dispatcher.py

"""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 types, weakref
import saferef, robustapply, errors

__author__   = "Patrick K. O'Brien <pobrien@orbtech.com>"
__cvsid__    = "$Id: dispatcher.py,v 2.1 2005/02/26 02:41:17 stuvi Exp $"
__version__  = "$Revision: 2.1 $"

try:
    True
except NameError:
    True = 1==1
    False = 1==0

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 = {}


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)
    )
  receiverID = id( receiver )
  if weak: receiver = saferef.safeRef(receiver, onDelete=_removeReceiver)
  senderkey = id(sender)
  signals = {}
  if connections.has_key(senderkey):
    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
        sendersBack.setdefault(receiverID,[]).append(senderkey)
      except:
        pass
  receivers = []
  if signals.has_key(signal):
    receivers = signals[signal]
  else:
    signals[signal] = receivers
  try: receivers.remove(receiver)
  except ValueError: pass
  receivers.append(receiver)

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:
    receivers = connections[senderkey][signal]
  except KeyError:
    raise errors.DispatcherKeyError(
      """No receivers found for signal %r from sender %r""" %(
        signal,
        sender
      )
    )
  try:
    receivers.remove(receiver)
  except ValueError:
    raise errors.DispatcherKeyError(
      """No connection to receiver %s for signal %s from sender %s""" %(
        receiver,
        signal,
        sender
      )
    )
  _cleanupConnections(senderkey, signal)

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 []

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

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 not receivers.has_key( receiver ):
            receivers[receiver] = 1
            yield receiver
        except TypeError:
          # dead weakrefs raise TypeError on hash...
          pass

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
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."""
  backKey = id(receiver)
  for senderkey in sendersBack.get(backKey,()):
    try:
      for signal in connections[senderkey].keys():
        try:
          receivers = connections[senderkey][signal]
        except KeyError:
          pass
        else:
          try: receivers.remove(receiver)
          except: pass
        _cleanupConnections(senderkey, signal)
    except KeyError:
      pass

def _cleanupConnections(senderkey, signal):
  """Delete any empty signals for senderkey. Delete senderkey if empty."""
  try:
    receivers = connections[senderkey][signal]
  except:
    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."""
  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: pass

---