#------------------------------------------------------------------------------
#
#  Copyright (c) 2005, Enthought, Inc.
#  All rights reserved.
#
#  This software is provided without warranty under the terms of the BSD
#  license included in enthought/LICENSE.txt and may be redistributed only
#  under the conditions described in the aforementioned license.  The license
#  is also available online at http://www.enthought.com/licenses/BSD.txt
#
#  Thanks for using Enthought open source!
#
#  Author:        David C. Morrill
#  Original Date: 06/21/2002
#
#  Refactored into a separate module: 07/04/2003
#
#------------------------------------------------------------------------------

""" Defines the classes needed to implement and support the Traits change
    notification mechanism.
"""

#-------------------------------------------------------------------------------
#  Imports:
#-------------------------------------------------------------------------------

from __future__ import absolute_import

import weakref
import traceback
import sys

from threading import local as thread_local

from threading \
    import Thread

from thread \
    import get_ident

from types \
    import MethodType

from .trait_base \
    import Uninitialized

from .trait_errors \
    import TraitNotificationError

#-------------------------------------------------------------------------------
#  Global Data:
#-------------------------------------------------------------------------------

# The thread ID for the user interface thread
ui_thread = -1

# The handler for notifications that must be run on the UI thread
ui_handler = None

#-------------------------------------------------------------------------------
#  Sets up the user interface thread handler:
#-------------------------------------------------------------------------------

def set_ui_handler ( handler ):
    """ Sets up the user interface thread handler.
    """
    global ui_handler, ui_thread

    ui_handler = handler
    ui_thread  = get_ident()

def ui_dispatch( handler, *args, **kw ):
    if get_ident() == ui_thread:
        handler( *args, **kw )
    else:
        ui_handler( handler, *args, **kw )

#-------------------------------------------------------------------------------
#  'NotificationExceptionHandlerState' class:
#-------------------------------------------------------------------------------

class NotificationExceptionHandlerState ( object ):

    def __init__ ( self, handler, reraise_exceptions, locked ):
        self.handler            = handler
        self.reraise_exceptions = reraise_exceptions
        self.locked             = locked

#-------------------------------------------------------------------------------
#  'NotificationExceptionHandler' class:
#-------------------------------------------------------------------------------

class NotificationExceptionHandler ( object ):

    def __init__ ( self ):
        self.traits_logger = None
        self.main_thread   = None
        self.thread_local  = thread_local()

#-- Private Methods ------------------------------------------------------------

    def _push_handler ( self, handler = None, reraise_exceptions = False,
                              main = False, locked = False ):
        """ Pushes a new traits notification exception handler onto the stack,
            making it the new exception handler. Returns a
            NotificationExceptionHandlerState object describing the previous
            exception handler.

            Parameters
            ----------
            handler : handler
                The new exception handler, which should be a callable or
                None. If None (the default), then the default traits
                notification exception handler is used. If *handler* is not
                None, then it must be a callable which can accept four
                arguments: object, trait_name, old_value, new_value.
            reraise_exceptions : Boolean
                Indicates whether exceptions should be reraised after the
                exception handler has executed. If True, exceptions will be
                re-raised after the specified handler has been executed.
                The default value is False.
            main : Boolean
                Indicates whether the caller represents the main application
                thread. If True, then the caller's exception handler is
                made the default handler for any other threads that are
                created. Note that a thread can explictly set its own exception
                handler if desired. The *main* flag is provided to make it
                easier to set a global application policy without having to
                explicitly set it for each thread. The default value is
                False.
            locked : Boolean
                Indicates whether further changes to the Traits notification
                exception handler state should be allowed. If True, then
                any subsequent calls to _push_handler() or _pop_handler() for
                that thread will raise a TraitNotificationError. The default
                value is False.
        """
        handlers = self._get_handlers()
        self._check_lock( handlers )
        if handler is None:
            handler = self._log_exception
        handlers.append( NotificationExceptionHandlerState( handler,
                                                  reraise_exceptions, locked ) )
        if main:
            self.main_thread = handlers

        return handlers[-2]

    def _pop_handler ( self ):
        """ Pops the traits notification exception handler stack, restoring
            the exception handler in effect prior to the most recent
            _push_handler() call. If the stack is empty or locked, a
            TraitNotificationError exception is raised.

