pure virtual method called in thread of concrete class

Question

I have a problem with virtual methods in C++ on a multithreading context (Linux).

This next example points out my problem:

class Base {

};

class Concrete1: public Base {    //define pure virtual function
    virtual void func() = 0;
}; 

class Concrete2: public Concrete1 {     //override of virtual func
    void func() {}

    void run(){
        //....
        pthread_create(&handle, NULL, Concrete2::thread, static_cast<void*>(this));
    }

    static void* thread(void arg*){
        Concrete2 *ptr = static_cast<Concrete2*>(arg);
        //Concrete1 *ptr = static_cast<Concrete2*>(arg);    // same error 

        while(1){ 
           //....
           ptr->func()
        }
    }
};

int main(){
  Concrete2 obj;
  obj.run();

  pthread_exit(NULL);
  return 0;
}

When the line ptr->func() is executed, the following error appears:

pure virtual method called terminate called without an active exception

Can someone tell me why the pure virtual method is being called instead of the overrided method?

Answer 1

Concrete2 is created on the stack and is destroyed as soon as run is called.

The spawned thread does not keep obj alive.

Your thread function is trying to dereference a destroyed object, aka a dangling pointer , which constitutes undefined behavior.