Some GC detects cycles, some not (reference counting is example of GC which does not), but even those which detects cycles, may not able to detect all of them o

Some GC detects cycles, some not (reference counting is example of GC which does not), but even those which detects cycles, may not able to detect all of them or it can be expensive as, for example, in typical Mark&Sweep GC, because it may require to stop the world to perform GC, which is unacceptable for system programming languages, like C, C++, Rust.