Handle kernel messages synchronously

A problem can happen when two messages come in for different
comms, where the second depends on the first (for example, the
first might be a message setting the state of a widget, and the
second triggering a view creation for the widget).  Since comm
message queues are independent of each other, the second message
could be executed before the first message.

This exposes a more fundamental assumption users are likely to
have that messages from python are processed synchronously.

Thanks to @dmadeka for reporting an error that led to discovering this issue.

IPython/html/static/services/kernels/comm.js

@@ -1,217 +1,219 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     'base/js/namespace',
     'jquery',
     'base/js/utils',
 ], function(IPython, $, utils) {
     "use strict";
 
     //-----------------------------------------------------------------------
     // CommManager class
     //-----------------------------------------------------------------------
     
     var CommManager = function (kernel) {
         this.comms = {};
         this.targets = {};
         if (kernel !== undefined) {
             this.init_kernel(kernel);
         }
     };
     
     CommManager.prototype.init_kernel = function (kernel) {
         /**
          * connect the kernel, and register message handlers
          */
         this.kernel = kernel;
         var msg_types = ['comm_open', 'comm_msg', 'comm_close'];
         for (var i = 0; i < msg_types.length; i++) {
             var msg_type = msg_types[i];
             kernel.register_iopub_handler(msg_type, $.proxy(this[msg_type], this));
         }
     };
     
     CommManager.prototype.new_comm = function (target_name, data, callbacks, metadata) {
         /**
          * Create a new Comm, register it, and open its Kernel-side counterpart
          * Mimics the auto-registration in `Comm.__init__` in the IPython Comm
          */
         var comm = new Comm(target_name);
         this.register_comm(comm);
         comm.open(data, callbacks, metadata);
         return comm;
     };
     
     CommManager.prototype.register_target = function (target_name, f) {
         /**
          * Register a target function for a given target name
          */
         this.targets[target_name] = f;
     };
     
     CommManager.prototype.unregister_target = function (target_name, f) {
         /**
          * Unregister a target function for a given target name
          */
         delete this.targets[target_name];
     };
     
     CommManager.prototype.register_comm = function (comm) {
         /**
          * Register a comm in the mapping
          */
         this.comms[comm.comm_id] = Promise.resolve(comm);
         comm.kernel = this.kernel;
         return comm.comm_id;
     };
     
     CommManager.prototype.unregister_comm = function (comm) {
         /**
          * Remove a comm from the mapping
          */
         delete this.comms[comm.comm_id];
     };
     
     // comm message handlers
     
     CommManager.prototype.comm_open = function (msg) {
         var content = msg.content;
         var that = this;
         var comm_id = content.comm_id;
 
         this.comms[comm_id] = utils.load_class(content.target_name, content.target_module, 
             this.targets).then(function(target) {
                 var comm = new Comm(content.target_name, comm_id);
                 comm.kernel = that.kernel;
                 try {
                     var response = target(comm, msg);
                 } catch (e) {
                     comm.close();
                     that.unregister_comm(comm);
                     var wrapped_error = new utils.WrappedError("Exception opening new comm", e);
                     console.error(wrapped_error);
                     return Promise.reject(wrapped_error);
                 }
                 // Regardless of the target return value, we need to
                 // then return the comm
                 return Promise.resolve(response).then(function() {return comm;});
             }, utils.reject('Could not open comm', true));
         return this.comms[comm_id];
     };
     
     CommManager.prototype.comm_close = function(msg) {
         var content = msg.content;
         if (this.comms[content.comm_id] === undefined) {
             console.error('Comm promise not found for comm id ' + content.comm_id);
             return;
         }
         var that = this;
         this.comms[content.comm_id] = this.comms[content.comm_id].then(function(comm) {
             that.unregister_comm(comm);
             try {
                 comm.handle_close(msg);
             } catch (e) {
                 console.log("Exception closing comm: ", e, e.stack, msg);
             }
             // don't return a comm, so that further .then() functions
             // get an undefined comm input
         });
+        return this.comms[content.comm_id];
     };
     
