Merge branch 'kernelmanager' of git://github.com/ellisonbg/ipython into qtfrontend. Fixed breakage and conflicts from merge.

Conflicts:
	IPython/frontend/qt/console/ipython_widget.py

IPython/frontend/qt/console/frontend_widget.py

@@ -1,330 +1,330 b''
 # Standard library imports
 import signal
 
 # System library imports
 from pygments.lexers import PythonLexer
 from PyQt4 import QtCore, QtGui
 import zmq
 
 # Local imports
 from IPython.core.inputsplitter import InputSplitter
 from call_tip_widget import CallTipWidget
 from completion_lexer import CompletionLexer
 from console_widget import HistoryConsoleWidget
 from pygments_highlighter import PygmentsHighlighter
 
 
 class FrontendHighlighter(PygmentsHighlighter):
     """ A Python PygmentsHighlighter that can be turned on and off and which 
         knows about continuation prompts.
     """
 
     def __init__(self, frontend):
         PygmentsHighlighter.__init__(self, frontend.document(), PythonLexer())
         self._current_offset = 0
         self._frontend = frontend
         self.highlighting_on = False
 
     def highlightBlock(self, qstring):
         """ Highlight a block of text. Reimplemented to highlight selectively.
         """
         if self.highlighting_on:
             for prompt in (self._frontend._continuation_prompt,
                            self._frontend._prompt):                           
                 if qstring.startsWith(prompt):
                     qstring.remove(0, len(prompt))
                     self._current_offset = len(prompt)
                     break
             PygmentsHighlighter.highlightBlock(self, qstring)
 
     def setFormat(self, start, count, format):
         """ Reimplemented to avoid highlighting continuation prompts.
         """
         start += self._current_offset
         PygmentsHighlighter.setFormat(self, start, count, format)
 
 
 class FrontendWidget(HistoryConsoleWidget):
     """ A Qt frontend for a generic Python kernel.
     """
 
     # Emitted when an 'execute_reply' is received from the kernel.
     executed = QtCore.pyqtSignal(object)
 
     #---------------------------------------------------------------------------
     # 'QObject' interface
     #---------------------------------------------------------------------------
     
     def __init__(self, parent=None):
         super(FrontendWidget, self).__init__(parent)
 
         # ConsoleWidget protected variables.
         self._continuation_prompt = '... '
         self._prompt = '>>> '
 
         # FrontendWidget protected variables.
         self._call_tip_widget = CallTipWidget(self)
         self._completion_lexer = CompletionLexer(PythonLexer())
         self._hidden = True
         self._highlighter = FrontendHighlighter(self)
         self._input_splitter = InputSplitter(input_mode='replace')
         self._kernel_manager = None
 
         self.document().contentsChange.connect(self._document_contents_change)
 
     #---------------------------------------------------------------------------
     # 'QWidget' interface
     #---------------------------------------------------------------------------
 
     def focusOutEvent(self, event):
         """ Reimplemented to hide calltips.
         """
         self._call_tip_widget.hide()
         super(FrontendWidget, self).focusOutEvent(event)
 
     def keyPressEvent(self, event):
         """ Reimplemented to allow calltips to process events and to send
             signals to the kernel.
         """
         if self._executing and event.key() == QtCore.Qt.Key_C and \
                 self._control_down(event.modifiers()):
             self._interrupt_kernel()
         else:
             if self._call_tip_widget.isVisible():
                 self._call_tip_widget.keyPressEvent(event)
             super(FrontendWidget, self).keyPressEvent(event)
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' abstract interface
     #---------------------------------------------------------------------------
 
     def _is_complete(self, source, interactive):
         """ Returns whether 'source' can be completely processed and a new
             prompt created. When triggered by an Enter/Return key press,
             'interactive' is True; otherwise, it is False.
         """
         complete = self._input_splitter.push(source)
         if interactive:
             complete = not self._input_splitter.push_accepts_more()
         return complete
 
     def _execute(self, source, hidden):
         """ Execute 'source'. If 'hidden', do not show any output.
         """
         self.kernel_manager.xreq_channel.execute(source)
         self._hidden = hidden
         
     def _prompt_started_hook(self):
         """ Called immediately after a new prompt is displayed.
         """
         self._highlighter.highlighting_on = True
 
         # Auto-indent if this is a continuation prompt.
         if self._get_prompt_cursor().blockNumber() != \
                 self._get_end_cursor().blockNumber():
             self.appendPlainText(' ' * self._input_splitter.indent_spaces)
 
     def _prompt_finished_hook(self):
         """ Called immediately after a prompt is finished, i.e. when some input
             will be processed and a new prompt displayed.
         """
         self._highlighter.highlighting_on = False
 
     def _tab_pressed(self):
         """ Called when the tab key is pressed. Returns whether to continue
             processing the event.
         """
         self._keep_cursor_in_buffer()
         cursor = self.textCursor()
         if not self._complete():
             cursor.insertText('    ')
         return False
 
     #---------------------------------------------------------------------------
     # 'FrontendWidget' interface
     #---------------------------------------------------------------------------
 
     def execute_file(self, path, hidden=False):
         """ Attempts to execute file with 'path'. If 'hidden', no output is
             shown.
         """
         self.execute('execfile("%s")' % path, hidden=hidden)
 
     def _get_kernel_manager(self):
         """ Returns the current kernel manager.
         """
         return self._kernel_manager
 
     def _set_kernel_manager(self, kernel_manager):
         """ Disconnect from the current kernel manager (if any) and set a new
             kernel manager.
         """
         # Disconnect the old kernel manager, if necessary.
         if self._kernel_manager is not None:
-            self._kernel_manager.started_listening.disconnect(
-                self._started_listening)
-            self._kernel_manager.stopped_listening.disconnect(
-                self._stopped_listening)
+            self._kernel_manager.started_channels.disconnect(
+                self._started_channels)
+            self._kernel_manager.stopped_channels.disconnect(
+                self._stopped_channels)
 
