Hello, here is a simplified code I wrote: class A{ public: A(); ~A(); void Run(); void ThreadA(); virtual void HandleSomething(); }; void A::HandleSomething() { } void A::ThreadA() { if(condition) { HandleSomething(); } } void A::Run() { boost::thread thread(&A::ThreadA,this); } This is my base class. As you can see the thread calls the virtual function when the condition becomes true. I use the virtual function in my derived class so everytime the condition becomes true the function HandleSomething() should do something. So far, so good but when I try to change some variables in the derived class the program crashes without any warning or error message. I use the latest Ubuntu version with GCC 4.5.3 and boost 1.46.1.