     CommManager.prototype.comm_msg = function(msg) {
         var content = msg.content;
         if (this.comms[content.comm_id] === undefined) {
             console.error('Comm promise not found for comm id ' + content.comm_id);
             return;
         }
 
         this.comms[content.comm_id] = this.comms[content.comm_id].then(function(comm) {
             try {
                 comm.handle_msg(msg);
             } catch (e) {
                 console.log("Exception handling comm msg: ", e, e.stack, msg);
             }
             return comm;
         });
+        return this.comms[content.comm_id];
     };
     
     //-----------------------------------------------------------------------
     // Comm base class
     //-----------------------------------------------------------------------
     
     var Comm = function (target_name, comm_id) {
         this.target_name = target_name;
         this.comm_id = comm_id || utils.uuid();
         this._msg_callback = this._close_callback = null;
     };
     
     // methods for sending messages
     Comm.prototype.open = function (data, callbacks, metadata) {
         var content = {
             comm_id : this.comm_id,
             target_name : this.target_name,
             data : data || {},
         };
         return this.kernel.send_shell_message("comm_open", content, callbacks, metadata);
     };
     
     Comm.prototype.send = function (data, callbacks, metadata, buffers) {
         var content = {
             comm_id : this.comm_id,
             data : data || {},
         };
         return this.kernel.send_shell_message("comm_msg", content, callbacks, metadata, buffers);
     };
     
     Comm.prototype.close = function (data, callbacks, metadata) {
         var content = {
             comm_id : this.comm_id,
             data : data || {},
         };
         return this.kernel.send_shell_message("comm_close", content, callbacks, metadata);
     };
     
     // methods for registering callbacks for incoming messages
     Comm.prototype._register_callback = function (key, callback) {
         this['_' + key + '_callback'] = callback;
     };
     
     Comm.prototype.on_msg = function (callback) {
         this._register_callback('msg', callback);
     };
     
     Comm.prototype.on_close = function (callback) {
         this._register_callback('close', callback);
     };
     
     // methods for handling incoming messages
     
     Comm.prototype._callback = function (key, msg) {
         var callback = this['_' + key + '_callback'];
         if (callback) {
             try {
                 callback(msg);
             } catch (e) {
                 console.log("Exception in Comm callback", e, e.stack, msg);
             }
         }
     };
     
     Comm.prototype.handle_msg = function (msg) {
         this._callback('msg', msg);
     };
     
     Comm.prototype.handle_close = function (msg) {
         this._callback('close', msg);
     };
     
     // For backwards compatability.
     IPython.CommManager = CommManager;
     IPython.Comm = Comm;
 
     return {
         'CommManager': CommManager,
         'Comm': Comm
     };
 });

IPython/html/static/services/kernels/kernel.js

@@ -1,1056 +1,1064 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     'base/js/namespace',
     'jquery',
     'base/js/utils',
     './comm',
     './serialize',
     'widgets/js/init'
 ], function(IPython, $, utils, comm, serialize, widgetmanager) {
     "use strict";
 
     /**
      * A Kernel class to communicate with the Python kernel. This
      * should generally not be constructed directly, but be created
      * by.  the `Session` object. Once created, this object should be
      * used to communicate with the kernel.
      * 
      * @class Kernel
      * @param {string} kernel_service_url - the URL to access the kernel REST api
      * @param {string} ws_url - the websockets URL
      * @param {Notebook} notebook - notebook object
      * @param {string} name - the kernel type (e.g. python3)
      */
     var Kernel = function (kernel_service_url, ws_url, notebook, name) {
         this.events = notebook.events;
 
         this.id = null;
         this.name = name;
         this.ws = null;
 
         this.kernel_service_url = kernel_service_url;
         this.kernel_url = null;
         this.ws_url = ws_url || IPython.utils.get_body_data("wsUrl");
         if (!this.ws_url) {
             // trailing 's' in https will become wss for secure web sockets
             this.ws_url = location.protocol.replace('http', 'ws') + "//" + location.host;
         }
 
         this.username = "username";
         this.session_id = utils.uuid();
         this._msg_callbacks = {};
         this._msg_queue = Promise.resolve();
         this.info_reply = {}; // kernel_info_reply stored here after starting
 