             # Disconnect the old kernel manager's channels.
             sub = self._kernel_manager.sub_channel
             xreq = self._kernel_manager.xreq_channel
             sub.message_received.disconnect(self._handle_sub)
             xreq.execute_reply.disconnect(self._handle_execute_reply)
             xreq.complete_reply.disconnect(self._handle_complete_reply)
             xreq.object_info_reply.disconnect(self._handle_object_info_reply)
 
-            # Handle the case where the old kernel manager is still listening.
-            if self._kernel_manager.is_listening:
-                self._stopped_listening()
+            # Handle the case where the old kernel manager is still channels.
+            if self._kernel_manager.channels_running:
+                self._stopped_channels()
 
         # Set the new kernel manager.
         self._kernel_manager = kernel_manager
         if kernel_manager is None:
             return
 
         # Connect the new kernel manager.
-        kernel_manager.started_listening.connect(self._started_listening)
-        kernel_manager.stopped_listening.connect(self._stopped_listening)
+        kernel_manager.started_channels.connect(self._started_channels)
+        kernel_manager.stopped_channels.connect(self._stopped_channels)
 
         # Connect the new kernel manager's channels.
         sub = kernel_manager.sub_channel
         xreq = kernel_manager.xreq_channel
         sub.message_received.connect(self._handle_sub)
         xreq.execute_reply.connect(self._handle_execute_reply)
         xreq.complete_reply.connect(self._handle_complete_reply)
         xreq.object_info_reply.connect(self._handle_object_info_reply)
         
-        # Handle the case where the kernel manager started listening before
+        # Handle the case where the kernel manager started channels before
         # we connected.
-        if kernel_manager.is_listening:
-            self._started_listening()
+        if kernel_manager.channels_running:
+            self._started_channels()
 
     kernel_manager = property(_get_kernel_manager, _set_kernel_manager)
 
     #---------------------------------------------------------------------------
     # 'FrontendWidget' protected interface
     #---------------------------------------------------------------------------
 
     def _call_tip(self):
         """ Shows a call tip, if appropriate, at the current cursor location.
         """
         # Decide if it makes sense to show a call tip
         cursor = self.textCursor()
         cursor.movePosition(QtGui.QTextCursor.Left)
         document = self.document()
         if document.characterAt(cursor.position()).toAscii() != '(':
             return False
         context = self._get_context(cursor)
         if not context:
             return False
 
         # Send the metadata request to the kernel
         name = '.'.join(context)
         self._calltip_id = self.kernel_manager.xreq_channel.object_info(name)
         self._calltip_pos = self.textCursor().position()
         return True
 
     def _complete(self):
         """ Performs completion at the current cursor location.
         """
         # Decide if it makes sense to do completion
         context = self._get_context()
         if not context:
             return False
 
         # Send the completion request to the kernel
         text = '.'.join(context)
         self._complete_id = self.kernel_manager.xreq_channel.complete(
             text, self.input_buffer_cursor_line, self.input_buffer)
         self._complete_pos = self.textCursor().position()
         return True
 
     def _get_context(self, cursor=None):
         """ Gets the context at the current cursor location.
         """
         if cursor is None:
             cursor = self.textCursor()
         cursor.movePosition(QtGui.QTextCursor.StartOfLine, 
                             QtGui.QTextCursor.KeepAnchor)
         text = unicode(cursor.selectedText())
         return self._completion_lexer.get_context(text)
 
     def _interrupt_kernel(self):
         """ Attempts to the interrupt the kernel.
         """
         if self.kernel_manager.has_kernel:
             self.kernel_manager.signal_kernel(signal.SIGINT)
         else:
             self.appendPlainText('Kernel process is either remote or '
                                  'unspecified. Cannot interrupt.\n')
 
     #------ Signal handlers ----------------------------------------------------
 
     def _document_contents_change(self, position, removed, added):
         """ Called whenever the document's content changes. Display a calltip
             if appropriate.
         """
         # Calculate where the cursor should be *after* the change:
         position += added
 
         document = self.document()
         if position == self.textCursor().position():
             self._call_tip()
 
     def _handle_sub(self, omsg):
         if self._hidden:
             return
         handler = getattr(self, '_handle_%s' % omsg['msg_type'], None)
         if handler is not None:
             handler(omsg)
 
     def _handle_pyout(self, omsg):
         session = omsg['parent_header']['session']
         if session == self.kernel_manager.session.session:
             self.appendPlainText(omsg['content']['data'] + '\n')
 
     def _handle_stream(self, omsg):
         self.appendPlainText(omsg['content']['data'])
         self.moveCursor(QtGui.QTextCursor.End)
         
     def _handle_execute_reply(self, rep):
         if self._hidden:
             return
 
         # Make sure that all output from the SUB channel has been processed
         # before writing a new prompt.
         self.kernel_manager.sub_channel.flush()
 
         content = rep['content']
         status = content['status']
         if status == 'error':
             self.appendPlainText(content['traceback'][-1])
         elif status == 'aborted':
             text = "ERROR: ABORTED\n"
             self.appendPlainText(text)
         self._hidden = True
         self._show_prompt()
         self.executed.emit(rep)
 
     def _handle_complete_reply(self, rep):
         cursor = self.textCursor()
         if rep['parent_header']['msg_id'] == self._complete_id and \
                 cursor.position() == self._complete_pos:
             text = '.'.join(self._get_context())
             cursor.movePosition(QtGui.QTextCursor.Left, n=len(text))
             self._complete_with_items(cursor, rep['content']['matches'])
 
     def _handle_object_info_reply(self, rep):
         cursor = self.textCursor()
         if rep['parent_header']['msg_id'] == self._calltip_id and \
                 cursor.position() == self._calltip_pos:
             doc = rep['content']['docstring']
             if doc:
                 self._call_tip_widget.show_docstring(doc)
 
