Fix memory streams incorrectly raising cancelled when *_nowait() is called immediately after cancelling send()/receive()
#729
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…) when calling *_nowait() immediately after cancelling send()/receive() * In the send_nowait() + receive() case, this bug could drop items. * In the send() + receive_nowait() case, this bug could cause send() to raise even though it succeeded.
…alled immediately after cancelling send()/receive() This partially reverts commit 6b0a1f3. Co-authored-by: Alex Grönholm <alex.gronholm@nextday.fi>
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This was the first solution that came to my mind, but then I realized it would interact poorly with asyncio's native cancellation. |
could you elaborate on this? i do see now that the branch of |
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send_nowait() immediately after cancelling receive()*_nowait() immediately after cancelling send()/receive()
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(i just updated this branch to also test for and fix the analogous bug that can occur when |
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*_nowait() immediately after cancelling send()/receive()*_nowait() is called immediately after cancelling send()/receive()
| # Ignore the immediate cancellation if we already sent the item, so as | ||
| # to not indicate failure despite success | ||
| if send_event in self._state.waiting_senders: | ||
| del self._state.waiting_senders[send_event] | ||
| raise |
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This would be fine when the cancellation originates from a cancel scope, but not when a task was natively cancelled (Task.cancel(), because the originator of that cancellation expects the cancellation to be acted on and not ignored). Doing this will lead to hangs.
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Closing in favor of #735, as I've come to the conclusion that avoiding the item delivery to a task with a pending cancellation is the only viable solution. |
Changes
Fixes:
MemoryObjectStream can drop items when the receiving end is cancelled #728 (in sense (1) as defined in MemoryObjectStream can drop items when the receiving end is cancelled #728 (comment)). cancellation of
receive()could drop items, meaning that neither the attempted sender nor the attempted receiver think they are responsible for the item.the analogous issue about cancellation of
send(). cancellation ofsend()could result insend()raising cancelled despite succeeding, meaning that both the attempted sender and the attempted receiver think they are responsible for the item.Checklist
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