         if (typeof(WebSocket) !== 'undefined') {
             this.WebSocket = WebSocket;
         } else if (typeof(MozWebSocket) !== 'undefined') {
             this.WebSocket = MozWebSocket;
         } else {
             alert('Your browser does not have WebSocket support, please try Chrome, Safari or Firefox ≥ 6. Firefox 4 and 5 are also supported by you have to enable WebSockets in about:config.');
         }
         
         this.bind_events();
         this.init_iopub_handlers();
         this.comm_manager = new comm.CommManager(this);
         this.widget_manager = new widgetmanager.WidgetManager(this.comm_manager, notebook);
         
         this.last_msg_id = null;
         this.last_msg_callbacks = {};
 
         this._autorestart_attempt = 0;
         this._reconnect_attempt = 0;
         this.reconnect_limit = 7;
     };
 
     /**
      * @function _get_msg
      */
     Kernel.prototype._get_msg = function (msg_type, content, metadata, buffers) {
         var msg = {
             header : {
                 msg_id : utils.uuid(),
                 username : this.username,
                 session : this.session_id,
                 msg_type : msg_type,
                 version : "5.0"
             },
             metadata : metadata || {},
             content : content,
             buffers : buffers || [],
             parent_header : {}
         };
         return msg;
     };
 
     /**
      * @function bind_events
      */
     Kernel.prototype.bind_events = function () {
         var that = this;
         this.events.on('send_input_reply.Kernel', function(evt, data) { 
             that.send_input_reply(data);
         });
 
         var record_status = function (evt, info) {
             console.log('Kernel: ' + evt.type + ' (' + info.kernel.id + ')');
         };
 
         this.events.on('kernel_created.Kernel', record_status);
         this.events.on('kernel_reconnecting.Kernel', record_status);
         this.events.on('kernel_connected.Kernel', record_status);
         this.events.on('kernel_starting.Kernel', record_status);
         this.events.on('kernel_restarting.Kernel', record_status);
         this.events.on('kernel_autorestarting.Kernel', record_status);
         this.events.on('kernel_interrupting.Kernel', record_status);
         this.events.on('kernel_disconnected.Kernel', record_status);
         // these are commented out because they are triggered a lot, but can
         // be uncommented for debugging purposes
         //this.events.on('kernel_idle.Kernel', record_status);
         //this.events.on('kernel_busy.Kernel', record_status);
         this.events.on('kernel_ready.Kernel', record_status);
         this.events.on('kernel_killed.Kernel', record_status);
         this.events.on('kernel_dead.Kernel', record_status);
 
         this.events.on('kernel_ready.Kernel', function () {
             that._autorestart_attempt = 0;
         });
         this.events.on('kernel_connected.Kernel', function () {
             that._reconnect_attempt = 0;
         });
     };
 
     /**
      * Initialize the iopub handlers.
      *
      * @function init_iopub_handlers
      */
     Kernel.prototype.init_iopub_handlers = function () {
         var output_msg_types = ['stream', 'display_data', 'execute_result', 'error'];
         this._iopub_handlers = {};
         this.register_iopub_handler('status', $.proxy(this._handle_status_message, this));
         this.register_iopub_handler('clear_output', $.proxy(this._handle_clear_output, this));
         this.register_iopub_handler('execute_input', $.proxy(this._handle_input_message, this));
         
         for (var i=0; i < output_msg_types.length; i++) {
             this.register_iopub_handler(output_msg_types[i], $.proxy(this._handle_output_message, this));
         }
     };
 
     /**
      * GET /api/kernels
      *
      * Get the list of running kernels.
      *
      * @function list
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.list = function (success, error) {
         $.ajax(this.kernel_service_url, {
             processData: false,
             cache: false,
             type: "GET",
             dataType: "json",
             success: success,
             error: this._on_error(error)
         });
     };
 
