"""Multiple-producer-multiple-consumer signal-dispatching
dispatcher is the core of the PyDispatcher system,
providing the primary API and the core logic for the
system.
Module attributes of note:
Any -- Singleton used to signal either "Any Sender" or
"Any Signal". See documentation of the _Any class.
Anonymous -- Singleton used to signal "Anonymous Sender"
See documentation of the _Anonymous class.
Internal attributes:
WEAKREF_TYPES -- tuple of types/classes which represent
weak references to receivers, and thus must be de-
referenced on retrieval to retrieve the callable
object
connections -- { senderkey (id) : { signal : [receivers...]}}
senders -- { senderkey (id) : weakref(sender) }
used for cleaning up sender references on sender
deletion
sendersBack -- { receiverkey (id) : [senderkey (id)...] }
used for cleaning up receiver references on receiver
deletion, (considerably speeds up the cleanup process
vs. the original code.)
"""
from __future__ import generators
import weakref
from grass.pydispatch import saferef, robustapply, errors
__author__ = "Patrick K. O'Brien <pobrien@orbtech.com>"
__cvsid__ = "Id: dispatcher.py,v 1.1 2010/03/30 15:45:55 mcfletch Exp"
__version__ = "Revision: 1.1"
class _Parameter:
"""Used to represent default parameter values."""
def __repr__(self):
return self.__class__.__name__
class _Any(_Parameter):
"""Singleton used to signal either "Any Sender" or "Any Signal"
The Any object can be used with connect, disconnect,
send, or sendExact to signal that the parameter given
Any should react to all senders/signals, not just
a particular sender/signal.
"""
Any = _Any()
class _Anonymous(_Parameter):
"""Singleton used to signal "Anonymous Sender"
The Anonymous object is used to signal that the sender
of a message is not specified (as distinct from being
"any sender"). Registering callbacks for Anonymous
will only receive messages sent without senders. Sending
with anonymous will only send messages to those receivers
registered for Any or Anonymous.
Note:
The default sender for connect is Any, while the
default sender for send is Anonymous. This has
the effect that if you do not specify any senders
in either function then all messages are routed
as though there was a single sender (Anonymous)
being used everywhere.
"""
Anonymous = _Anonymous()
WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)
connections = {}
senders = {}
sendersBack = {}
[docs]def connect(receiver, signal=Any, sender=Any, weak=True):
"""Connect receiver to sender for signal
receiver -- a callable Python object which is to receive
messages/signals/events. Receivers must be hashable
objects.
if weak is True, then receiver must be weak-referencable
(more precisely saferef.safeRef() must be able to create
a reference to the receiver).
Receivers are fairly flexible in their specification,
as the machinery in the robustApply module takes care
of most of the details regarding figuring out appropriate
subsets of the sent arguments to apply to a given
receiver.
Note:
if receiver is itself a weak reference (a callable),
it will be de-referenced by the system's machinery,
so *generally* weak references are not suitable as
receivers, though some use might be found for the
facility whereby a higher-level library passes in
pre-weakrefed receiver references.
signal -- the signal to which the receiver should respond
if Any, receiver will receive any signal from the
indicated sender (which might also be Any, but is not
necessarily Any).
Otherwise must be a hashable Python object other than
None (DispatcherError raised on None).
sender -- the sender to which the receiver should respond
if Any, receiver will receive the indicated signals
from any sender.
if Anonymous, receiver will only receive indicated
signals from send/sendExact which do not specify a
sender, or specify Anonymous explicitly as the sender.
Otherwise can be any python object.
weak -- whether to use weak references to the receiver
By default, the module will attempt to use weak
references to the receiver objects. If this parameter
is false, then strong references will be used.
