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Signals
=======
.. currentmodule:: aiohttp
Signal is a list of registered asynchronous callbacks.
The signal's life-cycle has two stages: after creation its content
could be filled by using standard list operations: ``sig.append()``
etc.
After ``sig.freeze()`` call the signal is *frozen*: adding, removing
and dropping callbacks are forbidden.
The only available operation is calling previously registered
callbacks by ``await sig.send(data)``.
For concrete usage examples see :ref:`signals in aiohttp.web
<aiohttp-web-signals>` chapter.
.. versionchanged:: 3.0
``sig.send()`` call is forbidden for non-frozen signal.
Support for regular (non-async) callbacks is dropped. All callbacks
should be async functions.
.. class:: Signal
The signal, implements :class:`collections.abc.MutableSequence`
interface.
.. comethod:: send(*args, **kwargs)
Call all registered callbacks one by one starting from the begin
of list.
.. attribute:: frozen
``True`` if :meth:`freeze` was called, read-only property.
.. method:: freeze()
Freeze the list. After the call any content modification is forbidden.
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