     /**
      * POST /api/kernels
      *
      * Start a new kernel.
      *
      * In general this shouldn't be used -- the kernel should be
      * started through the session API. If you use this function and
      * are also using the session API then your session and kernel
      * WILL be out of sync!
      *
      * @function start
      * @param {params} [Object] - parameters to include in the query string
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.start = function (params, success, error) {
         var url = this.kernel_service_url;
         var qs = $.param(params || {}); // query string for sage math stuff
         if (qs !== "") {
             url = url + "?" + qs;
         }
 
         this.events.trigger('kernel_starting.Kernel', {kernel: this});
         var that = this;
         var on_success = function (data, status, xhr) {
             that.events.trigger('kernel_created.Kernel', {kernel: that});
             that._kernel_created(data);
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             data: JSON.stringify({name: this.name}),
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(error)
         });
 
         return url;
     };
 
     /**
      * GET /api/kernels/[:kernel_id]
      *
      * Get information about the kernel.
      *
      * @function get_info
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.get_info = function (success, error) {
         $.ajax(this.kernel_url, {
             processData: false,
             cache: false,
             type: "GET",
             dataType: "json",
             success: this._on_success(success),
             error: this._on_error(error)
         });
     };
 
     /**
      * DELETE /api/kernels/[:kernel_id]
      *
      * Shutdown the kernel.
      *
      * If you are also using sessions, then this function shoul NOT be
      * used. Instead, use Session.delete. Otherwise, the session and
      * kernel WILL be out of sync.
      *
      * @function kill
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.kill = function (success, error) {
         this.events.trigger('kernel_killed.Kernel', {kernel: this});
         this._kernel_dead();
         $.ajax(this.kernel_url, {
             processData: false,
             cache: false,
             type: "DELETE",
             dataType: "json",
             success: this._on_success(success),
             error: this._on_error(error)
         });
     };
 
     /**
      * POST /api/kernels/[:kernel_id]/interrupt
      *
      * Interrupt the kernel.
      *
      * @function interrupt
      * @param {function} [success] - function executed on ajax success
      * @param {function} [error] - functon executed on ajax error
      */
     Kernel.prototype.interrupt = function (success, error) {
         this.events.trigger('kernel_interrupting.Kernel', {kernel: this});
 
         var that = this;
         var on_success = function (data, status, xhr) {
             /**
              * get kernel info so we know what state the kernel is in
              */
             that.kernel_info();
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         var url = utils.url_join_encode(this.kernel_url, 'interrupt');
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(error)
         });
     };
 
     Kernel.prototype.restart = function (success, error) {
         /**
          * POST /api/kernels/[:kernel_id]/restart
          *
          * Restart the kernel.
          *
          * @function interrupt
          * @param {function} [success] - function executed on ajax success
          * @param {function} [error] - functon executed on ajax error
          */
         this.events.trigger('kernel_restarting.Kernel', {kernel: this});
         this.stop_channels();
 
         var that = this;
         var on_success = function (data, status, xhr) {
             that.events.trigger('kernel_created.Kernel', {kernel: that});
             that._kernel_created(data);
             if (success) {
                 success(data, status, xhr);
             }
         };
 
         var on_error = function (xhr, status, err) {
             that.events.trigger('kernel_dead.Kernel', {kernel: that});
             that._kernel_dead();
             if (error) {
                 error(xhr, status, err);
             }
         };
 
         var url = utils.url_join_encode(this.kernel_url, 'restart');
         $.ajax(url, {
             processData: false,
             cache: false,
             type: "POST",
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(on_error)
         });
     };
 
     Kernel.prototype.reconnect = function () {
         /**
          * Reconnect to a disconnected kernel. This is not actually a
          * standard HTTP request, but useful function nonetheless for
          * reconnecting to the kernel if the connection is somehow lost.
          *
          * @function reconnect
          */
         if (this.is_connected()) {
             return;
         }
         this._reconnect_attempt = this._reconnect_attempt + 1;
         this.events.trigger('kernel_reconnecting.Kernel', {
             kernel: this,
             attempt: this._reconnect_attempt,
         });
         this.start_channels();
     };
 
