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-rw-r--r--Doc/library/asyncio-protocol.rst13
1 files changed, 11 insertions, 2 deletions
diff --git a/Doc/library/asyncio-protocol.rst b/Doc/library/asyncio-protocol.rst
index dabe7d8..cbbc151 100644
--- a/Doc/library/asyncio-protocol.rst
+++ b/Doc/library/asyncio-protocol.rst
@@ -376,8 +376,8 @@ The following callbacks are called on :class:`DatagramProtocol` instances.
Flow control callbacks
----------------------
-These callbacks may be called on :class:`Protocol` and
-:class:`SubprocessProtocol` instances:
+These callbacks may be called on :class:`Protocol`,
+:class:`DatagramProtocol` and :class:`SubprocessProtocol` instances:
.. method:: BaseProtocol.pause_writing()
@@ -402,6 +402,15 @@ buffer size reaches the low-water mark.
are important to ensure that things go as expected when either
mark is zero.
+.. note::
+ On BSD systems (OS X, FreeBSD, etc.) flow control is not supported
+ for :class:`DatagramProtocol`, because send failures caused by
+ writing too many packets cannot be detected easily. The socket
+ always appears 'ready' and excess packets are dropped; an
+ :class:`OSError` with errno set to :const:`errno.ENOBUFS` may or
+ may not be raised; if it is raised, it will be reported to
+ :meth:`DatagramProtocol.error_received` but otherwise ignored.
+
Coroutines and protocols
------------------------