            Note that each thread has its own independent stack. See the
            description of the _push_handler() method for more information on
            this.
        """
        handlers = self._get_handlers()
        self._check_lock( handlers )
        if len( handlers ) > 1:
            handlers.pop()
        else:
            raise TraitNotificationError(
                      'Attempted to pop an empty traits notification exception '
                      'handler stack.' )

    def _handle_exception ( self, object, trait_name, old, new  ):
        """ Handles a traits notification exception using the handler defined
            by the topmost stack entry for the corresponding thread.
        """
        excp_class, excp = sys.exc_info()[:2]
        handler_info     = self._get_handlers()[-1]
        handler_info.handler( object, trait_name, old, new )
        if (handler_info.reraise_exceptions or
            isinstance( excp, TraitNotificationError )):
            raise

    def _get_handlers ( self ):
        """ Returns the handler stack associated with the currently executing
            thread.
        """
        thread_local = self.thread_local
        if isinstance( thread_local, dict ):
            id       = get_ident()
            handlers = thread_local.get( id )
        else:
            handlers = getattr( thread_local, 'handlers', None )

        if handlers is None:
            if self.main_thread is not None:
                handler = self.main_thread[-1]
            else:
                handler = NotificationExceptionHandlerState(
                              self._log_exception, False, False )
            handlers = [ handler ]
            if isinstance( thread_local, dict ):
                thread_local[ id ] = handlers
            else:
                thread_local.handlers = handlers

        return handlers

    def _check_lock ( self, handlers ):
        """ Raises an exception if the specified handler stack is locked.
        """
        if handlers[-1].locked:
            raise TraitNotificationError(
                      'The traits notification exception handler is locked. '
                      'No changes are allowed.' )

    #---------------------------------------------------------------------------
    #  This method defines the default notification exception handling
    #  behavior of traits. However, it can be completely overridden by pushing
    #  a new handler using the '_push_handler' method.
    #
    #  It logs any exceptions generated in a trait notification handler.
    #---------------------------------------------------------------------------

    def _log_exception ( self, object, trait_name, old, new ):
        """ Logs any exceptions generated in a trait notification handler.
        """
        # When the stack depth is too great, the logger can't always log the
        # message. Make sure that it goes to the console at a minimum:
        excp_class, excp = sys.exc_info()[:2]
        if ((excp_class is RuntimeError) and
            (excp.args[0] == 'maximum recursion depth exceeded')):
            sys.__stderr__.write( 'Exception occurred in traits notification '
                'handler for object: %s, trait: %s, old value: %s, '
                'new value: %s.\n%s\n' % ( object, trait_name, old, new,
                ''.join( traceback.format_exception( *sys.exc_info() ) ) ) )

        logger = self.traits_logger
        if logger is None:
            import logging

            self.traits_logger = logger = logging.getLogger(
                                                  'traits' )
            handler = logging.StreamHandler()
            handler.setFormatter( logging.Formatter( '%(message)s' ) )
            logger.addHandler( handler )
            print ('Exception occurred in traits notification handler.\n'
                   'Please check the log file for details.')

        try:
            logger.exception(
                'Exception occurred in traits notification handler for '
                'object: %s, trait: %s, old value: %s, new value: %s' %
                ( object, trait_name, old, new ) )
        except Exception:
            # Ignore anything we can't log the above way:
            pass

#-------------------------------------------------------------------------------
#  Traits global notification exception handler:
#-------------------------------------------------------------------------------

notification_exception_handler = NotificationExceptionHandler()

push_exception_handler = notification_exception_handler._push_handler
pop_exception_handler  = notification_exception_handler._pop_handler
handle_exception       = notification_exception_handler._handle_exception

#-------------------------------------------------------------------------------
#  'StaticAnyTraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class StaticAnyTraitChangeNotifyWrapper:

    def __init__ ( self, handler ):
        n = handler.func_code.co_argcount
        if n > 4:
            raise TraitNotificationError(
                ('Invalid number of arguments for the static anytrait change '
                 'notification handler: %s. A maximum of 4 arguments is '
                 'allowed, but %s were specified.') % ( handler.__name__, n ) )

        self.handler  = handler
        self.call_method = 'call_%d' % n

    def __call__(self, object, trait_name, old, new):
        """ Dispatch to the appropriate method.