     Kernel.prototype._on_success = function (success) {
         /**
          * Handle a successful AJAX request by updating the kernel id and
          * name from the response, and then optionally calling a provided
          * callback.
          *
          * @function _on_success
          * @param {function} success - callback
          */
         var that = this;
         return function (data, status, xhr) {
             if (data) {
                 that.id = data.id;
                 that.name = data.name;
             }
             that.kernel_url = utils.url_join_encode(that.kernel_service_url, that.id);
             if (success) {
                 success(data, status, xhr);
             }
         };
     };
 
     Kernel.prototype._on_error = function (error) {
         /**
          * Handle a failed AJAX request by logging the error message, and
          * then optionally calling a provided callback.
          *
          * @function _on_error
          * @param {function} error - callback
          */
         return function (xhr, status, err) {
             utils.log_ajax_error(xhr, status, err);
             if (error) {
                 error(xhr, status, err);
             }
         };
     };
 
     Kernel.prototype._kernel_created = function (data) {
         /**
          * Perform necessary tasks once the kernel has been started,
          * including actually connecting to the kernel.
          *
          * @function _kernel_created
          * @param {Object} data - information about the kernel including id
          */
         this.id = data.id;
         this.kernel_url = utils.url_join_encode(this.kernel_service_url, this.id);
         this.start_channels();
     };
 
     Kernel.prototype._kernel_connected = function () {
         /**
          * Perform necessary tasks once the connection to the kernel has
          * been established. This includes requesting information about
          * the kernel.
          *
          * @function _kernel_connected
          */
         this.events.trigger('kernel_connected.Kernel', {kernel: this});
         // get kernel info so we know what state the kernel is in
         var that = this;
         this.kernel_info(function (reply) {
             that.info_reply = reply.content;
             that.events.trigger('kernel_ready.Kernel', {kernel: that});
         });
     };
 
     Kernel.prototype._kernel_dead = function () {
         /**
          * Perform necessary tasks after the kernel has died. This closing
          * communication channels to the kernel if they are still somehow
          * open.
          *
          * @function _kernel_dead
          */
         this.stop_channels();
     };
 
     Kernel.prototype.start_channels = function () {
         /**
          * Start the websocket channels.
          * Will stop and restart them if they already exist.
          *
          * @function start_channels
          */
         var that = this;
         this.stop_channels();
         var ws_host_url = this.ws_url + this.kernel_url;
 
         console.log("Starting WebSockets:", ws_host_url);
         
         this.ws = new this.WebSocket([
                 that.ws_url,
                 utils.url_join_encode(that.kernel_url, 'channels'),
                 "?session_id=" + that.session_id
             ].join('')
         );
         
         var already_called_onclose = false; // only alert once
         var ws_closed_early = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             if ( ! evt.wasClean ){
                 // If the websocket was closed early, that could mean
                 // that the kernel is actually dead. Try getting
                 // information about the kernel from the API call --
                 // if that fails, then assume the kernel is dead,
                 // otherwise just follow the typical websocket closed
                 // protocol.
                 that.get_info(function () {
                     that._ws_closed(ws_host_url, false);
                 }, function () {
                     that.events.trigger('kernel_dead.Kernel', {kernel: that});
                     that._kernel_dead();
                 });
             }
         };
         var ws_closed_late = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             if ( ! evt.wasClean ){
                 that._ws_closed(ws_host_url, false);
             }
         };
         var ws_error = function(evt){
             if (already_called_onclose){
                 return;
             }
             already_called_onclose = true;
             that._ws_closed(ws_host_url, true);
         };
 
         this.ws.onopen = $.proxy(this._ws_opened, this);
         this.ws.onclose = ws_closed_early;
         this.ws.onerror = ws_error;
         // switch from early-close to late-close message after 1s
         setTimeout(function() {
             if (that.ws !== null) {
                 that.ws.onclose = ws_closed_late;
             }
         }, 1000);
         this.ws.onmessage = $.proxy(this._handle_ws_message, this);
     };
 
     Kernel.prototype._ws_opened = function (evt) {
         /**
          * Handle a websocket entering the open state,
          * signaling that the kernel is connected when websocket is open.
          *
          * @function _ws_opened
          */
         if (this.is_connected()) {
             // all events ready, trigger started event.
             this._kernel_connected();
         }
     };
 
