如何使用JNI管理C ++代码中的静态变量？

Question

My question is, Assume I have a c++ class with singleton and through JNI methods I call this singleton, does each time I call from java to c++ the singleton variable changed because its static, or it remains the same ? and does each time I call from java to c++ it run the method on new thread or no?

Example Code:

in Java:

class NativeLib
{
  public native void updateFrame();
}

in C/C++ :

JNIEXPORT void JNICALL Java_com_Company_NativeLib_NativeLib_updateFrame()
{
   sceneManager::getInstance()->updateFrame();
}

Does sceneManager::getInstance() at each call return new instance or the latest created instance since its a static variable.

my main problem in android my app crash without showing any kind of logCat information why it crashed.

but if I comment the sceneManager::getInstance()->updateFrame(); , it never crash so what I think is when ever Java make a call to C++ it is in a new thread which mean static variables does not

Answer 1

Think of the VM as a library of C/C++ code that your application has called into. Sometimes it calls back into your code.

Singletons will not be recreated -- it's just a method call. The Dalvik VM threads are just pthreads, and whichever thread executes the native call from Java-language code will be the thread that executes your C++ code.

Your best bet is to attach a native debugger. FWIW, one way to crash with nothing in logcat is to have native recursion that overflows the stack. Another way is to change the signal handlers for SIGSEGV / SIGBUS and friends.