The first year of free-threaded Python

> Instead, many reach for multiprocessing, but spawning processes is expensive

Agreed.

> and communicating across processes often requires making expensive copies of data

SharedMemory [0] exists. Never understood why this isn’t used more frequently. There’s even a ShareableList which does exactly what it sounds like, and is awesome.

[0]: https://docs.python.org/3/library/multiprocessing.shared_mem...

Processes can die independently so the state of a concurrent shared memory data structure when a process dies while modifying this under a lock can be difficult to manage. Postgres which uses shared memory data structures can sometimes need to kill all its backend processes because it cannot fully recover from such a state.

In contrast, no one thinks about what happens if a thread dies independently because the failure mode is joint.