returns None, may raise DispatcherTypeError
"""
if signal is None:
raise errors.DispatcherTypeError(
"Signal cannot be None (receiver=%r sender=%r)" % (receiver, sender)
)
if weak:
receiver = saferef.safeRef(receiver, onDelete=_removeReceiver)
senderkey = id(sender)
if senderkey in connections:
signals = connections[senderkey]
else:
connections[senderkey] = signals = {}
# Keep track of senders for cleanup.
# Is Anonymous something we want to clean up?
if sender not in (None, Anonymous, Any):
def remove(object, senderkey=senderkey):
_removeSender(senderkey=senderkey)
# Skip objects that can not be weakly referenced, which means
# they won't be automatically cleaned up, but that's too bad.
try:
weakSender = weakref.ref(sender, remove)
senders[senderkey] = weakSender
except Exception:
pass
receiverID = id(receiver)
# get current set, remove any current references to
# this receiver in the set, including back-references
if signal in signals:
receivers = signals[signal]
_removeOldBackRefs(senderkey, signal, receiver, receivers)
else:
receivers = signals[signal] = []
try:
current = sendersBack.get(receiverID)
if current is None:
sendersBack[receiverID] = current = []
if senderkey not in current:
current.append(senderkey)
except Exception:
pass
receivers.append(receiver)
[docs]def disconnect(receiver, signal=Any, sender=Any, weak=True):
"""Disconnect receiver from sender for signal
receiver -- the registered receiver to disconnect
signal -- the registered signal to disconnect
sender -- the registered sender to disconnect
weak -- the weakref state to disconnect
disconnect reverses the process of connect,
the semantics for the individual elements are
logically equivalent to a tuple of
(receiver, signal, sender, weak) used as a key
to be deleted from the internal routing tables.
(The actual process is slightly more complex
but the semantics are basically the same).
Note:
Using disconnect is not required to cleanup
routing when an object is deleted, the framework
will remove routes for deleted objects
automatically. It's only necessary to disconnect
if you want to stop routing to a live object.
returns None, may raise DispatcherTypeError or
DispatcherKeyError
"""
if signal is None:
raise errors.DispatcherTypeError(
"Signal cannot be None (receiver=%r sender=%r)" % (receiver, sender)
)
if weak:
receiver = saferef.safeRef(receiver)
senderkey = id(sender)
try:
signals = connections[senderkey]
receivers = signals[signal]
except KeyError:
raise errors.DispatcherKeyError(
"""No receivers found for signal %r from sender %r""" % (signal, sender)
)
try:
# also removes from receivers
_removeOldBackRefs(senderkey, signal, receiver, receivers)
except ValueError:
raise errors.DispatcherKeyError(
"""No connection to receiver %s for signal %s from sender %s"""
% (receiver, signal, sender)
)
_cleanupConnections(senderkey, signal)
[docs]def getReceivers(sender=Any, signal=Any):
"""Get list of receivers from global tables
This utility function allows you to retrieve the
raw list of receivers from the connections table
for the given sender and signal pair.
Note:
there is no guarantee that this is the actual list
stored in the connections table, so the value
should be treated as a simple iterable/truth value
rather than, for instance a list to which you
might append new records.
Normally you would use liveReceivers(getReceivers(...))
to retrieve the actual receiver objects as an iterable
object.
"""
try:
return connections[id(sender)][signal]
except KeyError:
return []
[docs]def liveReceivers(receivers):
"""Filter sequence of receivers to get resolved, live receivers
This is a generator which will iterate over
the passed sequence, checking for weak references
and resolving them, then returning all live
receivers.
"""
for receiver in receivers:
if isinstance(receiver, WEAKREF_TYPES):
# Dereference the weak reference.
receiver = receiver()
if receiver is not None:
yield receiver
else:
yield receiver
[docs]def getAllReceivers(sender=Any, signal=Any):
"""Get list of all receivers from global tables
This gets all receivers which should receive
the given signal from sender, each receiver should
be produced only once by the resulting generator
"""
receivers = {}
for set in (
# Get receivers that receive *this* signal from *this* sender.
getReceivers(sender, signal),
# Add receivers that receive *any* signal from *this* sender.
getReceivers(sender, Any),
# Add receivers that receive *this* signal from *any* sender.
getReceivers(Any, signal),
# Add receivers that receive *any* signal from *any* sender.
getReceivers(Any, Any),
):
for receiver in set:
if receiver: # filter out dead instance-method weakrefs
try:
if receiver not in receivers:
receivers[receiver] = 1
yield receiver
except TypeError:
# dead weakrefs raise TypeError on hash...
pass
[docs]def send(signal=Any, sender=Anonymous, *arguments, **named):
"""Send signal from sender to all connected receivers.
signal -- (hashable) signal value, see connect for details
sender -- the sender of the signal
if Any, only receivers registered for Any will receive
the message.
if Anonymous, only receivers registered to receive
messages from Anonymous or Any will receive the message
Otherwise can be any python object (normally one
registered with a connect if you actually want
something to occur).
arguments -- positional arguments which will be passed to
*all* receivers. Note that this may raise TypeErrors
if the receivers do not allow the particular arguments.