     Kernel.prototype._ws_closed = function(ws_url, error) {
         /**
          * Handle a websocket entering the closed state.  If the websocket
          * was not closed due to an error, try to reconnect to the kernel.
          *
          * @function _ws_closed
          * @param {string} ws_url - the websocket url
          * @param {bool} error - whether the connection was closed due to an error
          */
         this.stop_channels();
 
         this.events.trigger('kernel_disconnected.Kernel', {kernel: this});
         if (error) {
             console.log('WebSocket connection failed: ', ws_url);
             this.events.trigger('kernel_connection_failed.Kernel', {kernel: this, ws_url: ws_url, attempt: this._reconnect_attempt});
         }
         this._schedule_reconnect();
     };
     
     Kernel.prototype._schedule_reconnect = function () {
         /**
          * function to call when kernel connection is lost
          * schedules reconnect, or fires 'connection_dead' if reconnect limit is hit
          */
         if (this._reconnect_attempt < this.reconnect_limit) {
             var timeout = Math.pow(2, this._reconnect_attempt);
             console.log("Connection lost, reconnecting in " + timeout + " seconds.");
             setTimeout($.proxy(this.reconnect, this), 1e3 * timeout);
         } else {
             this.events.trigger('kernel_connection_dead.Kernel', {
                 kernel: this,
                 reconnect_attempt: this._reconnect_attempt,
             });
             console.log("Failed to reconnect, giving up.");
         }
     };
     
     Kernel.prototype.stop_channels = function () {
         /**
          * Close the websocket. After successful close, the value
          * in `this.ws` will be null.
          *
          * @function stop_channels
          */
         var that = this;
         var close = function () {
             if (that.ws && that.ws.readyState === WebSocket.CLOSED) {
                 that.ws = null;
             }
         };
         if (this.ws !== null) {
             if (this.ws.readyState === WebSocket.OPEN) {
                 this.ws.onclose = close;
                 this.ws.close();
             } else {
                 close();
             }
         }
     };
 
     Kernel.prototype.is_connected = function () {
         /**
          * Check whether there is a connection to the kernel. This
          * function only returns true if websocket has been
          * created and has a state of WebSocket.OPEN.
          *
          * @function is_connected
          * @returns {bool} - whether there is a connection
          */
         // if any channel is not ready, then we're not connected
         if (this.ws === null) {
             return false;
         }
         if (this.ws.readyState !== WebSocket.OPEN) {
             return false;
         }
         return true;
     };
 
     Kernel.prototype.is_fully_disconnected = function () {
         /**
          * Check whether the connection to the kernel has been completely
          * severed. This function only returns true if all channel objects
          * are null.
          *
          * @function is_fully_disconnected
          * @returns {bool} - whether the kernel is fully disconnected
          */
         return (this.ws === null);
     };
     
     Kernel.prototype.send_shell_message = function (msg_type, content, callbacks, metadata, buffers) {
         /**
          * Send a message on the Kernel's shell channel
          *
          * @function send_shell_message
          */
         if (!this.is_connected()) {
             throw new Error("kernel is not connected");
         }
         var msg = this._get_msg(msg_type, content, metadata, buffers);
         msg.channel = 'shell';
         this.ws.send(serialize.serialize(msg));
         this.set_callbacks_for_msg(msg.header.msg_id, callbacks);
         return msg.header.msg_id;
     };
 
     Kernel.prototype.kernel_info = function (callback) {
         /**
          * Get kernel info
          *
          * @function kernel_info
          * @param callback {function}
          *
          * When calling this method, pass a callback function that expects one argument.
          * The callback will be passed the complete `kernel_info_reply` message documented
          * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#kernel-info)
          */
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         return this.send_shell_message("kernel_info_request", {}, callbacks);
     };
 