-    def _started_listening(self):
+    def _started_channels(self):
         self.clear()
 
-    def _stopped_listening(self):
+    def _stopped_channels(self):
         pass

IPython/frontend/qt/console/ipython_widget.py

@@ -1,94 +1,94 b''
 # System library imports
 from PyQt4 import QtCore, QtGui
 
 # Local imports
 from frontend_widget import FrontendWidget
 
 
 class IPythonWidget(FrontendWidget):
     """ A FrontendWidget for an IPython kernel.
     """
 
     #---------------------------------------------------------------------------
     # 'QObject' interface
     #---------------------------------------------------------------------------
     
     def __init__(self, parent=None):
         super(IPythonWidget, self).__init__(parent)
 
         self._magic_overrides = {}
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' abstract interface
     #---------------------------------------------------------------------------
 
     def _execute(self, source, hidden):
         """ Reimplemented to override magic commands.
         """
         magic_source = source.strip()
         if magic_source.startswith('%'):
             magic_source = magic_source[1:]
         magic, sep, arguments = magic_source.partition(' ')
         if not magic:
             magic = magic_source
 
         callback = self._magic_overrides.get(magic)
         if callback:
             output = callback(arguments)
             if output:
                 self.appendPlainText(output)
             self._show_prompt()
         else:
             super(IPythonWidget, self)._execute(source, hidden)
 
     #---------------------------------------------------------------------------
     # 'FrontendWidget' interface
     #---------------------------------------------------------------------------
 
     def execute_file(self, path, hidden=False):
         """ Reimplemented to use the 'run' magic.
         """
         self.execute('run %s' % path, hidden=hidden)
 
     #---------------------------------------------------------------------------
     # 'IPythonWidget' interface
     #---------------------------------------------------------------------------
 
     def set_magic_override(self, magic, callback):
         """ Overrides an IPython magic command. This magic will be intercepted
             by the frontend rather than passed on to the kernel and 'callback'
             will be called with a single argument: a string of argument(s) for
             the magic. The callback can (optionally) return text to print to the
             console.
         """
         self._magic_overrides[magic] = callback
 
     def remove_magic_override(self, magic):
         """ Removes the override for the specified magic, if there is one.
         """
         try:
             del self._magic_overrides[magic]
         except KeyError:
             pass
 
 
 if __name__ == '__main__':
     from IPython.frontend.qt.kernelmanager import QtKernelManager
 
     # Don't let Qt or ZMQ swallow KeyboardInterupts.
     import signal
     signal.signal(signal.SIGINT, signal.SIG_DFL)
 
     # Create a KernelManager.
     kernel_manager = QtKernelManager()
     kernel_manager.start_kernel()
-    kernel_manager.start_listening()
+    kernel_manager.start_channels()
 
     # Launch the application.
     app = QtGui.QApplication([])
     widget = IPythonWidget()
     widget.kernel_manager = kernel_manager
     widget.setWindowTitle('Python')
     widget.resize(640, 480)
     widget.show()
     app.exec_()

IPython/frontend/qt/kernelmanager.py

@@ -1,147 +1,151 b''
 """ Defines a KernelManager that provides signals and slots.
 """
 
 # System library imports.
 from PyQt4 import QtCore
 import zmq
 
 # IPython imports.
 from IPython.zmq.kernelmanager import KernelManager, SubSocketChannel, \
     XReqSocketChannel, RepSocketChannel
 from util import MetaQObjectHasTraits
 
 
 
 class QtSubSocketChannel(SubSocketChannel, QtCore.QObject):
 
     # Emitted when any message is received.
     message_received = QtCore.pyqtSignal(object)
 
     # Emitted when a message of type 'pyout' or 'stdout' is received.
     output_received = QtCore.pyqtSignal(object)
 
     # Emitted when a message of type 'pyerr' or 'stderr' is received.
     error_received = QtCore.pyqtSignal(object)
 
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
     
     def __init__(self, *args, **kw):
         """ Reimplemented to ensure that QtCore.QObject is initialized first.
         """
         QtCore.QObject.__init__(self)
         SubSocketChannel.__init__(self, *args, **kw)
 
     #---------------------------------------------------------------------------
     # 'SubSocketChannel' interface
     #---------------------------------------------------------------------------
     
     def call_handlers(self, msg):
         """ Reimplemented to emit signals instead of making callbacks.
         """
         # Emit the generic signal.
         self.message_received.emit(msg)
         
         # Emit signals for specialized message types.
         msg_type = msg['msg_type']
         if msg_type in ('pyout', 'stdout'):
             self.output_received.emit(msg)
         elif msg_type in ('pyerr', 'stderr'):
             self.error_received.emit(msg)
 
     def flush(self):
         """ Reimplemented to ensure that signals are dispatched immediately.
         """
         super(QtSubSocketChannel, self).flush()
         QtCore.QCoreApplication.instance().processEvents()
 
 
 class QtXReqSocketChannel(XReqSocketChannel, QtCore.QObject):
 
