Android 中Native方法是怎样调用的

FROM:http://blog.csdn.net/a379039233/article/details/6097651

1.Power.java--> find corresponding native cfile（查找对应的具体用C实现的C文件）

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

2. in android_os_Power.c, you canfind:

static JNINativeMethod method_table[]= // Native functiontable
{
    {"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 tablefrom name
  //to function
{
    returnAndroidRuntime::registerNativeMethods(
       env, "android/os/Power",
       method_table, NELEM(method_table));
}

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

   1) a global register function array

static const RegJNIRec gRegJNI[] =
           {
                    // ...
                     register_android_os_Power,
          }

   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 becalled
    ---> AndroidRuntime::registerNativeMethods(env,
                           /*class_namelike */"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,
                                                  constchar* signature, void* fnPtr)
    ---> call dvmSetNativeFunc(method, dvmCallSynchronizedJNIMethod, fnPtr);
                                                   //for sycn method
    or
    call dvmSetNativeFunc(method, dvmCallJNIMethod,fnPtr);
    ---> ((Method*)method)->insns = insns;
    // set actual codespace 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);
   }