        We do explicit dispatch instead of assigning to the .__call__ instance
        attribute to avoid reference cycles.
        """
        getattr(self, self.call_method)(object, trait_name, old, new)

    def equals ( self, handler ):
        return False

    def call_0 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler()
            except:
                handle_exception( object, trait_name, old, new )

    def call_1 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object )
            except:
                handle_exception( object, trait_name, old, new )

    def call_2 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, trait_name )
            except:
                handle_exception( object, trait_name, old, new )

    def call_3 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_4 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, trait_name, old, new )
            except:
                handle_exception( object, trait_name, old, new )

#-------------------------------------------------------------------------------
#  'StaticTraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class StaticTraitChangeNotifyWrapper:

    def __init__ ( self, handler ):
        n = handler.func_code.co_argcount
        if n > 4:
            raise TraitNotificationError(
                ('Invalid number of arguments for the static trait change '
                 'notification handler: %s. A maximum of 4 arguments is '
                 'allowed, but %s were specified.') % ( handler.__name__, n ) )

        self.handler  = handler
        self.call_method = 'call_%d' % n

    def __call__(self, object, trait_name, old, new):
        """ Dispatch to the appropriate method.

        We do explicit dispatch instead of assigning to the .__call__ instance
        attribute to avoid reference cycles.
        """
        getattr(self, self.call_method)(object, trait_name, old, new)

    def equals ( self, handler ):
        return False

    def call_0 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler()
            except:
                handle_exception( object, trait_name, old, new )

    def call_1 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object )
            except:
                handle_exception( object, trait_name, old, new )

    def call_2 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_3 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, old, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_4 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.handler( object, trait_name, old, new )
            except:
                handle_exception( object, trait_name, old, new )

#-------------------------------------------------------------------------------
#  'TraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class TraitChangeNotifyWrapper:

    def __init__ ( self, handler, owner, target=None ):
        self.init( handler, owner, target )

    def init ( self, handler, owner, target=None ):
        # If target is not None and handler is a function
        # then the handler will be removed when target
        # is deleted.
        func = handler
        if type( handler ) is MethodType:
            func   = handler.im_func
            object = handler.im_self
            if object is not None:
                self.object = weakref.ref( object, self.listener_deleted )
                self.name   = handler.__name__
                self.owner  = owner
                arg_count   = func.func_code.co_argcount - 1
                if arg_count > 4:
                    raise TraitNotificationError(
                        ('Invalid number of arguments for the dynamic trait '
                         'change notification handler: %s. A maximum of 4 '
                         'arguments is allowed, but %s were specified.') %
                        ( func.__name__, arg_count ) )

                self.call_method = 'rebind_call_%d' % arg_count

                return arg_count
        elif target is not None:
            # Set up so the handler will be removed when the target
            # is deleted
            self.object = weakref.ref( target, self.listener_deleted )
            self.owner = owner

        arg_count = handler.func_code.co_argcount
        if arg_count > 4:
            raise TraitNotificationError(
                ('Invalid number of arguments for the dynamic trait change '
                 'notification handler: %s. A maximum of 4 arguments is '
                 'allowed, but %s were specified.') %
                ( handler.__name__, arg_count ) )

        self.name     = None
        self.handler  = handler
        self.call_method = 'call_%d' % arg_count

        return arg_count

    def __call__(self, object, trait_name, old, new):
        """ Dispatch to the appropriate method.

        We do explicit dispatch instead of assigning to the .__call__ instance
        attribute to avoid reference cycles.
        """
        getattr(self, self.call_method)(object, trait_name, old, new)

    # NOTE: This method is normally the only one that needs to be overridden in
    # a subclass to implement the subclass's dispatch mechanism:
    def dispatch ( self, handler, *args ):
        handler( *args )

    def equals ( self, handler ):
        if handler is self:
            return True

        if (type( handler ) is MethodType) and (handler.im_self is not None):
            return ((handler.__name__ == self.name) and
                    (handler.im_self is self.object()))

        return ((self.name is None) and (handler == self.handler))

    def listener_deleted ( self, ref ):
        self.owner.remove( self )
        self.object = self.owner = None

    def dispose ( self ):
        self.object = None

    def call_0 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.dispatch( self.handler )
            except:
                handle_exception( object, trait_name, old, new )