Note also that arguments are applied before named
arguments, so they should be used with care.
named -- named arguments which will be filtered according
to the parameters of the receivers to only provide those
acceptable to the receiver.
Return a list of tuple pairs [(receiver, response), ... ]
if any receiver raises an error, the error propagates back
through send, terminating the dispatch loop, so it is quite
possible to not have all receivers called if a raises an
error.
"""
# Call each receiver with whatever arguments it can accept.
# Return a list of tuple pairs [(receiver, response), ... ].
responses = []
for receiver in liveReceivers(getAllReceivers(sender, signal)):
response = robustapply.robustApply(
receiver, signal=signal, sender=sender, *arguments, **named
)
responses.append((receiver, response))
return responses
[docs]def sendExact(signal=Any, sender=Anonymous, *arguments, **named):
"""Send signal only to those receivers registered for exact message
sendExact allows for avoiding Any/Anonymous registered
handlers, sending only to those receivers explicitly
registered for a particular signal on a particular
sender.
"""
responses = []
for receiver in liveReceivers(getReceivers(sender, signal)):
response = robustapply.robustApply(
receiver, signal=signal, sender=sender, *arguments, **named
)
responses.append((receiver, response))
return responses
def _removeReceiver(receiver):
"""Remove receiver from connections."""
if not sendersBack or not connections:
# During module cleanup the objects will be replaced with None
# The order of replacing many change, so both variables need
# to be checked.
return False
backKey = id(receiver)
try:
backSet = sendersBack.pop(backKey)
except KeyError:
return False
else:
for senderkey in backSet:
try:
signals = list(connections[senderkey])
except KeyError:
pass
else:
for signal in signals:
try:
receivers = connections[senderkey][signal]
except KeyError:
pass
else:
try:
receivers.remove(receiver)
except Exception:
pass
_cleanupConnections(senderkey, signal)
def _cleanupConnections(senderkey, signal):
"""Delete any empty signals for senderkey. Delete senderkey if empty."""
try:
receivers = connections[senderkey][signal]
except Exception:
pass
else:
if not receivers:
# No more connected receivers. Therefore, remove the signal.
try:
signals = connections[senderkey]
except KeyError:
pass
else:
del signals[signal]
if not signals:
# No more signal connections. Therefore, remove the sender.
_removeSender(senderkey)
def _removeSender(senderkey):
"""Remove senderkey from connections."""
_removeBackrefs(senderkey)
try:
del connections[senderkey]
except KeyError:
pass
# Senderkey will only be in senders dictionary if sender
# could be weakly referenced.
try:
del senders[senderkey]
except Exception:
pass
def _removeBackrefs(senderkey):
"""Remove all back-references to this senderkey"""
try:
signals = connections[senderkey]
except KeyError:
signals = None
else:
items = signals.items()
def allReceivers():
for signal, set in items:
for item in set:
yield item
for receiver in allReceivers():
_killBackref(receiver, senderkey)
def _removeOldBackRefs(senderkey, signal, receiver, receivers):
"""Kill old sendersBack references from receiver
This guards against multiple registration of the same
receiver for a given signal and sender leaking memory
as old back reference records build up.
Also removes old receiver instance from receivers
"""
try:
index = receivers.index(receiver)
# need to scan back references here and remove senderkey
except ValueError:
return False
else:
oldReceiver = receivers[index]
del receivers[index]
found = 0
signals = connections.get(signal)
if signals is not None:
for sig, recs in connections.get(signal, {}).iteritems():
if sig != signal:
for rec in recs:
if rec is oldReceiver:
found = 1
break
if not found:
_killBackref(oldReceiver, senderkey)
return True
return False
def _killBackref(receiver, senderkey):
"""Do the actual removal of back reference from receiver to senderkey"""
receiverkey = id(receiver)
set = sendersBack.get(receiverkey, ())
while senderkey in set:
try:
set.remove(senderkey)
except Exception:
break
if not set:
try:
del sendersBack[receiverkey]
except KeyError:
pass
return True