     # Emitted when any message is received.
     message_received = QtCore.pyqtSignal(object)
 
     # Emitted when a reply has been received for the corresponding request type.
     execute_reply = QtCore.pyqtSignal(object)
     complete_reply = QtCore.pyqtSignal(object)
     object_info_reply = QtCore.pyqtSignal(object)
 
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
     
     def __init__(self, *args, **kw):
         """ Reimplemented to ensure that QtCore.QObject is initialized first.
         """
         QtCore.QObject.__init__(self)
         XReqSocketChannel.__init__(self, *args, **kw)
     
     #---------------------------------------------------------------------------
     # 'XReqSocketChannel' interface
     #---------------------------------------------------------------------------
     
     def call_handlers(self, msg):
         """ Reimplemented to emit signals instead of making callbacks.
         """
         # Emit the generic signal.
         self.message_received.emit(msg)
         
         # Emit signals for specialized message types.
         msg_type = msg['msg_type']
         signal = getattr(self, msg_type, None)
         if signal:
             signal.emit(msg)
 
-    def _queue_request(self, msg, callback):
-        """ Reimplemented to skip callback handling.
-        """
-        self.command_queue.put(msg)
-        self.add_io_state(zmq.POLLOUT)
-
 
 class QtRepSocketChannel(RepSocketChannel, QtCore.QObject):
 
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
     
     def __init__(self, *args, **kw):
         """ Reimplemented to ensure that QtCore.QObject is initialized first.
         """
         QtCore.QObject.__init__(self)
         RepSocketChannel.__init__(self, *args, **kw)
 
 
 class QtKernelManager(KernelManager, QtCore.QObject):
     """ A KernelManager that provides signals and slots.
     """
 
     __metaclass__ = MetaQObjectHasTraits
 
     # Emitted when the kernel manager has started listening.
-    started_listening = QtCore.pyqtSignal()
+    started_channels = QtCore.pyqtSignal()
 
     # Emitted when the kernel manager has stopped listening.
-    stopped_listening = QtCore.pyqtSignal()
+    stopped_channels = QtCore.pyqtSignal()
 
     # Use Qt-specific channel classes that emit signals.
     sub_channel_class = QtSubSocketChannel
     xreq_channel_class = QtXReqSocketChannel
     rep_channel_class = QtRepSocketChannel
 
     #---------------------------------------------------------------------------
+    # 'object' interface
+    #---------------------------------------------------------------------------
+    
+    def __init__(self, *args, **kw):
+        """ Reimplemented to ensure that QtCore.QObject is initialized first.
+        """
+        QtCore.QObject.__init__(self)
+        KernelManager.__init__(self, *args, **kw)
+
+    #---------------------------------------------------------------------------
     # 'KernelManager' interface
     #---------------------------------------------------------------------------
     
-    def start_listening(self):
+    def start_channels(self):
         """ Reimplemented to emit signal.
         """
-        super(QtKernelManager, self).start_listening()
-        self.started_listening.emit()
+        super(QtKernelManager, self).start_channels()
+        self.started_channels.emit()
 
-    def stop_listening(self):
+    def stop_channels(self):
         """ Reimplemented to emit signal.
         """ 
-        super(QtKernelManager, self).stop_listening()
-        self.stopped_listening.emit()
+        super(QtKernelManager, self).stop_channels()
+        self.stopped_channels.emit()

IPython/zmq/kernelmanager.py

@@ -1,497 +1,536 b''
-"""Kernel frontend classes.
+"""Classes to manage the interaction with a running kernel.
 
-TODO: Create logger to handle debugging and console messages.
+Todo
+====
 
+* Create logger to handle debugging and console messages.
 """
 
+#-----------------------------------------------------------------------------
+#  Copyright (C) 2008-2010  The IPython Development Team
+#
+#  Distributed under the terms of the BSD License.  The full license is in
+#  the file COPYING, distributed as part of this software.
+#-----------------------------------------------------------------------------
+
+#-----------------------------------------------------------------------------
+# Imports
+#-----------------------------------------------------------------------------
+
 # Standard library imports.
 from Queue import Queue, Empty
 from subprocess import Popen
 from threading import Thread
 import time
-import traceback
 
 # System library imports.
 import zmq
 from zmq import POLLIN, POLLOUT, POLLERR
 from zmq.eventloop import ioloop
 
 # Local imports.
-from IPython.utils.traitlets import HasTraits, Any, Bool, Int, Instance, Str, \
-    Type
+from IPython.utils.traitlets import HasTraits, Any, Instance, Type
 from kernel import launch_kernel
 from session import Session
 
-# Constants.
-LOCALHOST = '127.0.0.1'
+#-----------------------------------------------------------------------------
+# Constants and exceptions
+#-----------------------------------------------------------------------------
 
+LOCALHOST = '127.0.0.1'
 
-class MissingHandlerError(Exception):
+class InvalidPortNumber(Exception):
     pass
 
+#-----------------------------------------------------------------------------
+# ZMQ Socket Channel classes
+#-----------------------------------------------------------------------------
 
 class ZmqSocketChannel(Thread):
     """ The base class for the channels that use ZMQ sockets.
     """
-
     context = None
     session = None
     socket = None
     ioloop = None
     iostate = None
+    _address = None
+
+    def __init__(self, context, session, address):
+        """Create a channel
 
-    def __init__(self, context, session, address=None):
+        Parameters
+        ----------
+        context : zmq.Context
+            The ZMQ context to use.
+        session : session.Session
+            The session to use.
+        address : tuple
+            Standard (ip, port) tuple that the kernel is listening on.
+        """
         super(ZmqSocketChannel, self).__init__()
         self.daemon = True
 
         self.context = context
         self.session = session
-        self.address = address
+        if address[1] == 0:
+            raise InvalidPortNumber('The port number for a channel cannot be 0.')
+        self._address = address
 
     def stop(self):
-        """Stop the thread's activity. Returns when the thread terminates.
+        """Stop the channel's activity.
 
