Create event loop when needed, and shut it down afterwards.

This fixes issues with the tests (no more "unclosed event loops"
errors), and probably allows tee_popen() to run in parallel.

Author: felixfontein

nox/_cli.py

@@ -17,7 +17,6 @@
 from __future__ import annotations
 
 __lazy_modules__ = {
-    "asyncio",
     "importlib",
     "importlib.metadata",
     "nox._options",
@@ -37,7 +36,6 @@
     "urllib.parse",
 }
 
-import asyncio
 import importlib.metadata
 import os
 import shutil
@@ -318,7 +316,6 @@ def _main(*, main_ep: bool) -> None:
                 )
 
     nox.registry.reset()
-    asyncio.set_event_loop(asyncio.new_event_loop())
     exit_code = execute_workflow(args)
 
     # Done; exit.

nox/popen.py

@@ -170,11 +170,10 @@ class _TeeSubprocess:
     def __init__(
         self,
         *,
-        loop: asyncio.AbstractEventLoop,
         interrupt_timeout: float | None,
         terminate_timeout: float | None,
     ) -> None:
-        self.loop = loop
+        self.loop = asyncio.new_event_loop()
         self.stdout: list[bytes] = []
         self.stderr: list[bytes] = []
         self.interrupt_timeout = interrupt_timeout
@@ -353,6 +352,7 @@ def handle_sigint() -> None:
             )
         finally:
             self.loop.remove_signal_handler(signal.SIGINT)
+            self.loop.close()
         sys.stdout.flush()
         if is_canceled:
             raise KeyboardInterrupt
@@ -371,9 +371,7 @@ def tee_popen(
     Return a tuple ``(return_code, stdout, stderr)``.
     Standard output and standard error are also printed to ``sys.stdout``.
     """
-    loop = asyncio.get_event_loop()
     teesub = _TeeSubprocess(
-        loop=loop,
         interrupt_timeout=interrupt_timeout,
         terminate_timeout=terminate_timeout,
     )