    def call_1 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.dispatch( self.handler, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_2 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.dispatch( self.handler, trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_3 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.dispatch( self.handler, object, trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def call_4 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            try:
                self.dispatch( self.handler, object, trait_name, old, new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_0 ( self, object, trait_name, old, new ):
        if (self.object is not None) and (old is not Uninitialized):
            try:
                self.dispatch( getattr( self.object(), self.name ) )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_1 ( self, object, trait_name, old, new ):
        if (self.object is not None) and (old is not Uninitialized):
            try:
                self.dispatch( getattr( self.object(), self.name ), new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_2 ( self, object, trait_name, old, new ):
        if (self.object is not None) and (old is not Uninitialized):
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_3 ( self, object, trait_name, old, new ):
        if (self.object is not None) and (old is not Uninitialized):
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               object, trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_4 ( self, object, trait_name, old, new ):
        if (self.object is not None) and (old is not Uninitialized):
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               object, trait_name, old, new )
            except:
                handle_exception( object, trait_name, old, new )

#-------------------------------------------------------------------------------
#  'ExtendedTraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class ExtendedTraitChangeNotifyWrapper ( TraitChangeNotifyWrapper ):

    def call_0 ( self, object, trait_name, old, new ):
        try:
            self.dispatch( self.handler )
        except:
            handle_exception( object, trait_name, old, new )

    def call_1 ( self, object, trait_name, old, new ):
        try:
            self.dispatch( self.handler, new )
        except:
            handle_exception( object, trait_name, old, new )

    def call_2 ( self, object, trait_name, old, new ):
        try:
            self.dispatch( self.handler, trait_name, new )
        except:
            handle_exception( object, trait_name, old, new )

    def call_3 ( self, object, trait_name, old, new ):
        try:
            self.dispatch( self.handler, object, trait_name, new )
        except:
            handle_exception( object, trait_name, old, new )

    def call_4 ( self, object, trait_name, old, new ):
        try:
            self.dispatch( self.handler, object, trait_name, old, new )
        except:
            handle_exception( object, trait_name, old, new )

    def rebind_call_0 ( self, object, trait_name, old, new ):
        if self.object is not None:
            try:
                self.dispatch( getattr( self.object(), self.name ) )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_1 ( self, object, trait_name, old, new ):
        if self.object is not None:
            try:
                self.dispatch( getattr( self.object(), self.name ), new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_2 ( self, object, trait_name, old, new ):
        if self.object is not None:
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_3 ( self, object, trait_name, old, new ):
        if self.object is not None:
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               object, trait_name, new )
            except:
                handle_exception( object, trait_name, old, new )

    def rebind_call_4 ( self, object, trait_name, old, new ):
        if self.object is not None:
            try:
                self.dispatch( getattr( self.object(), self.name ),
                               object, trait_name, old, new )
            except:
                handle_exception( object, trait_name, old, new )

#-------------------------------------------------------------------------------
#  'FastUITraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class FastUITraitChangeNotifyWrapper ( TraitChangeNotifyWrapper ):

    def dispatch ( self, handler, *args ):
        if get_ident() == ui_thread:
            handler( *args )
        else:
            ui_handler( handler, *args )

#-------------------------------------------------------------------------------
#  'UITraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class UITraitChangeNotifyWrapper ( TraitChangeNotifyWrapper ):

    def __init__ ( self, handler, owner, target ):
        self.init( handler, owner, target )
        self.deferred = None

    def call_0 ( self, object, trait_name, old, new ):
        if (old is not Uninitialized) and (self.deferred is None):
            self.deferred = DeferredTraitNotification( object, trait_name, old,
                                                       new )
            ui_handler( self.dispatch_0, self.deferred )

    def dispatch_0 ( self, deferred ):
        self.deferred = None
        try:
            self.handler()
        except:
            handle_exception( deferred.object, deferred.trait_name,
                              deferred.old, deferred.new )

    def call_1 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            if self.deferred is None:
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.dispatch_1, self.deferred )
            else:
                self.deferred.new = new

    def dispatch_1 ( self, deferred ):
        self.deferred = None
        try:
            self.handler( deferred.new )
        except:
            handle_exception( deferred.object, deferred.trait_name,
                              deferred.old, deferred.new )

    def call_2 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            if ((self.deferred is None) or
                (self.deferred.trait_name != trait_name)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.dispatch_2, self.deferred )
            else:
                self.deferred.new = new

    def dispatch_2 ( self, deferred ):
        self.deferred = None
        try:
            self.handler( deferred.trait_name, deferred.new )
        except:
            handle_exception( deferred.object, deferred.trait_name,
                              deferred.old, deferred.new )

