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Clarify receive blocking behaviour

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Andrew Godwin 2017-05-25 10:21:07 -07:00
parent 863e298923
commit 7cd4fb2b42
1 changed files with 7 additions and 12 deletions
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docs/asgi.rst
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@ -331,7 +331,8 @@ A *channel layer* must provide an object with these attributes
* ``receive(channels, block=False)``, a callable that takes a list of channel * ``receive(channels, block=False)``, a callable that takes a list of channel
names as unicode strings, and returns with either ``(None, None)`` names as unicode strings, and returns with either ``(None, None)``
or ``(channel, message)`` if a message is available. If ``block`` is True, then or ``(channel, message)`` if a message is available. If ``block`` is True, then
it will not return until after a built-in timeout or a message arrives; if it will not return a message arrives (or optionally, a built-in timeout,
but it is valid to block forever if there are no messages); if
``block`` is false, it will always return immediately. It is perfectly ``block`` is false, it will always return immediately. It is perfectly
valid to ignore ``block`` and always return immediately, or after a delay; valid to ignore ``block`` and always return immediately, or after a delay;
``block`` means that the call can take as long as it likes before returning ``block`` means that the call can take as long as it likes before returning
@ -409,21 +410,15 @@ A channel layer implementing the ``twisted`` extension must also provide:
* ``receive_twisted(channels)``, a function that behaves * ``receive_twisted(channels)``, a function that behaves
like ``receive`` but that returns a Twisted Deferred that eventually like ``receive`` but that returns a Twisted Deferred that eventually
returns either ``(channel, message)`` or ``(None, None)``. It is not possible returns either ``(channel, message)`` or ``(None, None)``. It is not possible
to run it in nonblocking mode; use the normal ``receive`` for that. The to run it in nonblocking mode; use the normal ``receive`` for that.
channel layer must be able to deal with this function being called from
many different places in a codebase simultaneously - likely once from each
Twisted Protocol instance - and so it is recommended that implementations
use internal connection pooling and call merging or similar.
A channel layer implementing the ``asyncio`` extension must also provide: A channel layer implementing the ``async`` extension must also provide:
* ``receive_asyncio(channels)``, a function that behaves * ``receive_async(channels)``, a function that behaves
like ``receive`` but that fulfills the asyncio coroutine contract to like ``receive`` but that fulfills the asyncio coroutine contract to
block until either a result is available or an internal timeout is reached block until either a result is available or an internal timeout is reached
and ``(None, None)`` is returned. The channel layer must be able to deal and ``(None, None)`` is returned. It is not possible
with this function being called from many different places in a codebase to run it in nonblocking mode; use the normal ``receive`` for that.
simultaneously, and so it is recommended that implementations
use internal connection pooling and call merging or similar.
Channel Semantics Channel Semantics
----------------- -----------------