bpo-32309: Add support for contextvars in asyncio.to_thread() (GH-20278)
Allows contextvars from the main thread to be accessed in the separate thread used in `asyncio.to_thread()`. See the [discussion](https://github.com/python/cpython/pull/20143#discussion_r427808225) in GH-20143 for context.
Automerge-Triggered-By: @aeros
diff --git a/Lib/asyncio/threads.py b/Lib/asyncio/threads.py
index 2f40467..51e0ba9 100644
--- a/Lib/asyncio/threads.py
+++ b/Lib/asyncio/threads.py
@@ -1,6 +1,7 @@
"""High-level support for working with threads in asyncio"""
import functools
+import contextvars
from . import events
@@ -12,10 +13,13 @@
"""Asynchronously run function *func* in a separate thread.
Any *args and **kwargs supplied for this function are directly passed
- to *func*.
+ to *func*. Also, the current :class:`contextvars.Context` is propogated,
+ allowing context variables from the main thread to be accessed in the
+ separate thread.
Return an asyncio.Future which represents the eventual result of *func*.
"""
loop = events.get_running_loop()
- func_call = functools.partial(func, *args, **kwargs)
+ ctx = contextvars.copy_context()
+ func_call = functools.partial(ctx.run, func, *args, **kwargs)
return await loop.run_in_executor(None, func_call)