calibre-web/vendor/blinker/base.py
2016-04-27 17:47:31 +02:00

427 lines
14 KiB
Python

# -*- coding: utf-8; fill-column: 76 -*-
"""Signals and events.
A small implementation of signals, inspired by a snippet of Django signal
API client code seen in a blog post. Signals are first-class objects and
each manages its own receivers and message emission.
The :func:`signal` function provides singleton behavior for named signals.
"""
from warnings import warn
from weakref import WeakValueDictionary
from blinker._utilities import (
WeakTypes,
contextmanager,
defaultdict,
hashable_identity,
lazy_property,
reference,
symbol,
)
ANY = symbol('ANY')
ANY.__doc__ = 'Token for "any sender".'
ANY_ID = 0
class Signal(object):
"""A notification emitter."""
#: An :obj:`ANY` convenience synonym, allows ``Signal.ANY``
#: without an additional import.
ANY = ANY
@lazy_property
def receiver_connected(self):
"""Emitted after each :meth:`connect`.
The signal sender is the signal instance, and the :meth:`connect`
arguments are passed through: *receiver*, *sender*, and *weak*.
.. versionadded:: 1.2
"""
return Signal(doc="Emitted after a receiver connects.")
@lazy_property
def receiver_disconnected(self):
"""Emitted after :meth:`disconnect`.
The sender is the signal instance, and the :meth:`disconnect` arguments
are passed through: *receiver* and *sender*.
Note, this signal is emitted **only** when :meth:`disconnect` is
called explicitly.
The disconnect signal can not be emitted by an automatic disconnect
(due to a weakly referenced receiver or sender going out of scope),
as the receiver and/or sender instances are no longer available for
use at the time this signal would be emitted.
An alternative approach is available by subscribing to
:attr:`receiver_connected` and setting up a custom weakref cleanup
callback on weak receivers and senders.
.. versionadded:: 1.2
"""
return Signal(doc="Emitted after a receiver disconnects.")
def __init__(self, doc=None):
"""
:param doc: optional. If provided, will be assigned to the signal's
__doc__ attribute.
"""
if doc:
self.__doc__ = doc
#: A mapping of connected receivers.
#:
#: The values of this mapping are not meaningful outside of the
#: internal :class:`Signal` implementation, however the boolean value
#: of the mapping is useful as an extremely efficient check to see if
#: any receivers are connected to the signal.
self.receivers = {}
self._by_receiver = defaultdict(set)
self._by_sender = defaultdict(set)
self._weak_senders = {}
def connect(self, receiver, sender=ANY, weak=True):
"""Connect *receiver* to signal events sent by *sender*.
:param receiver: A callable. Will be invoked by :meth:`send` with
`sender=` as a single positional argument and any \*\*kwargs that
were provided to a call to :meth:`send`.
:param sender: Any object or :obj:`ANY`, defaults to ``ANY``.
Restricts notifications delivered to *receiver* to only those
:meth:`send` emissions sent by *sender*. If ``ANY``, the receiver
will always be notified. A *receiver* may be connected to
multiple *sender* values on the same Signal through multiple calls
to :meth:`connect`.
:param weak: If true, the Signal will hold a weakref to *receiver*
and automatically disconnect when *receiver* goes out of scope or
is garbage collected. Defaults to True.
"""
receiver_id = hashable_identity(receiver)
if weak:
receiver_ref = reference(receiver, self._cleanup_receiver)
receiver_ref.receiver_id = receiver_id
else:
receiver_ref = receiver
if sender is ANY:
sender_id = ANY_ID
else:
sender_id = hashable_identity(sender)
self.receivers.setdefault(receiver_id, receiver_ref)
self._by_sender[sender_id].add(receiver_id)
self._by_receiver[receiver_id].add(sender_id)
del receiver_ref
if sender is not ANY and sender_id not in self._weak_senders:
# wire together a cleanup for weakref-able senders
try:
sender_ref = reference(sender, self._cleanup_sender)
sender_ref.sender_id = sender_id
except TypeError:
pass
else:
self._weak_senders.setdefault(sender_id, sender_ref)
