Hi, I have a class (for illustrative purpose only): class X { public: X() : id_(0) // does not compile { } void f() { if (operation_failed) id_ = 0; // does not compile else id_ = boost::this_thread::get_id(); // get which thread is sucessfully executing f() } bool compare() { // compare current thread with the one that has sucessfully executed f() return id_ == boost::this_thread::get_id(); } private: boost::thread::id id_; }; My questions are: How can I set the id_ to an initial value (e.g., 0 here) for compare() function to get correct result, assuming multiple threads might be executing f() and compare() at the same time? Is there a way to do this: atomicboost::thread::id id_; to make them thread-safe? Thanks a lot in advance, Robert