干货|JNI实现机制

so加载焦点历程：

class中当地要领加载历程：

当地要领挪用历程：

JNIEnv作用及实现

JNIEnv是JNI指针接口，通常我们通过它来挪用操作Java工具，它提供了所有的操作java工具的api。

那么JNIEnv又是何时建立，以及怎样来操作Java工具的呢？我们一起来看看它的详细实现~

首先我们来看下线程时怎样被建立的：

java/lang/Thread.java

new Thread().start() -> VMThread.create()

public synchronized void start() {

checkNotStarted();

hasBeenStarted = true;

VMThread.create(this, stackSize);// VMThread建立

}

/dalvik/vm/native/java_lang_VMThread.cpp

Dalvik_java_lang_VMThread_create() -> Thread.dvmCreateInterpThread()

const DalvikNativeMethod dvm_java_lang_VMThread[] = {

{ "create", "(Ljava/lang/Thread;J)V",

Dalvik_java_lang_VMThread_create },//线程建立要领

{ "currentThread", "()Ljava/lang/Thread;",

Dalvik_java_lang_VMThread_currentThread },

//……

};

static void Dalvik_java_lang_VMThread_create(const u4* args, JValue* pResult)

{

//……

dvmCreateInterpThread(threadObj, (int) stackSize);//建立线程

RETURN_VOID();

}

/dalvik/vm/Thread.cpp

dvmCreateInterpThread() -> interpThreadStart() -> jni.dvmCreateJNIEnv()

bool dvmCreateInterpThread(Object* threadObj, int reqStackSize)

{

//......

Thread* newThread = allocThread(stackSize);

//......

int cc = pthread_create(&threadHandle, &threadAttr, interpThreadStart, newThread);//建立线程

// ......

}

/*

* pthread entry function for threads started from interpreted code.

*/

static void* interpThreadStart(void* arg)

{

//......

self->jniEnv = dvmCreateJNIEnv(self);//建立jniEnv

//......

return NULL;

}

JNIEnv的建立

/dalvik/vm/jni.cpp

dvmCreateJNIEnv()

JNIEnv* dvmCreateJNIEnv(Thread* self) {

JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;

//……

newEnv->funcTable = &gNativeInterface;//接口函数

//......

return (JNIEnv*) newEnv;

}

static const struct JNINativeInterface gNativeInterface沈阳微信小程序

DefineClass,

FindClass,

//......

CallVoidMethod,

//...

GetFieldID,

GetObjectField,

//...

CallStaticIntMethod,

//......

};

//要领详细实现（下面是callVoidMethodA()详细实现）

CALL_VIRTUAL(_ctype, _jname, _retfail, _retok, _isref)

static _ctype Call##_jname##Method(JNIEnv* env, jobject jobj,

jmethodID methodID, ...)

{

ScopedJniThreadState ts(env);

Object* obj = dvmDecodeIndirectRef(ts.self(), jobj);

const Method* meth;

va_list args;

JValue result;

meth = dvmGetVirtualizedMethod(obj->clazz, (Method*)methodID);

if (meth == NULL) {

return _retfail;

}

va_start(args, methodID);

dvmCallMethodV(ts.self(), meth, obj, true, &result, args);//要领挪用

va_end(args);

if (_isref && !dvmCheckException(ts.self()))

result.l = (Object*)addLocalReference(ts.self(), result.l);

return _retok;

}

CALL_VIRTUAL(jobject, Object, NULL, (jobject) result.l, true);

//......

/dalvik/vm/interp/Stack.cpp

JNIEnv.CallVoidMethodA() -> Stack.dvmCallMethodA()

void dvmCallMethodA(Thread* self, const Method* method, Object* obj,

bool fromJni, JValue* pResult, const jvalue* args)

{

//......

if (dvmIsNativeMethod(method)) {

TRACE_METHOD_ENTER(self, method);

(*method->nativeFunc)((u4*)self->interpSave.curFrame, pResult,

method, self);//执行要领

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