     Kernel.prototype.inspect = function (code, cursor_pos, callback) {
         /**
          * Get info on an object
          *
          * When calling this method, pass a callback function that expects one argument.
          * The callback will be passed the complete `inspect_reply` message documented
          * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#object-information)
          *
          * @function inspect
          * @param code {string}
          * @param cursor_pos {integer}
          * @param callback {function}
          */
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         
         var content = {
             code : code,
             cursor_pos : cursor_pos,
             detail_level : 0
         };
         return this.send_shell_message("inspect_request", content, callbacks);
     };
 
     Kernel.prototype.execute = function (code, callbacks, options) {
         /**
          * Execute given code into kernel, and pass result to callback.
          *
          * @async
          * @function execute
          * @param {string} code
          * @param [callbacks] {Object} With the following keys (all optional)
          *      @param callbacks.shell.reply {function}
          *      @param callbacks.shell.payload.[payload_name] {function}
          *      @param callbacks.iopub.output {function}
          *      @param callbacks.iopub.clear_output {function}
          *      @param callbacks.input {function}
          * @param {object} [options]
          *      @param [options.silent=false] {Boolean}
          *      @param [options.user_expressions=empty_dict] {Dict}
          *      @param [options.allow_stdin=false] {Boolean} true|false
          *
          * @example
          *
          * The options object should contain the options for the execute
          * call. Its default values are:
          *
          *      options = {
          *        silent : true,
          *        user_expressions : {},
          *        allow_stdin : false
          *      }
          *
          * When calling this method pass a callbacks structure of the
          * form:
          *
          *      callbacks = {
          *       shell : {
          *         reply : execute_reply_callback,
          *         payload : {
          *           set_next_input : set_next_input_callback,
          *         }
          *       },
          *       iopub : {
          *         output : output_callback,
          *         clear_output : clear_output_callback,
          *       },
          *       input : raw_input_callback
          *      }
          *
          * Each callback will be passed the entire message as a single
          * arugment.  Payload handlers will be passed the corresponding
          * payload and the execute_reply message.
          */
         var content = {
             code : code,
             silent : true,
             store_history : false,
             user_expressions : {},
             allow_stdin : false
         };
         callbacks = callbacks || {};
         if (callbacks.input !== undefined) {
             content.allow_stdin = true;
         }
         $.extend(true, content, options);
         this.events.trigger('execution_request.Kernel', {kernel: this, content: content});
         return this.send_shell_message("execute_request", content, callbacks);
     };
 
     /**
      * When calling this method, pass a function to be called with the
      * `complete_reply` message as its only argument when it arrives.
      *
      * `complete_reply` is documented
      * [here](http://ipython.org/ipython-doc/dev/development/messaging.html#complete)
      *
      * @function complete
      * @param code {string}
      * @param cursor_pos {integer}
      * @param callback {function}
      */
     Kernel.prototype.complete = function (code, cursor_pos, callback) {
         var callbacks;
         if (callback) {
             callbacks = { shell : { reply : callback } };
         }
         var content = {
             code : code,
             cursor_pos : cursor_pos
         };
         return this.send_shell_message("complete_request", content, callbacks);
     };
 
     /**
      * @function send_input_reply
      */
     Kernel.prototype.send_input_reply = function (input) {
         if (!this.is_connected()) {
             throw new Error("kernel is not connected");
         }
         var content = {
             value : input
         };
         this.events.trigger('input_reply.Kernel', {kernel: this, content: content});
         var msg = this._get_msg("input_reply", content);
         msg.channel = 'stdin';
         this.ws.send(serialize.serialize(msg));
         return msg.header.msg_id;
     };
 
     /**
      * @function register_iopub_handler
      */
     Kernel.prototype.register_iopub_handler = function (msg_type, callback) {
         this._iopub_handlers[msg_type] = callback;
     };
 
     /**
      * Get the iopub handler for a specific message type.
      *
      * @function get_iopub_handler
      */
     Kernel.prototype.get_iopub_handler = function (msg_type) {
         return this._iopub_handlers[msg_type];
     };
 
     /**
      * Get callbacks for a specific message.
      *
      * @function get_callbacks_for_msg
      */
     Kernel.prototype.get_callbacks_for_msg = function (msg_id) {
         if (msg_id == this.last_msg_id) {
             return this.last_msg_callbacks;
         } else {
             return this._msg_callbacks[msg_id];
         }
     };
 