del sender_ref
# broadcast this connection. if receivers raise, disconnect.
if ('receiver_connected' in self.__dict__ and
self.receiver_connected.receivers):
try:
self.receiver_connected.send(self,
receiver=receiver,
sender=sender,
weak=weak)
except:
self.disconnect(receiver, sender)
raise
if receiver_connected.receivers and self is not receiver_connected:
try:
receiver_connected.send(self,
receiver_arg=receiver,
sender_arg=sender,
weak_arg=weak)
except:
self.disconnect(receiver, sender)
raise
return receiver
def connect_via(self, sender, weak=False):
"""Connect the decorated function as a receiver for *sender*.
:param sender: Any object or :obj:`ANY`. The decorated function
will only receive :meth:`send` emissions sent by *sender*. If
``ANY``, the receiver will always be notified. A function may be
decorated multiple times with differing *sender* values.
:param weak: If true, the Signal will hold a weakref to the
decorated function and automatically disconnect when *receiver*
goes out of scope or is garbage collected. Unlike
:meth:`connect`, this defaults to False.
The decorated function will be invoked by :meth:`send` with
`sender=` as a single positional argument and any \*\*kwargs that
were provided to the call to :meth:`send`.
.. versionadded:: 1.1
"""
def decorator(fn):
self.connect(fn, sender, weak)
return fn
return decorator
@contextmanager
def connected_to(self, receiver, sender=ANY):
"""Execute a block with the signal temporarily connected to *receiver*.
:param receiver: a receiver callable
:param sender: optional, a sender to filter on
This is a context manager for use in the ``with`` statement. It can
be useful in unit tests. *receiver* is connected to the signal for
the duration of the ``with`` block, and will be disconnected
automatically when exiting the block:
.. testsetup::
from __future__ import with_statement
from blinker import Signal
on_ready = Signal()
receiver = lambda sender: None
.. testcode::
with on_ready.connected_to(receiver):
# do stuff
on_ready.send(123)
.. versionadded:: 1.1
"""
self.connect(receiver, sender=sender, weak=False)
try:
yield None
except:
self.disconnect(receiver)
raise
else:
self.disconnect(receiver)
def temporarily_connected_to(self, receiver, sender=ANY):
"""An alias for :meth:`connected_to`.
:param receiver: a receiver callable
:param sender: optional, a sender to filter on
.. versionadded:: 0.9
.. versionchanged:: 1.1
Renamed to :meth:`connected_to`. ``temporarily_connected_to``
was deprecated in 1.2 and removed in a subsequent version.
"""
warn("temporarily_connected_to is deprecated; "
"use connected_to instead.",
DeprecationWarning)
return self.connected_to(receiver, sender)
def send(self, *sender, **kwargs):
"""Emit this signal on behalf of *sender*, passing on \*\*kwargs.
Returns a list of 2-tuples, pairing receivers with their return
value. The ordering of receiver notification is undefined.
:param \*sender: Any object or ``None``. If omitted, synonymous
with ``None``. Only accepts one positional argument.
:param \*\*kwargs: Data to be sent to receivers.
"""
# Using '*sender' rather than 'sender=None' allows 'sender' to be
# used as a keyword argument- i.e. it's an invisible name in the
# function signature.
if len(sender) == 0:
sender = None
elif len(sender) > 1:
raise TypeError('send() accepts only one positional argument, '
'%s given' % len(sender))
else:
sender = sender[0]
if not self.receivers:
return []
else:
return [(receiver, receiver(sender, **kwargs))
for receiver in self.receivers_for(sender)]
def has_receivers_for(self, sender):
"""True if there is probably a receiver for *sender*.
Performs an optimistic check only. Does not guarantee that all
weakly referenced receivers are still alive. See
:meth:`receivers_for` for a stronger search.
"""
if not self.receivers:
return False
if self._by_sender[ANY_ID]:
return True
if sender is ANY:
return False
return hashable_identity(sender) in self._by_sender
def receivers_for(self, sender):
"""Iterate all live receivers listening for *sender*."""
