How native function is called in…

How native function is called in Android platform ( unfinished version)

1.  Power.java --> find corresponding native c file

          android.os.Power.java -------- native file ----> .../jni/android_os_Power.c

 

2. in android_os_Power.c, you can find:

 

static JNINativeMethod method_table[] =   // Native function table

{
    { "acquireWakeLock", "(ILjava/lang/String;)V", (void*)acquireWakeLock },
    { "releaseWakeLock", "(Ljava/lang/String;)V", (void*)releaseWakeLock },
    { "setLastUserActivityTimeout", "(J)I", (void*)setLastUserActivityTimeout },
    { "setScreenState", "(Z)I", (void*)setScreenState },
    { "shutdown", "()V", (void*)android_os_Power_shutdown },
    { "reboot", "(Ljava/lang/String;)V", (void*)android_os_Power_reboot },
};

 

int register_android_os_Power(JNIEnv *env) // function to register mapping table from name to function
{
    return AndroidRuntime::registerNativeMethods(
        env, "android/os/Power",
        method_table, NELEM(method_table));
}

3. in /framework/base/core/jni , a file named: AndroidRuntime.cpp

 

    3.1) a global register function array

            static const RegJNIRec gRegJNI[] =

            {

                      ...

                      register_android_os_Power,

           }

 

    3.2) Register native function process

                   int AndroidRuntime::startReg(JNIEnv* env)

           or

                  Java_com_android_internal_util_WithFramework_registerNatives(...)

           or

                 Java_LoadClass_registerNatives(....)

                   ---> register_jni_procs(gRegJNI, NELEM(gRegJNI), env)

                           ---> foreach(member of gRegJNI)  call register_XXX_XXX_XXX..XXX()  // so here register_android_os_power() will be called

                                   ---> AndroidRuntime::registerNativeMethods(env, class_name like "android/os/Power", method table like method_table, size)

                                          ---> jniRegisterNativeMethods(env, className, gMethods, numMethods)

                                                  --> pEnv->RegisterNatives(env, clazz, gMethods, numMethods) ;

                                                        --> foreach(method) call dvmRegisterJNIMethod(ClassObject* clazz, const char* methodName,

                                                                                                                                     const char* signature, void* fnPtr) 

                                                              -->   call dvmSetNativeFunc(method, dvmCallSynchronizedJNIMethod, fnPtr); // for sycn method

                                                                  or

                                                                      call  dvmSetNativeFunc(method, dvmCallJNIMethod, fnPtr);

                                                                      -->    ((Method*)method)->insns = insns; // set actual code space to be executed for a native function

      

4. calling a native method ( JNI method)

    void dvmPlatformInvoke(void* pEnv, ClassObject* clazz, int argInfo, int argc,
    const u4* argv, const char* shorty, void* func, JValue* pReturn)

    dvmCallMethod() /dvmInvokeMethod

     --->     if (dvmIsNativeMethod(method))

         {
                   (*method->nativeFunc)(self->curFrame, &retval, method, self);
         }