-        The thread will raise :class:`RuntimeError` if :method:`self.start`
-        is called again.
+        This calls :method:`Thread.join` and returns when the thread
+        terminates. :class:`RuntimeError` will be raised if 
+        :method:`self.start` is called again.
         """
         self.join()
 
+    @property
+    def address(self):
+        """Get the channel's address as an (ip, port) tuple.
 
-    def get_address(self):
-        """ Get the channel's address. By the default, a channel is on 
-            localhost with no port specified (a negative port number).
+        By the default, the address is (localhost, 0), where 0 means a random
+        port.
         """
         return self._address
 
-    def set_adresss(self, address):
-        """ Set the channel's address. Should be a tuple of form:
-                (ip address [str], port [int]).
-            or None, in which case the address is reset to its default value.
-        """
-        # FIXME: Validate address.
-        if self.is_alive():  # This is Thread.is_alive
-            raise RuntimeError("Cannot set address on a running channel!")
-        else:
-            if address is None:
-                address = (LOCALHOST, 0)
-            self._address = address
-
-    address = property(get_address, set_adresss)
-
     def add_io_state(self, state):
         """Add IO state to the eventloop.
 
+        Parameters
+        ----------
+        state : zmq.POLLIN|zmq.POLLOUT|zmq.POLLERR
+            The IO state flag to set.
+
         This is thread safe as it uses the thread safe IOLoop.add_callback.
         """
         def add_io_state_callback():
             if not self.iostate & state:
                 self.iostate = self.iostate | state
                 self.ioloop.update_handler(self.socket, self.iostate)
         self.ioloop.add_callback(add_io_state_callback)
 
     def drop_io_state(self, state):
         """Drop IO state from the eventloop.
 
+        Parameters
+        ----------
+        state : zmq.POLLIN|zmq.POLLOUT|zmq.POLLERR
+            The IO state flag to set.
+
         This is thread safe as it uses the thread safe IOLoop.add_callback.
         """
         def drop_io_state_callback():
             if self.iostate & state:
                 self.iostate = self.iostate & (~state)
                 self.ioloop.update_handler(self.socket, self.iostate)
         self.ioloop.add_callback(drop_io_state_callback)
 
 
-class SubSocketChannel(ZmqSocketChannel):
+class XReqSocketChannel(ZmqSocketChannel):
+    """The XREQ channel for issues request/replies to the kernel.
+    """
 
-    def __init__(self, context, session, address=None):
-        super(SubSocketChannel, self).__init__(context, session, address)
+    command_queue = None
+
+    def __init__(self, context, session, address):
+        self.command_queue = Queue()
+        super(XReqSocketChannel, self).__init__(context, session, address)
 
     def run(self):
-        self.socket = self.context.socket(zmq.SUB)
-        self.socket.setsockopt(zmq.SUBSCRIBE,'')
+        """The thread's main activity.  Call start() instead."""
+        self.socket = self.context.socket(zmq.XREQ)
         self.socket.setsockopt(zmq.IDENTITY, self.session.session)
         self.socket.connect('tcp://%s:%i' % self.address)
         self.ioloop = ioloop.IOLoop()
-        self.iostate = POLLIN|POLLERR
+        self.iostate = POLLERR|POLLIN
         self.ioloop.add_handler(self.socket, self._handle_events, 
                                 self.iostate)
         self.ioloop.start()
 
     def stop(self):
         self.ioloop.stop()
-        super(SubSocketChannel, self).stop()
-
-    def _handle_events(self, socket, events):
-        # Turn on and off POLLOUT depending on if we have made a request
-        if events & POLLERR:
-            self._handle_err()
-        if events & POLLIN:
-            self._handle_recv()
-
-    def _handle_err(self):
-        # We don't want to let this go silently, so eventually we should log.
-        raise zmq.ZMQError()
-
-    def _handle_recv(self):
-        # Get all of the messages we can
-        while True:
-            try:
-                msg = self.socket.recv_json(zmq.NOBLOCK)
-            except zmq.ZMQError:
-                # Check the errno?
-                # Will this tigger POLLERR?
-                break
-            else:
-                self.call_handlers(msg)
+        super(XReqSocketChannel, self).stop()
 
     def call_handlers(self, msg):
         """This method is called in the ioloop thread when a message arrives.
 
         Subclasses should override this method to handle incoming messages.
         It is important to remember that this method is called in the thread
         so that some logic must be done to ensure that the application leve
         handlers are called in the application thread.
         """
         raise NotImplementedError('call_handlers must be defined in a subclass.')
 
-    def flush(self, timeout=1.0):
-        """Immediately processes all pending messages on the SUB channel.
-
-        This method is thread safe.
+    def execute(self, code):
+        """Execute code in the kernel.
 
         Parameters
         ----------
-        timeout : float, optional
-            The maximum amount of time to spend flushing, in seconds. The
-            default is one second.
-        """
-        # We do the IOLoop callback process twice to ensure that the IOLoop
-        # gets to perform at least one full poll.
-        stop_time = time.time() + timeout
-        for i in xrange(2):
-            self._flushed = False
-            self.ioloop.add_callback(self._flush)
-            while not self._flushed and time.time() < stop_time:
-                time.sleep(0.01)
+        code : str
+            A string of Python code.
         
