How are greenlets implemented? Python uses the C stack for the interpreter and it heap-allocates Python stack frames, but beyond that, how does it allocate/swap stacks, how does it hook into the interpreter and function call mechanisms, and how does this interact with C extensions? (Any quirks)?
There are some comments at the top of greenlet.c in the source, but they're a bit opaque. FWIW I'm coming from the perspective of someone who is unfamiliar with CPython internals but is very familiar with low-level systems programming, C, threads, events, coroutines/cooperative threads, kernel programming, etc.
(Some data points: they don't use ucontext.h and they do 2x memcpy, alloc, and free on every context switch.)