android ndk

Question

我正在尝试在曲面上渲染视频，当我尝试在渲染过程中更改渲染曲面但应用程序因渲染循环中的mNativeSurface = NULL而崩溃。我做错了什么

Decoder.h

class Decoder {
private:
    ANativeWindow* mNativeSurface;
    static void* threadStartCallback(void *myself);
    pthread_mutex_t _mutex_window;
public:
    void changeSurface(JEnv* env,jobject surface);


}

Decoder.cpp

class Decoder{
    public Decoder(JEnv* env,jobject surface){
        pthread_mutex_init(&_mutex_window, 0);
        mNativeSurface= ANativeWindow_fromSurface(env,surface);
       // create a thread and pass surface as widow
        pthread_create(&_threadId, 0, threadStartCallback, this);

    }

    void changeSurface(JEnv* env,jobject surface){
     //after some time i am changinf surface
       pthread_mutex_lock(&_mutex_window);
       mNativeSurface= ANativeWindow_fromSurface(env,surface);
       pthread_mutex_unlock(&_mutex_window);    

    }

    void* Decoder::threadStartCallback(void *myself)
    {
        while(/* condition */){
        //When i change surface while loop in sleep
         pthread_mutex_lock(&_mutex_window);
            Rendering on mNativeSurface //rendering ----
         pthread_mutex_unlock(&_mutex_window);

           /*
            *Decoding + Rendering in while loop
            */      
        } 
        return 0;
    }
}

提前致谢。