asyncio context propagation in Python 3.5/3.6 #71
Description
The contextvars approach to context propagation requires copying current context on asyncio task creation. This is done internally in asyncio for Python 3.7; however, on Python <3.7 context is not propagated automatically.
Example:
import asyncio
import contextvars
current_task = contextvars.ContextVar("current_task")
async def foo(foo_started, bar_done):
current_task.set("foo")
foo_started.set()
await bar_done.wait()
print("foo task:", current_task.get())
async def bar(foo_started, bar_done):
await foo_started.wait()
current_task.set("bar")
bar_done.set()
async def main():
foo_started = asyncio.Event()
bar_done = asyncio.Event()
await asyncio.gather(
foo(foo_started, bar_done),
bar(foo_started, bar_done),
)
loop = asyncio.get_event_loop()
loop.run_until_complete(main())In Python 3.7, the code above will print foo task: foo
In Python 3.5 and 3.6, the code above will print foo task: bar