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Will McGugan
2023-02-11 17:11:38 +00:00
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docs/blog/posts/create-task-psa.md
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@@ -15,7 +15,7 @@ I'm taking a brief break from blogging about [Textual](https://github.com/Textua
If you have ever used `asyncio.create_task` you may have created a bug for yourself that is challenging (read *almost impossible*) to reproduce. If it occurs, your code will likely fail in unpredictable ways. If you have ever used `asyncio.create_task` you may have created a bug for yourself that is challenging (read *almost impossible*) to reproduce. If it occurs, your code will likely fail in unpredictable ways.
The root cause of this [Heisenbug](Heisenbug) is that if you don't hold a reference to the task object returned by `create_task` then the task may simply disappear, without warning, when Python runs garbage collection. This behavior is [well documented](https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task), as you can see from this excerpt: The root cause of this [Heisenbug](Heisenbug) is that if you don't hold a reference to the task object returned by `create_task` then the task may simply disappear, without warning, when Python runs garbage collection. This behavior is [well documented](https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task), as you can see from this excerpt (emphasis mine):
![create task](../images/async-create-task.jpeg) ![create task](../images/async-create-task.jpeg)
@@ -23,4 +23,4 @@ But who reads all the docs? And who has perfect recall if they do? A search on G
I suspect the reason this mistake is so common is that tasks are a lot like threads (conceptually at least). With threads you can just launch them and forget. Unless you mark them as "daemon" threads they will exist for the lifetime of your app. Not so with Tasks. I suspect the reason this mistake is so common is that tasks are a lot like threads (conceptually at least). With threads you can just launch them and forget. Unless you mark them as "daemon" threads they will exist for the lifetime of your app. Not so with Tasks.
The solution, as recommended in the docs, is to keep a reference to the task for as long as you need it to live. You could also use [TaskGroups](https://docs.python.org/3/library/asyncio-task.html#task-groups) which will keep references to your tasks. As long as all the tasks you spin up are in TaskGroups, you should be fine. The solution recommended in the docs is to keep a reference to the task for as long as you need it to live. On modern Pythons you could also use [TaskGroups](https://docs.python.org/3/library/asyncio-task.html#task-groups) which will keep references to your tasks. As long as all the tasks you spin up are in TaskGroups, you should be fine.