github.com/keesj/gomo/wiki/AndroidPlatformDevelopmentWorkflow

Checkout this this branch into your android platform tree
. build/envsetup.sh
lunch sdk-eng
make


After that 
and goto the Android-HelloWorldService directory
use mm/adb sync to build deploy

Running:

From the shell:
# /system/bin/helloworldservice
hello: fun
hello: Using interfaces
hello: Calling from Java now

# /system/bin/helloworldclient

To launch the Activity use the activity launcher.


Native binder:
/* Interfaces extend */
class IInterface extends RefBase
    + asBinder()
    + onAsBinder();

/* The native class implementation extends BnInterface
 * this is the instance that will be given to the service
 * manager
 *
 * BnInterface is the base implementation for a native (local) IInterface
 **/
class BnInterface<INTERFACE> extends BBinder
    + queryLocalInterface(descriptor)

/**
 * The BBinder class is the standard implementation of IBinder for a IInterface object
 **/
class BBinder extends IBinder
    + getInterfaceDescriptor()
    + attachObject(id ...) /* housekeeping of clients? */
    + findObject(id ...)
    + detachObject(id ...);

/* remote stub implemntation extends */
class BpInterface<INTERFACE> extends BpRefBase
    + onAsBinder();



/* BpRefBase defines a ref counted class having a method to get
 * a binder object
 */
class BpRefBase extends RefBase
    + remote() IBinder*