from __future__ import annotations
import collections.abc as c
import sys
import typing as t
import weakref
from collections import defaultdict
from contextlib import contextmanager
from functools import cached_property
from inspect import iscoroutinefunction
from ._utilities import make_id
from ._utilities import make_ref
from ._utilities import Symbol
F = t.TypeVar("F", bound=c.Callable[..., t.Any])
ANY = Symbol("ANY")
"""Symbol for "any sender"."""
ANY_ID = 0
class Signal:
"""A notification emitter.
:param doc: The docstring for the signal.
"""
ANY = ANY
"""An alias for the :data:`~blinker.ANY` sender symbol."""
set_class: type[set[t.Any]] = set
"""The set class to use for tracking connected receivers and senders.
Python's ``set`` is unordered. If receivers must be dispatched in the order
they were connected, an ordered set implementation can be used.
.. versionadded:: 1.7
"""
@cached_property
def receiver_connected(self) -> Signal:
"""Emitted at the end of each :meth:`connect` call.
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.")
@cached_property
def receiver_disconnected(self) -> Signal:
"""Emitted at the end of each :meth:`disconnect` call.
The sender is the signal instance, and the :meth:`disconnect` arguments
are passed through: ``receiver`` and ``sender``.
This signal is emitted **only** when :meth:`disconnect` is called
explicitly. This signal cannot be emitted by an automatic disconnect
when a weakly referenced receiver or sender goes out of scope, as the
instance is no longer be available to be used as the sender for this
signal.
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: str | None = None) -> None:
if doc:
self.__doc__ = doc
self.receivers: dict[
t.Any, weakref.ref[c.Callable[..., t.Any]] | c.Callable[..., t.Any]
] = {}
"""The map of connected receivers. Useful to quickly check if any
receivers are connected to the signal: ``if s.receivers:``. The
structure and data is not part of the public API, but checking its
boolean value is.
"""
self.is_muted: bool = False
self._by_receiver: dict[t.Any, set[t.Any]] = defaultdict(self.set_class)
self._by_sender: dict[t.Any, set[t.Any]] = defaultdict(self.set_class)
self._weak_senders: dict[t.Any, weakref.ref[t.Any]] = {}
def connect(self, receiver: F, sender: t.Any = ANY, weak: bool = True) -> F:
"""Connect ``receiver`` to be called when the signal is sent by
``sender``.
:param receiver: The callable to call when :meth:`send` is called with
the given ``sender``, passing ``sender`` as a positional argument
along with any extra keyword arguments.
:param sender: Any object or :data:`ANY`. ``receiver`` will only be
called when :meth:`send` is called with this sender. If ``ANY``, the
receiver will be called for any sender. A receiver may be connected
to multiple senders by calling :meth:`connect` multiple times.
:param weak: Track the receiver with a :mod:`weakref`. The receiver will
be automatically disconnected when it is garbage collected. When
connecting a receiver defined within a function, set to ``False``,
otherwise it will be disconnected when the function scope ends.
"""
receiver_id = make_id(receiver)
sender_id = ANY_ID if sender is ANY else make_id(sender)
if weak:
self.receivers[receiver_id] = make_ref(
receiver, self._make_cleanup_receiver(receiver_id)
)
else:
self.receivers[receiver_id] = receiver
self._by_sender[sender_id].add(receiver_id)
self._by_receiver[receiver_id].add(sender_id)
if sender is not ANY and sender_id not in self._weak_senders:
# store a cleanup for weakref-able senders
try:
self._weak_senders[sender_id] = make_ref(
sender, self._make_cleanup_sender(sender_id)
)
except TypeError:
pass
if "receiver_connected" in self.__dict__ and self.receiver_connected.receivers:
try:
self.receiver_connected.send(
self, receiver=receiver, sender=sender, weak=weak
)
except TypeError:
# TODO no explanation or test for this
self.disconnect(receiver, sender)
raise
return receiver
def connect_via(self, sender: t.Any, weak: bool = False) -> c.Callable[[F], F]:
"""Connect the decorated function to be called when the signal is sent
by ``sender``.
The decorated function will be called when :meth:`send` is called with
the given ``sender``, passing ``sender`` as a positional argument along
with any extra keyword arguments.
:param sender: Any object or :data:`ANY`. ``receiver`` will only be
called when :meth:`send` is called with this sender. If ``ANY``, the
receiver will be called for any sender. A receiver may be connected
to multiple senders by calling :meth:`connect` multiple times.
:param weak: Track the receiver with a :mod:`weakref`. The receiver will
be automatically disconnected when it is garbage collected. When
connecting a receiver defined within a function, set to ``False``,
otherwise it will be disconnected when the function scope ends.=
.. versionadded:: 1.1
"""
def decorator(fn: F) -> F:
self.connect(fn, sender, weak)
return fn
return decorator
@contextmanager
def connected_to(
self, receiver: c.Callable[..., t.Any], sender: t.Any = ANY
) -> c.Generator[None, None, None]:
"""A context manager that temporarily connects ``receiver`` to the
signal while a ``with`` block executes. When the block exits, the
receiver is disconnected. Useful for tests.