# TODO: test receivers_for(ANY)
if self.receivers:
sender_id = hashable_identity(sender)
if sender_id in self._by_sender:
ids = (self._by_sender[ANY_ID] |
self._by_sender[sender_id])
else:
ids = self._by_sender[ANY_ID].copy()
for receiver_id in ids:
receiver = self.receivers.get(receiver_id)
if receiver is None:
continue
if isinstance(receiver, WeakTypes):
strong = receiver()
if strong is None:
self._disconnect(receiver_id, ANY_ID)
continue
receiver = strong
yield receiver
def disconnect(self, receiver, sender=ANY):
"""Disconnect *receiver* from this signal's events.
:param receiver: a previously :meth:`connected<connect>` callable
:param sender: a specific sender to disconnect from, or :obj:`ANY`
to disconnect from all senders. Defaults to ``ANY``.
"""
if sender is ANY:
sender_id = ANY_ID
else:
sender_id = hashable_identity(sender)
receiver_id = hashable_identity(receiver)
self._disconnect(receiver_id, sender_id)
if ('receiver_disconnected' in self.__dict__ and
self.receiver_disconnected.receivers):
self.receiver_disconnected.send(self,
receiver=receiver,
sender=sender)
def _disconnect(self, receiver_id, sender_id):
if sender_id == ANY_ID:
if self._by_receiver.pop(receiver_id, False):
for bucket in self._by_sender.values():
bucket.discard(receiver_id)
self.receivers.pop(receiver_id, None)
else:
self._by_sender[sender_id].discard(receiver_id)
def _cleanup_receiver(self, receiver_ref):
"""Disconnect a receiver from all senders."""
self._disconnect(receiver_ref.receiver_id, ANY_ID)
def _cleanup_sender(self, sender_ref):
"""Disconnect all receivers from a sender."""
sender_id = sender_ref.sender_id
assert sender_id != ANY_ID
self._weak_senders.pop(sender_id, None)
for receiver_id in self._by_sender.pop(sender_id, ()):
self._by_receiver[receiver_id].discard(sender_id)
def _clear_state(self):
"""Throw away all signal state. Useful for unit tests."""
self._weak_senders.clear()
self.receivers.clear()
self._by_sender.clear()
self._by_receiver.clear()
receiver_connected = Signal("""\
Sent by a :class:`Signal` after a receiver connects.
:argument: the Signal that was connected to
:keyword receiver_arg: the connected receiver
:keyword sender_arg: the sender to connect to
:keyword weak_arg: true if the connection to receiver_arg is a weak reference
.. deprecated:: 1.2
As of 1.2, individual signals have their own private
:attr:`~Signal.receiver_connected` and
:attr:`~Signal.receiver_disconnected` signals with a slightly simplified
call signature. This global signal is planned to be removed in 1.6.
""")
class NamedSignal(Signal):
"""A named generic notification emitter."""
def __init__(self, name, doc=None):
Signal.__init__(self, doc)
#: The name of this signal.
self.name = name
def __repr__(self):
base = Signal.__repr__(self)
return "%s; %r>" % (base[:-1], self.name)
class Namespace(dict):
"""A mapping of signal names to signals."""
def signal(self, name, doc=None):
"""Return the :class:`NamedSignal` *name*, creating it if required.
Repeated calls to this function will return the same signal object.
"""
try:
return self[name]
except KeyError:
return self.setdefault(name, NamedSignal(name, doc))
class WeakNamespace(WeakValueDictionary):
"""A weak mapping of signal names to signals.
Automatically cleans up unused Signals when the last reference goes out
of scope. This namespace implementation exists for a measure of legacy
compatibility with Blinker <= 1.2, and may be dropped in the future.
"""
def signal(self, name, doc=None):
"""Return the :class:`NamedSignal` *name*, creating it if required.
Repeated calls to this function will return the same signal object.
"""
try:
return self[name]
except KeyError:
return self.setdefault(name, NamedSignal(name, doc))
signal = Namespace().signal