-    def _flush(self):
-        """Called in this thread by the IOLoop to indicate that all events have
-        been processed.
+        Returns
+        -------
+        The msg_id of the message sent.
         """
-        self._flushed = True
+        # Create class for content/msg creation. Related to, but possibly
+        # not in Session.
+        content = dict(code=code)
+        msg = self.session.msg('execute_request', content)
+        self._queue_request(msg)
+        return msg['header']['msg_id']
 
+    def complete(self, text, line, block=None):
+        """Tab complete text, line, block in the kernel's namespace.
 
-class XReqSocketChannel(ZmqSocketChannel):
+        Parameters
+        ----------
+        text : str
+            The text to complete.
+        line : str
+            The full line of text that is the surrounding context for the 
+            text to complete.
+        block : str
+            The full block of code in which the completion is being requested.
+
+        Returns
+        -------
+        The msg_id of the message sent.
 
-    handler_queue = None
-    command_queue = None
-    handlers = None
-    _overriden_call_handler = None
+        """
+        content = dict(text=text, line=line)
+        msg = self.session.msg('complete_request', content)
+        self._queue_request(msg)
+        return msg['header']['msg_id']
 
-    def __init__(self, context, session, address=None):
-        self.handlers = {}
-        self.handler_queue = Queue()
-        self.command_queue = Queue()
-        super(XReqSocketChannel, self).__init__(context, session, address)
+    def object_info(self, oname):
+        """Get metadata information about an object.
 
-    def run(self):
-        self.socket = self.context.socket(zmq.XREQ)
-        self.socket.setsockopt(zmq.IDENTITY, self.session.session)
-        self.socket.connect('tcp://%s:%i' % self.address)
-        self.ioloop = ioloop.IOLoop()
-        self.iostate = POLLERR|POLLIN
-        self.ioloop.add_handler(self.socket, self._handle_events, 
-                                self.iostate)
-        self.ioloop.start()
+        Parameters
+        ----------
+        oname : str
+            A string specifying the object name.
 
-    def stop(self):
-        self.ioloop.stop()
-        super(XReqSocketChannel, self).stop()
+        Returns
+        -------
+        The msg_id of the message sent.
+        """
+        print oname
+        content = dict(oname=oname)
+        msg = self.session.msg('object_info_request', content)
+        self._queue_request(msg)
+        return msg['header']['msg_id']
 
     def _handle_events(self, socket, events):
         if events & POLLERR:
             self._handle_err()
         if events & POLLOUT:
             self._handle_send()
         if events & POLLIN:
             self._handle_recv()
 
     def _handle_recv(self):
         msg = self.socket.recv_json()
         self.call_handlers(msg)
 
     def _handle_send(self):
         try:
             msg = self.command_queue.get(False)
         except Empty:
             pass
         else:
             self.socket.send_json(msg)
         if self.command_queue.empty():
             self.drop_io_state(POLLOUT)
 
     def _handle_err(self):
         # We don't want to let this go silently, so eventually we should log.
         raise zmq.ZMQError()
 
-    def _queue_request(self, msg, callback):
-        handler = self._find_handler(msg['msg_type'], callback)
-        self.handler_queue.put(handler)
+    def _queue_request(self, msg):
         self.command_queue.put(msg)
         self.add_io_state(POLLOUT)
 
-    def execute(self, code, callback=None):
-        # Create class for content/msg creation. Related to, but possibly
-        # not in Session.
-        content = dict(code=code)
-        msg = self.session.msg('execute_request', content)
-        self._queue_request(msg, callback)
-        return msg['header']['msg_id']
 
-    def complete(self, text, line, block=None, callback=None):
-        content = dict(text=text, line=line)
-        msg = self.session.msg('complete_request', content)
-        self._queue_request(msg, callback)
-        return msg['header']['msg_id']
+class SubSocketChannel(ZmqSocketChannel):
+    """The SUB channel which listens for messages that the kernel publishes.
+    """
 
-    def object_info(self, oname, callback=None):
-        content = dict(oname=oname)
-        msg = self.session.msg('object_info_request', content)
-        self._queue_request(msg, callback)
-        return msg['header']['msg_id']
+    def __init__(self, context, session, address):
+        super(SubSocketChannel, self).__init__(context, session, address)
 
-    def _find_handler(self, name, callback):
-        if callback is not None:
-            return callback
-        handler = self.handlers.get(name)
-        if handler is None:
-            raise MissingHandlerError(
-                'No handler defined for method: %s' % name)
-        return handler
+    def run(self):
+        """The thread's main activity.  Call start() instead."""
+        self.socket = self.context.socket(zmq.SUB)
+        self.socket.setsockopt(zmq.SUBSCRIBE,'')
+        self.socket.setsockopt(zmq.IDENTITY, self.session.session)
+        self.socket.connect('tcp://%s:%i' % self.address)
+        self.ioloop = ioloop.IOLoop()
+        self.iostate = POLLIN|POLLERR
+        self.ioloop.add_handler(self.socket, self._handle_events, 
+                                self.iostate)
+        self.ioloop.start()
 
-    def override_call_handler(self, func):
-        """Permanently override the call_handler.
+    def stop(self):
+        self.ioloop.stop()
+        super(SubSocketChannel, self).stop()
     
-        The function func will be called as::
+    def call_handlers(self, msg):
+        """This method is called in the ioloop thread when a message arrives.
 
-            func(handler, msg)
+        Subclasses should override this method to handle incoming messages.
+        It is important to remember that this method is called in the thread
+        so that some logic must be done to ensure that the application leve
+        handlers are called in the application thread.
+        """
+        raise NotImplementedError('call_handlers must be defined in a subclass.')
 
-        And must call::
+    def flush(self, timeout=1.0):
+        """Immediately processes all pending messages on the SUB channel.
         
