Addresses two race conditions in background task runs #14115
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During reliability testing of background tasks, I kept experiencing hangs that couldn't be explained by task deadlocking due to the `limit` on the worker (see #14092). Here I'm addressing two causes of them: 1. Returning the first singleton instance of `TaskRunWaiter` before it is confirmed to be listening to the websocket. Using an `asyncio.Event` to signal that the socket is actually connected before proceeding. 2. When `PrefectDistributedFuture` was waiting for task runs to complete, it would ask the API if the task run was complete first, then go on to start waiting. If the task changed state in-between those calls, it would likely be missed entirely. With these changes in place, I've run a large number of my test tasks (see PrefectHQ/nebula#7962, which has a task with 5 layers of dependencies) at `TASKS=100` and have experienced no hangs. I did get a hang with `TASKS=1000`, but this is a marked improvement from where we were before. Part of #14098
chrisguidry
commented
Jun 18, 2024
| @@ -76,8 +77,9 @@ def __init__( | |||
| limit: Optional[int] = 10, | |||
| ): | |||
| self.tasks: List[Task] = list(tasks) | |||
| self.task_keys = set(t.task_key for t in tasks if isinstance(t, Task)) | |||
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The refactoring in this file is just to make the /status endpoint more useful and isn't part of the fix here
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During reliability testing of background tasks, I kept experiencing hangs that
couldn't be explained by task deadlocking due to the
limiton the worker (see#14092). Here I'm addressing two causes of them:
TaskRunWaiterbefore it isconfirmed to be listening to the websocket. Using an
asyncio.Eventtosignal that the socket is actually connected before proceeding.
PrefectDistributedFuturewas waiting for task runs to complete, itwould ask the API if the task run was complete first, then go on to start
waiting. If the task changed state in-between those calls, it would likely
be missed entirely.
With these changes in place, I've run a large number of my test tasks (see
PrefectHQ/nebula#7962, which has a task with 5 layers of dependencies) at
TASKS=100and have experienced no hangs. I did get a hang withTASKS=1000,but this is a marked improvement from where we were before.
Part of #14098