Currently, asyncio.wait_for(fut), upon reaching the timeout deadline,
cancels the future and returns immediately. This is problematic for
when *fut* is a Task, because it will be left running for an arbitrary
amount of time. This behavior is iself surprising and may lead to
related bugs such as the one described in bpo-33638:
condition = asyncio.Condition()
async with condition:
await asyncio.wait_for(condition.wait(), timeout=0.5)
Currently, instead of raising a TimeoutError, the above code will fail
with `RuntimeError: cannot wait on un-acquired lock`, because
`__aexit__` is reached _before_ `condition.wait()` finishes its
cancellation and re-acquires the condition lock.
To resolve this, make `wait_for` await for the task cancellation.
The tradeoff here is that the `timeout` promise may be broken if the
task decides to handle its cancellation in a slow way. This represents
a behavior change and should probably not be back-patched to 3.6 and
earlier.
(cherry picked from commit e2b340ab41)
Co-authored-by: Elvis Pranskevichus <elvis@magic.io>
* Convert asyncio/tasks.py to async/await
* Convert asyncio/queues.py to async/await
* Convert asyncio/test_utils.py to async/await
* Convert asyncio/base_subprocess.py to async/await
* Convert asyncio/subprocess.py to async/await
* Convert asyncio/streams.py to async/await
* Fix comments
* Convert asyncio/locks.py to async/await
* Convert asyncio.sleep to async def
* Add a comment
* Add missing news
* Convert stubs from AbstrctEventLoop to async functions
* Convert subprocess_shell/subprocess_exec
* Convert connect_read_pipe/connect_write_pip to async/await syntax
* Convert create_datagram_endpoint
* Convert create_unix_server/create_unix_connection
* Get rid of old style coroutines in unix_events.py
* Convert selector_events.py to async/await
* Convert wait_closed and create_connection
* Drop redundant line
* Convert base_events.py
* Code cleanup
* Drop redundant comments
* Fix indentation
* Add explicit tests for compatibility between old and new coroutines
* Convert windows event loop to use async/await
* Fix double awaiting of async function
* Convert asyncio/locks.py
* Improve docstring
* Convert tests to async/await
* Convert more tests
* Convert more tests
* Convert more tests
* Convert tests
* Improve test
* _WaitHandleFuture.cancel() now notify IocpProactor through the overlapped
object that the wait was cancelled.
* Optimize IocpProactor.wait_for_handle() gets the result if the wait is
signaled immediatly.
* Enhance representation of Future and Future subclasses
- Add "created at filename:lineno" in the representation
- Add Future._repr_info() method which can be more easily overriden than
Future.__repr__(). It should now be more easy to enhance Future
representation without having to modify each subclass. For example,
_OverlappedFuture and _WaitHandleFuture get the new "created at" information.
- Use reprlib to format Future result, and function arguments when formatting a
callback, to limit the length of the representation.
* Fix repr(_WaitHandleFuture)
* _WaitHandleFuture and _OverlappedFuture: hide frames of internal calls in the
source traceback.
* Cleanup ProactorIocp._poll(): set the timeout to 0 after the first call to
GetQueuedCompletionStatus()
* test_locks: close the temporary event loop and check the condition lock
* Remove workaround in test_futures, no more needed
Major changes:
- StreamReader.readexactly() now raises an IncompleteReadError if the
end of stream is reached before we received enough bytes, instead of
returning less bytes than requested.
- Unit tests use the main asyncio module instead of submodules like events
- _UnixWritePipeTransport now also supports character devices, as
_UnixReadPipeTransport. Patch written by Jonathan Slenders.
- Export more symbols: BaseEventLoop, BaseProactorEventLoop,
BaseSelectorEventLoop, Queue and Queue sublasses, Empty, Full
Miss Islington (bot)
Yury Selivanov
Andrew Svetlov
Mathieu Sornay
Martin Panter
Guido van Rossum
Victor Stinner
Guido van Rossum