How python stop-the-world when gc handling reference cycles?

Question

Is python gc.collect() a stop-the-world (STW) garbage collector?

If it is a STW garbage collector, where and when to stop the world?

I know python uses deterministic reference counting, and this do not need stop the world. However, when handling the cycles, does python need stop the world?

Answer 1

IMO it is indeed the STW garbage collector in CPython. Because each thread is required to acquire GIL before it runs, and GIL is never released in the cycle-finding routine (quote from PEP-703).