-            handler(msg)
+        This method is thread safe.
 
-        in the main thread.
+        Parameters
+        ----------
+        timeout : float, optional
+            The maximum amount of time to spend flushing, in seconds. The
+            default is one second.
         """
-        assert callable(func), "not a callable: %r" % func
-        self._overriden_call_handler = func
+        # We do the IOLoop callback process twice to ensure that the IOLoop
+        # gets to perform at least one full poll.
+        stop_time = time.time() + timeout
+        for i in xrange(2):
+            self._flushed = False
+            self.ioloop.add_callback(self._flush)
+            while not self._flushed and time.time() < stop_time:
+                time.sleep(0.01)
 
-    def call_handlers(self, msg):
+    def _handle_events(self, socket, events):
+        # Turn on and off POLLOUT depending on if we have made a request
+        if events & POLLERR:
+            self._handle_err()
+        if events & POLLIN:
+            self._handle_recv()
+
+    def _handle_err(self):
+        # We don't want to let this go silently, so eventually we should log.
+        raise zmq.ZMQError()
+
+    def _handle_recv(self):
+        # Get all of the messages we can
+        while True:
         try:
-            handler = self.handler_queue.get(False)
-        except Empty:
-            print "Message received with no handler!!!"
-            print msg
-        else:
-            self.call_handler(handler, msg)
-
-    def call_handler(self, handler, msg):
-        if self._overriden_call_handler is not None:
-            self._overriden_call_handler(handler, msg)
-        elif hasattr(self, '_call_handler'):
-           call_handler = getattr(self, '_call_handler')
-           call_handler(handler, msg)
+                msg = self.socket.recv_json(zmq.NOBLOCK)
+            except zmq.ZMQError:
+                # Check the errno?
+                # Will this tigger POLLERR?
+                break
         else:
-            raise RuntimeError('no handler!')
+                self.call_handlers(msg)
+
+    def _flush(self):
+        """Callback for :method:`self.flush`."""
+        self._flushed = True
 
 
 class RepSocketChannel(ZmqSocketChannel):
+    """A reply channel to handle raw_input requests that the kernel makes."""
+
+    def run(self):
+        """The thread's main activity.  Call start() instead."""
+        self.ioloop = ioloop.IOLoop()
+        self.ioloop.start()
+
+    def stop(self):
+        self.ioloop.stop()
+        super(SubSocketChannel, self).stop()
 
     def on_raw_input(self):
         pass
 
 
+#-----------------------------------------------------------------------------
+# Main kernel manager class
+#-----------------------------------------------------------------------------
+
+
 class KernelManager(HasTraits):
     """ Manages a kernel for a frontend.
 
     The SUB channel is for the frontend to receive messages published by the
     kernel.
         
     The REQ channel is for the frontend to make requests of the kernel.
     
     The REP channel is for the kernel to request stdin (raw_input) from the
     frontend.
     """
-
-    # Whether the kernel manager is currently listening on its channels.
-    is_listening = Bool(False)
-
     # The PyZMQ Context to use for communication with the kernel.
-    context = Instance(zmq.Context, ())
+    context = Instance(zmq.Context)
 
     # The Session to use for communication with the kernel.
-    session = Instance(Session, ())
+    session = Instance(Session)
 
     # The classes to use for the various channels.
-    sub_channel_class = Type(SubSocketChannel)
     xreq_channel_class = Type(XReqSocketChannel)
+    sub_channel_class = Type(SubSocketChannel)
     rep_channel_class = Type(RepSocketChannel)
     
     # Protected traits.
     _kernel = Instance(Popen)
-    _sub_channel = Any
+    _xreq_address = Any
+    _sub_address = Any
+    _rep_address = Any
     _xreq_channel = Any
+    _sub_channel = Any
     _rep_channel = Any
 
+    def __init__(self, xreq_address=None, sub_address=None, rep_address=None,
+                 context=None, session=None):
+        self._xreq_address = (LOCALHOST, 0) if xreq_address is None else xreq_address
+        self._sub_address = (LOCALHOST, 0) if sub_address is None else sub_address
+        self._rep_address = (LOCALHOST, 0) if rep_address is None else rep_address
+        self.context = zmq.Context() if context is None else context
+        self.session = Session() if session is None else session
+
     #--------------------------------------------------------------------------
     # Channel management methods:
     #--------------------------------------------------------------------------
 
-    def start_listening(self):
-        """Starts listening on the specified ports. If already listening, raises
-        a RuntimeError.
+    def start_channels(self):
+        """Starts the channels for this kernel.
+
+        This will create the channels if they do not exist and then start
+        them. If port numbers of 0 are being used (random ports) then you
+        must first call :method:`start_kernel`. If the channels have been
+        stopped and you call this, :class:`RuntimeError` will be raised.
         """
-        if self.is_listening:
-            raise RuntimeError("Cannot start listening. Already listening!")
-        else:
-            self.is_listening = True
-            self.sub_channel.start()
             self.xreq_channel.start()
+        self.sub_channel.start()
             self.rep_channel.start()
 
-    @property
-    def is_alive(self):
-        """ Returns whether the kernel is alive. """
-        if self.is_listening:
-            # TODO: check if alive.
-            return True
-        else:
-            return False
+    def stop_channels(self):
+        """Stops the channels for this kernel.
 
