Adds a "Future arch — what subints would buy us" section to
the module docstring, complementing the prior commit's
current-state rationale. Code is unchanged.
Frames the `subint` prefix as family-naming today (no actual
subinterp is created yet), then lays out the three concrete
wins that land once jcrist/msgspec#1026 unblocks PEP 684
isolated-mode subints:
- Cheaper forks — moving the parent's `trio.run()` into a
subint shrinks the main-interp COW image the child inherits.
The main interp becomes the literal forkserver: an
intentionally-empty execution ctx whose only job is to call
`os.fork()` cleanly.
- True parallelism — per-interp GIL means the forkserver
thread on main and the trio thread on subint actually run in
parallel. Spawn latency stops stalling the trio loop.
- Multi-actor-per-process — the architectural payoff. With
per-interp-GIL subints, one process can host main + N
subint-resident actor `trio.run()`s, and `os.fork()` reverts
to the last-resort spawn (only when OS-level isolation is
actually needed). Joins the story with the in-thread
`_subint.py` backend: `subint` → in-process spawn,
`subint_forkserver` → cross-process when a real OS boundary
is required.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
(cherry picked from commit 4b5176e2c3)
Gud Boi
f86c003567