make Comm's publishing threadsafe

If a Comm tries to send a message from another thread,
schedule it to be called ASAP in the main thread
via IOLoop.add_callback

IPython/kernel/comm/comm.py

@@ -1,162 +1,169 b''
 """Base class for a Comm"""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import threading
 import uuid
 
+from zmq.eventloop.ioloop import IOLoop
+
 from IPython.config import LoggingConfigurable
 from IPython.kernel.zmq.kernelbase import Kernel
 
 from IPython.utils.jsonutil import json_clean
 from IPython.utils.traitlets import Instance, Unicode, Bytes, Bool, Dict, Any
 
 
 class Comm(LoggingConfigurable):
-    
+    """Class for communicating between a Frontend and a Kernel"""
     # If this is instantiated by a non-IPython kernel, shell will be None
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC',
                      allow_none=True)
     kernel = Instance('IPython.kernel.zmq.kernelbase.Kernel')
     def _kernel_default(self):
         if Kernel.initialized():
             return Kernel.instance()
     
     iopub_socket = Any()
     def _iopub_socket_default(self):
         return self.kernel.iopub_socket
     session = Instance('IPython.kernel.zmq.session.Session')
     def _session_default(self):
         if self.kernel is not None:
             return self.kernel.session
     
     target_name = Unicode('comm')
     target_module = Unicode(None, allow_none=True, help="""requirejs module from
         which to load comm target.""")
     
     topic = Bytes()
     def _topic_default(self):
         return ('comm-%s' % self.comm_id).encode('ascii')
     
     _open_data = Dict(help="data dict, if any, to be included in comm_open")
     _close_data = Dict(help="data dict, if any, to be included in comm_close")
     
     _msg_callback = Any()
     _close_callback = Any()
     
     _closed = Bool(True)
     comm_id = Unicode()
     def _comm_id_default(self):
         return uuid.uuid4().hex
     
     primary = Bool(True, help="Am I the primary or secondary Comm?")
     
     def __init__(self, target_name='', data=None, **kwargs):
         if target_name:
             kwargs['target_name'] = target_name
         super(Comm, self).__init__(**kwargs)
         if self.primary:
             # I am primary, open my peer.
             self.open(data)
         else:
             self._closed = False
     
     def _publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys):
         """Helper for sending a comm message on IOPub"""
+        if threading.current_thread().name != 'MainThread' and IOLoop.initialized():
+            # make sure we never send on a zmq socket outside the main IOLoop thread
+            IOLoop.instance().add_callback(lambda : self._publish_msg(msg_type, data, metadata, buffers, **keys))
+            return
         data = {} if data is None else data
         metadata = {} if metadata is None else metadata
         content = json_clean(dict(data=data, comm_id=self.comm_id, **keys))
         self.session.send(self.iopub_socket, msg_type,
             content,
             metadata=json_clean(metadata),
             parent=self.kernel._parent_header,
             ident=self.topic,
             buffers=buffers,
         )
     
     def __del__(self):
         """trigger close on gc"""
         self.close()
     
     # publishing messages
     
     def open(self, data=None, metadata=None, buffers=None):
         """Open the frontend-side version of this comm"""
         if data is None:
             data = self._open_data
         comm_manager = getattr(self.kernel, 'comm_manager', None)
         if comm_manager is None:
             raise RuntimeError("Comms cannot be opened without a kernel "
                         "and a comm_manager attached to that kernel.")
 
         comm_manager.register_comm(self)
         try:
             self._publish_msg('comm_open',
                               data=data, metadata=metadata, buffers=buffers,
                               target_name=self.target_name,
                               target_module=self.target_module,
                               )
             self._closed = False
         except:
             comm_manager.unregister_comm(self)
             raise
     
     def close(self, data=None, metadata=None, buffers=None):
         """Close the frontend-side version of this comm"""
         if self._closed:
             # only close once
             return
         self._closed = True
         if data is None:
             data = self._close_data
         self._publish_msg('comm_close',
             data=data, metadata=metadata, buffers=buffers,
         )
         self.kernel.comm_manager.unregister_comm(self)
     
     def send(self, data=None, metadata=None, buffers=None):
         """Send a message to the frontend-side version of this comm"""
         self._publish_msg('comm_msg',
             data=data, metadata=metadata, buffers=buffers,
         )
     
     # registering callbacks
     
     def on_close(self, callback):
         """Register a callback for comm_close
         
         Will be called with the `data` of the close message.
         
         Call `on_close(None)` to disable an existing callback.
         """
         self._close_callback = callback
     
     def on_msg(self, callback):
         """Register a callback for comm_msg
         
         Will be called with the `data` of any comm_msg messages.
         
         Call `on_msg(None)` to disable an existing callback.
         """
         self._msg_callback = callback
     
     # handling of incoming messages
     
     def handle_close(self, msg):
         """Handle a comm_close message"""
         self.log.debug("handle_close[%s](%s)", self.comm_id, msg)
         if self._close_callback:
             self._close_callback(msg)
     
     def handle_msg(self, msg):
         """Handle a comm_msg message"""
         self.log.debug("handle_msg[%s](%s)", self.comm_id, msg)
         if self._msg_callback:
             if self.shell:
                 self.shell.events.trigger('pre_execute')
             self._msg_callback(msg)
             if self.shell:
                 self.shell.events.trigger('post_execute')
 
 
 __all__ = ['Comm']