Hazard pointer, epoch-based reclamation क्या है?

In a lock-free structure whose nodes are freed, a node removed by one thread may still be read by another that loaded its address before the removal. A hazard pointer is a per-thread published pointer to a node the thread is about to read; a node is freed only when no hazard pointer points to it (Michael, 2004). In epoch-based reclamation threads announce entering and leaving a global epoch; a node removed in epoch $e$ is freed once every thread has left $e$ (Fraser, 2004).