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Diffstat (limited to 'Doc/library/asyncio-task.rst')
| -rw-r--r-- | Doc/library/asyncio-task.rst | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst index 3b10a0d628a..3d300c37419 100644 --- a/Doc/library/asyncio-task.rst +++ b/Doc/library/asyncio-task.rst @@ -392,6 +392,27 @@ is also included in the exception group. The same special case is made for :exc:`KeyboardInterrupt` and :exc:`SystemExit` as in the previous paragraph. +Task groups are careful not to mix up the internal cancellation used to +"wake up" their :meth:`~object.__aexit__` with cancellation requests +for the task in which they are running made by other parties. +In particular, when one task group is syntactically nested in another, +and both experience an exception in one of their child tasks simultaneously, +the inner task group will process its exceptions, and then the outer task group +will receive another cancellation and process its own exceptions. + +In the case where a task group is cancelled externally and also must +raise an :exc:`ExceptionGroup`, it will call the parent task's +:meth:`~asyncio.Task.cancel` method. This ensures that a +:exc:`asyncio.CancelledError` will be raised at the next +:keyword:`await`, so the cancellation is not lost. + +Task groups preserve the cancellation count +reported by :meth:`asyncio.Task.cancelling`. + +.. versionchanged:: 3.13 + + Improved handling of simultaneous internal and external cancellations + and correct preservation of cancellation counts. Sleeping ======== @@ -1369,6 +1390,15 @@ Task Object catching :exc:`CancelledError`, it needs to call this method to remove the cancellation state. + When this method decrements the cancellation count to zero, + the method checks if a previous :meth:`cancel` call had arranged + for :exc:`CancelledError` to be thrown into the task. + If it hasn't been thrown yet, that arrangement will be + rescinded (by resetting the internal ``_must_cancel`` flag). + + .. versionchanged:: 3.13 + Changed to rescind pending cancellation requests upon reaching zero. + .. method:: cancelling() Return the number of pending cancellation requests to this Task, i.e., |