    def call_3 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            deferred = self.deferred
            if ((deferred is None) or (deferred.trait_name != trait_name) or
                (deferred.object is not object)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.dispatch_3, self.deferred )
            else:
                self.deferred.new = new

    def dispatch_3 ( self, deferred ):
        self.deferred = None
        try:
            self.handler( deferred.object, deferred.trait_name, deferred.new )
        except:
            handle_exception( deferred.object, deferred.trait_name,
                              deferred.old, deferred.new )

    def call_4 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            deferred = self.deferred
            if ((deferred is None) or (deferred.trait_name != trait_name) or
                (deferred.object is not object)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.dispatch_4, self.deferred )
            else:
                self.deferred.new = new

    def dispatch_4 ( self, deferred ):
        self.deferred = None
        try:
            self.handler( deferred.object, deferred.trait_name, deferred.old,
                          deferred.new )
        except:
            handle_exception( deferred.object, deferred.trait_name,
                              deferred.old, deferred.new )

    def rebind_call_0 ( self, object, trait_name, old, new ):
        if (old is not Uninitialized) and (self.deferred is None):
            self.deferred = DeferredTraitNotification( object, trait_name, old,
                                                       new )
            ui_handler( self.rebind_dispatch_0, self.deferred )

    def rebind_dispatch_0 ( self, deferred ):
        self.deferred = None
        if self.object is not None:
            try:
                getattr( self.object(), self.name )()
            except:
                handle_exception( deferred.object, deferred.trait_name,
                                  deferred.old, deferred.new )

    def rebind_call_1 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            if self.deferred is None:
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.rebind_dispatch_1, self.deferred )
            else:
                self.deferred.new = new

    def rebind_dispatch_1 ( self, deferred ):
        self.deferred = None
        if self.object is not None:
            try:
                getattr( self.object(), self.name )( deferred.new )
            except:
                handle_exception( deferred.object, deferred.trait_name,
                                  deferred.old, deferred.new )

    def rebind_call_2 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            if ((self.deferred is None) or
                (self.deferred.trait_name != trait_name)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.rebind_dispatch_2, self.deferred )
            else:
                self.deferred.new = new

    def rebind_dispatch_2 ( self, deferred ):
        self.deferred = None
        if self.object is not None:
            try:
                getattr( self.object(), self.name )( deferred.trait_name,
                                                            deferred.new )
            except:
                handle_exception( deferred.object, deferred.trait_name,
                                  deferred.old, deferred.new )

    def rebind_call_3 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            deferred = self.deferred
            if ((deferred is None) or (deferred.trait_name != trait_name) or
                (deferred.object is not object)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.rebind_dispatch_3, self.deferred )
            else:
                self.deferred.new = new

    def rebind_dispatch_3 ( self, deferred ):
        self.deferred = None
        if self.object is not None:
            try:
                getattr( self.object(), self.name )( deferred.object,
                         deferred.trait_name, deferred.new )
            except:
                handle_exception( deferred.object, deferred.trait_name,
                                  deferred.old, deferred.new )

    def rebind_call_4 ( self, object, trait_name, old, new ):
        if old is not Uninitialized:
            deferred = self.deferred
            if ((deferred is None) or (deferred.trait_name != trait_name) or
                (deferred.object is not object)):
                self.deferred = DeferredTraitNotification( object, trait_name,
                                                           old, new )
                ui_handler( self.rebind_dispatch_4, self.deferred )
            else:
                self.deferred.new = new

    def rebind_dispatch_4 ( self, deferred ):
        self.deferred = None
        if self.object is not None:
            try:
                getattr( self.object(), self.name )( deferred.object,
                         deferred.trait_name, deferred.old, deferred.new )
            except:
                handle_exception( deferred.object, deferred.trait_name,
                                  deferred.old, deferred.new )

class DeferredTraitNotification ( object ):

    def __init__ ( self, object, trait_name, old, new ):
        self.object     = object
        self.trait_name = trait_name
        self.old        = old
        self.new        = new

#-------------------------------------------------------------------------------
#  'NewTraitChangeNotifyWrapper' class:
#-------------------------------------------------------------------------------

class NewTraitChangeNotifyWrapper ( TraitChangeNotifyWrapper ):

    def dispatch ( self, handler, *args ):
        Thread( target = handler, args = args ).start()