:param receiver: The callable to call when :meth:`send` is called with
the given ``sender``, passing ``sender`` as a positional argument
along with any extra keyword arguments.
:param sender: Any object or :data:`ANY`. ``receiver`` will only be
called when :meth:`send` is called with this sender. If ``ANY``, the
receiver will be called for any sender.
.. versionadded:: 1.1
"""
self.connect(receiver, sender=sender, weak=False)
try:
yield None
finally:
self.disconnect(receiver)
@contextmanager
def muted(self) -> c.Generator[None, None, None]:
"""A context manager that temporarily disables the signal. No receivers
will be called if the signal is sent, until the ``with`` block exits.
Useful for tests.
"""
self.is_muted = True
try:
yield None
finally:
self.is_muted = False
def send(
self,
sender: t.Any | None = None,
/,
*,
_async_wrapper: c.Callable[
[c.Callable[..., c.Coroutine[t.Any, t.Any, t.Any]]], c.Callable[..., t.Any]
]
| None = None,
**kwargs: t.Any,
) -> list[tuple[c.Callable[..., t.Any], t.Any]]:
"""Call all receivers that are connected to the given ``sender``
or :data:`ANY`. Each receiver is called with ``sender`` as a positional
argument along with any extra keyword arguments. Return a list of
``(receiver, return value)`` tuples.
The order receivers are called is undefined, but can be influenced by
setting :attr:`set_class`.
If a receiver raises an exception, that exception will propagate up.
This makes debugging straightforward, with an assumption that correctly
implemented receivers will not raise.
:param sender: Call receivers connected to this sender, in addition to
those connected to :data:`ANY`.
:param _async_wrapper: Will be called on any receivers that are async
coroutines to turn them into sync callables. For example, could run
the receiver with an event loop.
:param kwargs: Extra keyword arguments to pass to each receiver.
.. versionchanged:: 1.7
Added the ``_async_wrapper`` argument.
"""
if self.is_muted:
return []
results = []
for receiver in self.receivers_for(sender):
if iscoroutinefunction(receiver):
if _async_wrapper is None:
raise RuntimeError("Cannot send to a coroutine function.")
result = _async_wrapper(receiver)(sender, **kwargs)
else:
result = receiver(sender, **kwargs)
results.append((receiver, result))
return results
async def send_async(
self,
sender: t.Any | None = None,
/,
*,
_sync_wrapper: c.Callable[
[c.Callable[..., t.Any]], c.Callable[..., c.Coroutine[t.Any, t.Any, t.Any]]
]
| None = None,
**kwargs: t.Any,
) -> list[tuple[c.Callable[..., t.Any], t.Any]]:
"""Await all receivers that are connected to the given ``sender``
or :data:`ANY`. Each receiver is called with ``sender`` as a positional
argument along with any extra keyword arguments. Return a list of
``(receiver, return value)`` tuples.
The order receivers are called is undefined, but can be influenced by
setting :attr:`set_class`.
If a receiver raises an exception, that exception will propagate up.
This makes debugging straightforward, with an assumption that correctly
implemented receivers will not raise.
:param sender: Call receivers connected to this sender, in addition to
those connected to :data:`ANY`.
:param _sync_wrapper: Will be called on any receivers that are sync
callables to turn them into async coroutines. For example,
could call the receiver in a thread.
:param kwargs: Extra keyword arguments to pass to each receiver.
.. versionadded:: 1.7
"""
if self.is_muted:
return []
results = []
for receiver in self.receivers_for(sender):
if not iscoroutinefunction(receiver):
if _sync_wrapper is None:
raise RuntimeError("Cannot send to a non-coroutine function.")
result = await _sync_wrapper(receiver)(sender, **kwargs)
else:
result = await receiver(sender, **kwargs)
results.append((receiver, result))
return results
def has_receivers_for(self, sender: t.Any) -> bool:
"""Check if there is at least one receiver that will be called with the
given ``sender``. A receiver connected to :data:`ANY` will always be
called, regardless of sender. Does not check if weakly referenced
receivers are still live. See :meth:`receivers_for` for a stronger
search.
:param sender: Check for receivers connected to this sender, in addition
to those connected to :data:`ANY`.
"""
if not self.receivers:
return False
if self._by_sender[ANY_ID]:
return True
if sender is ANY:
return False
return make_id(sender) in self._by_sender
def receivers_for(
self, sender: t.Any
) -> c.Generator[c.Callable[..., t.Any], None, None]:
"""Yield each receiver to be called for ``sender``, in addition to those
to be called for :data:`ANY`. Weakly referenced receivers that are not
live will be disconnected and skipped.
