Description
There are multiple instances of both asyncio.create_task()
and asyncio.create_future()
scattered throughout the library and the examples, where the returned task object is discarded. This is incorrect and can lead to (long-running) tasks disappearing mid-execution. This is explained in the documentation.
Docs for asyncio.create_task()
:
Important: Save a reference to the result of this function, to avoid a task disappearing mid-execution. The event loop only keeps weak references to tasks. A task that isn’t referenced elsewhere may get garbage collected at any time, even before it’s done. For reliable “fire-and-forget” background tasks, gather them in a collection:
background_tasks = set() for i in range(10): task = asyncio.create_task(some_coro(param=i)) # Add task to the set. This creates a strong reference. background_tasks.add(task) # To prevent keeping references to finished tasks forever, # make each task remove its own reference from the set after # completion: task.add_done_callback(background_tasks.discard)
Docs for asyncio.ensure_future()
:
Important See also the create_task() function which is the preferred way for creating new Tasks.
Save a reference to the result of this function, to avoid a task disappearing mid-execution.