Android 中Native方法是怎样调用的

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.c

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

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) callregister_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) calldvmRegisterJNIMethod(ClassObject* clazz, const char*methodName,
constchar* signature, void* fnPtr)
--> calldvmSetNativeFunc(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);

}