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[3.13] gh-75279: Document that asyncio StreamWriter.drain() may not yield to the event loop (GH-155132) #155136

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kumaraditya303 merged 1 commit into from
Aug 4, 2026
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[3.13] gh-75279: Document that asyncio StreamWriter.drain() may not yield to the event loop (GH-155132) #155136

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10 changes: 10 additions & 0 deletions Doc/library/asyncio-stream.rst
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Expand Up @@ -382,6 +382,16 @@ StreamWriter
be resumed. When there is nothing to wait for, the :meth:`drain`
returns immediately.

.. note::

When the write buffer is below the high watermark,
:meth:`drain` returns immediately without yielding to
the event loop. As a result, code which repeatedly calls
``write()`` followed by ``await drain()`` may prevent other
tasks from running. To prevent blocking behavior, yield
to the event loop explicitly with ``await asyncio.sleep(0)``
(see :func:`asyncio.sleep`).

.. method:: start_tls(sslcontext, *, server_hostname=None, \
ssl_handshake_timeout=None, ssl_shutdown_timeout=None)
:async:
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