:param sender: Yield receivers connected to this sender, in addition
to those connected to :data:`ANY`.
"""
# TODO: test receivers_for(ANY)
if not self.receivers:
return
sender_id = make_id(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, weakref.ref):
strong = receiver()
if strong is None:
self._disconnect(receiver_id, ANY_ID)
continue
yield strong
else:
yield receiver
def disconnect(self, receiver: c.Callable[..., t.Any], sender: t.Any = ANY) -> None:
"""Disconnect ``receiver`` from being called when the signal is sent by
``sender``.
:param receiver: A connected receiver callable.
:param sender: Disconnect from only this sender. By default, disconnect
from all senders.
"""
sender_id: c.Hashable
if sender is ANY:
sender_id = ANY_ID
else:
sender_id = make_id(sender)
receiver_id = make_id(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: c.Hashable, sender_id: c.Hashable) -> None:
if sender_id == ANY_ID:
if self._by_receiver.pop(receiver_id, None) is not None:
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)
self._by_receiver[receiver_id].discard(sender_id)
def _make_cleanup_receiver(
self, receiver_id: c.Hashable
) -> c.Callable[[weakref.ref[c.Callable[..., t.Any]]], None]:
"""Create a callback function to disconnect a weakly referenced
receiver when it is garbage collected.
"""
def cleanup(ref: weakref.ref[c.Callable[..., t.Any]]) -> None:
# If the interpreter is shutting down, disconnecting can result in a
# weird ignored exception. Don't call it in that case.
if not sys.is_finalizing():
self._disconnect(receiver_id, ANY_ID)
return cleanup
def _make_cleanup_sender(
self, sender_id: c.Hashable
) -> c.Callable[[weakref.ref[t.Any]], None]:
"""Create a callback function to disconnect all receivers for a weakly
referenced sender when it is garbage collected.
"""
assert sender_id != ANY_ID
def cleanup(ref: weakref.ref[t.Any]) -> None:
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)
return cleanup
def _cleanup_bookkeeping(self) -> None:
"""Prune unused sender/receiver bookkeeping. Not threadsafe.
Connecting & disconnecting leaves behind a small amount of bookkeeping
data. Typical workloads using Blinker, for example in most web apps,
Flask, CLI scripts, etc., are not adversely affected by this
bookkeeping.
With a long-running process performing dynamic signal routing with high
volume, e.g. connecting to function closures, senders are all unique
object instances. Doing all of this over and over may cause memory usage
to grow due to extraneous bookkeeping. (An empty ``set`` for each stale
sender/receiver pair.)
This method will prune that bookkeeping away, with the caveat that such
pruning is not threadsafe. The risk is that cleanup of a fully
disconnected receiver/sender pair occurs while another thread is
connecting that same pair. If you are in the highly dynamic, unique
receiver/sender situation that has lead you to this method, that failure
mode is perhaps not a big deal for you.
"""
for mapping in (self._by_sender, self._by_receiver):
for ident, bucket in list(mapping.items()):
if not bucket:
mapping.pop(ident, None)
def _clear_state(self) -> None:
"""Disconnect all receivers and senders. Useful for tests."""
self._weak_senders.clear()
self.receivers.clear()
self._by_sender.clear()
self._by_receiver.clear()
class NamedSignal(Signal):
"""A named generic notification emitter. The name is not used by the signal
itself, but matches the key in the :class:`Namespace` that it belongs to.
:param name: The name of the signal within the namespace.
:param doc: The docstring for the signal.
"""
def __init__(self, name: str, doc: str | None = None) -> None:
super().__init__(doc)
#: The name of this signal.
self.name: str = name
def __repr__(self) -> str:
base = super().__repr__()
return f"{base[:-1]}; {self.name!r}>" # noqa: E702
class Namespace(dict[str, NamedSignal]):
"""A dict mapping names to signals."""
def signal(self, name: str, doc: str | None = None) -> NamedSignal:
"""Return the :class:`NamedSignal` for the given ``name``, creating it
if required. Repeated calls with the same name return the same signal.
:param name: The name of the signal.
:param doc: The docstring of the signal.
"""
if name not in self:
self[name] = NamedSignal(name, doc)
return self[name]
class _PNamespaceSignal(t.Protocol):
def __call__(self, name: str, doc: str | None = None) -> NamedSignal: ...
default_namespace: Namespace = Namespace()
"""A default :class:`Namespace` for creating named signals. :func:`signal`
creates a :class:`NamedSignal` in this namespace.
"""
signal: _PNamespaceSignal = default_namespace.signal
"""Return a :class:`NamedSignal` in :data:`default_namespace` with the given
``name``, creating it if required. Repeated calls with the same name return the
same signal.
"""