SingleInstanceTask has distinct steps for creation of the object, and
starting the task. If a different coroutine is waiting on the
SingleInstanceTask, it isn't safe to directly call
SingleInstanceTask.wait() as the task may or may not have been created
yet.
Existing code usage of SingleInstanceTask is in 4 categories, with
reguards to SingleInstanceTask.wait():
1) using SingleInstanceTask without using SingleInstanceTask.wait().
This is unchanged.
2) using SingleInstanceTask.wait without a check on task is not None.
This may be safe now, but is fragile in the face of innocent-looking
refactors around the SingleInstanceTask.
3) using SingleInstanceTask.wait after confirming that the task is not
None. This is fine but a leaky abstraction.
4) directly waiting on the SingleInstanceTask.task. Another leaky
abstraction, but it's solving a cancellation problem. Leaving this
alone.
By enhancing SingleInstanceTask.wait(), cases 2 and 3 are improved. The
code not checking the task today is made safer, and the code checking
the task today can be simplified.
parameterized async tests run into cpython bug gh-101486
We use parameterized.expand, which works by creating new functions and
inserting those into the list of tests. It's a wonder this worked at
all before for the async tests.
Update the function generation to create a coroutine function, if
appropriate.
LP: #2007554
cancel_restart is a mode for SingleInstanceTask that changes the
behavior when starting the task - if the task is already running, do not
cancel it to start another.
Dan Bungert