As it so happens, object lifetime tracking (or Memory Reclamation as I prefer to call it) is the current most difficult open problem in shared memory concurrency. If you want to design or implement a lock-free or wait-free data structure, the hardest part isn’t designing/implementing the data structure itself. The hardest task is to add memory reclamation to this data structure, without reducing the progress or throughput of the data structure you designed/implemented.

source: HN