-    def stop_listening(self):
-        """Stops listening. If not listening, does nothing. """
-        if self.is_listening:
-            self.is_listening = False
-            self.sub_channel.stop()
+        This stops the channels by joining their threads. If the channels
+        were not started, :class:`RuntimeError` will be raised.
+        """
             self.xreq_channel.stop()
+        self.sub_channel.stop()
             self.rep_channel.stop()
 
+    @property
+    def channels_running(self):
+        """Are all of the channels created and running?"""
+        return self.xreq_channel.is_alive() \
+            and self.sub_channel.is_alive() \
+            and self.rep_channel.is_alive()
+
     #--------------------------------------------------------------------------
     # Kernel process management methods:
     #--------------------------------------------------------------------------
 
     def start_kernel(self):
         """Starts a kernel process and configures the manager to use it.
 
-        If ports have been specified via the address attributes, they are used.
-        Otherwise, open ports are chosen by the OS and the channel port
-        attributes are configured as appropriate.
+        If random ports (port=0) are being used, this method must be called
+        before the channels are created.
         """
         xreq, sub = self.xreq_address, self.sub_address
         if xreq[0] != LOCALHOST or sub[0] != LOCALHOST:
             raise RuntimeError("Can only launch a kernel on localhost."
                                "Make sure that the '*_address' attributes are "
                                "configured properly.")
 
         kernel, xrep, pub = launch_kernel(xrep_port=xreq[1], pub_port=sub[1])
-        self.set_kernel(kernel)
-        self.xreq_address = (LOCALHOST, xrep)
-        self.sub_address = (LOCALHOST, pub)
-
-    def set_kernel(self, kernel):
-        """Sets the kernel manager's kernel to an existing kernel process.
-
-        It is *not* necessary to a set a kernel to communicate with it via the
-        channels, and those objects must be configured separately. It
-        *is* necessary to set a kernel if you want to use the manager (or
-        frontends that use the manager) to signal and/or kill the kernel.
-
-        Parameters:
-        -----------
-        kernel : Popen
-            An existing kernel process.
-        """
         self._kernel = kernel
+        self._xreq_address = (LOCALHOST, xrep)
+        self._sub_address = (LOCALHOST, pub)
+        # The rep channel is not fully working yet, but its base class makes
+        # sure the port is not 0. We set to -1 for now until the rep channel
+        # is fully working.
+        self._rep_address = (LOCALHOST, -1)
 
     @property
     def has_kernel(self):
         """Returns whether a kernel process has been specified for the kernel
         manager.
 
         A kernel process can be set via 'start_kernel' or 'set_kernel'.
         """
         return self._kernel is not None
 
     def kill_kernel(self):
         """ Kill the running kernel. """
-        if self._kernel:
+        if self._kernel is not None:
             self._kernel.kill()
             self._kernel = None
         else:
             raise RuntimeError("Cannot kill kernel. No kernel is running!")
 
     def signal_kernel(self, signum):
         """ Sends a signal to the kernel. """
-        if self._kernel:
+        if self._kernel is not None:
             self._kernel.send_signal(signum)
         else:
             raise RuntimeError("Cannot signal kernel. No kernel is running!")
 
+    @property
+    def is_alive(self):
+        """Is the kernel process still running?"""
+        if self._kernel is not None:
+            if self._kernel.poll() is None:
+                return True
+            else:
+                return False
+        else:
+            # We didn't start the kernel with this KernelManager so we don't
+            # know if it is running. We should use a heartbeat for this case.
+            return True
+
     #--------------------------------------------------------------------------
     # Channels used for communication with the kernel:
     #--------------------------------------------------------------------------
 
     @property
-    def sub_channel(self):
-        """Get the SUB socket channel object."""
-        if self._sub_channel is None:
-            self._sub_channel = self.sub_channel_class(self.context,
-                                                       self.session)
-        return self._sub_channel
-
-    @property
     def xreq_channel(self):
         """Get the REQ socket channel object to make requests of the kernel."""
         if self._xreq_channel is None:
             self._xreq_channel = self.xreq_channel_class(self.context, 
-                                                         self.session)
+                                                         self.session,
+                                                         self.xreq_address)
         return self._xreq_channel
 
     @property
+    def sub_channel(self):
+        """Get the SUB socket channel object."""
+        if self._sub_channel is None:
+            self._sub_channel = self.sub_channel_class(self.context,
+                                                       self.session,
+                                                       self.sub_address)
+        return self._sub_channel
+
+    @property
     def rep_channel(self):
         """Get the REP socket channel object to handle stdin (raw_input)."""
         if self._rep_channel is None:
             self._rep_channel = self.rep_channel_class(self.context, 
-                                                       self.session)
+                                                       self.session,
+                                                       self.rep_address)
         return self._rep_channel
 
-    #--------------------------------------------------------------------------
-    # Delegates for the Channel address attributes:
-    #--------------------------------------------------------------------------
-
-    def get_sub_address(self):
-        return self.sub_channel.address
-
-    def set_sub_address(self, address):
-        self.sub_channel.address = address
-
-    sub_address = property(get_sub_address, set_sub_address,
-                           doc="The address used by SUB socket channel.")
-
-    def get_xreq_address(self):
-        return self.xreq_channel.address
-
-    def set_xreq_address(self, address):
-        self.xreq_channel.address = address
-
-    xreq_address = property(get_xreq_address, set_xreq_address,
-                            doc="The address used by XREQ socket channel.")
+    @property
+    def xreq_address(self):
+        return self._xreq_address
     
-    def get_rep_address(self):
-        return self.rep_channel.address
+    @property
+    def sub_address(self):
+        return self._sub_address
 
-    def set_rep_address(self, address):
-        self.rep_channel.address = address
+    @property
+    def rep_address(self):
+        return self._rep_address
 
-    rep_address = property(get_rep_address, set_rep_address,
-                           doc="The address used by REP socket channel.")