     /**
      * Clear callbacks for a specific message.
      *
      * @function clear_callbacks_for_msg
      */
     Kernel.prototype.clear_callbacks_for_msg = function (msg_id) {
         if (this._msg_callbacks[msg_id] !== undefined ) {
             delete this._msg_callbacks[msg_id];
         }
     };
     
     /**
      * @function _finish_shell
      */
     Kernel.prototype._finish_shell = function (msg_id) {
         var callbacks = this._msg_callbacks[msg_id];
         if (callbacks !== undefined) {
             callbacks.shell_done = true;
             if (callbacks.iopub_done) {
                 this.clear_callbacks_for_msg(msg_id);
             }
         }
     };
 
     /**
      * @function _finish_iopub
      */
     Kernel.prototype._finish_iopub = function (msg_id) {
         var callbacks = this._msg_callbacks[msg_id];
         if (callbacks !== undefined) {
             callbacks.iopub_done = true;
             if (callbacks.shell_done) {
                 this.clear_callbacks_for_msg(msg_id);
             }
         }
     };
     
     /**
      * Set callbacks for a particular message.
      * Callbacks should be a struct of the following form:
      * shell : {
      * 
      * }
      *
      * @function set_callbacks_for_msg
      */
     Kernel.prototype.set_callbacks_for_msg = function (msg_id, callbacks) {
         this.last_msg_id = msg_id;
         if (callbacks) {
             // shallow-copy mapping, because we will modify it at the top level
             var cbcopy = this._msg_callbacks[msg_id] = this.last_msg_callbacks = {};
             cbcopy.shell = callbacks.shell;
             cbcopy.iopub = callbacks.iopub;
             cbcopy.input = callbacks.input;
             cbcopy.shell_done = (!callbacks.shell);
             cbcopy.iopub_done = (!callbacks.iopub);
         } else {
             this.last_msg_callbacks = {};
         }
     };
     
     Kernel.prototype._handle_ws_message = function (e) {
+        var that = this;
         this._msg_queue = this._msg_queue.then(function() {
             return serialize.deserialize(e.data);
-        }).then($.proxy(this._finish_ws_message, this))
+        }).then(function(msg) {return that._finish_ws_message(msg);})
         .catch(utils.reject("Couldn't process kernel message", true));
     };
 
     Kernel.prototype._finish_ws_message = function (msg) {
         switch (msg.channel) {
             case 'shell':
-                this._handle_shell_reply(msg);
+                return this._handle_shell_reply(msg);
                 break;
             case 'iopub':
-                this._handle_iopub_message(msg);
+                return this._handle_iopub_message(msg);
                 break;
             case 'stdin':
-                this._handle_input_request(msg);
+                return this._handle_input_request(msg);
                 break;
             default:
                 console.error("unrecognized message channel", msg.channel, msg);
         }
     };
     
     Kernel.prototype._handle_shell_reply = function (reply) {
         this.events.trigger('shell_reply.Kernel', {kernel: this, reply:reply});
+        var that = this;
         var content = reply.content;
         var metadata = reply.metadata;
         var parent_id = reply.parent_header.msg_id;
         var callbacks = this.get_callbacks_for_msg(parent_id);
+        var promise = Promise.resolve();
         if (!callbacks || !callbacks.shell) {
             return;
         }
         var shell_callbacks = callbacks.shell;
         
         // signal that shell callbacks are done
         this._finish_shell(parent_id);
         
         if (shell_callbacks.reply !== undefined) {
-            shell_callbacks.reply(reply);
+            promise = promise.then(function() {return shell_callbacks.reply(reply)});
         }
         if (content.payload && shell_callbacks.payload) {
-            this._handle_payloads(content.payload, shell_callbacks.payload, reply);
+            promise = promise.then(function() {
+                return that._handle_payloads(content.payload, shell_callbacks.payload, reply);
+            });
         }
+        return promise;
     };
 
     /**
      * @function _handle_payloads
      */
     Kernel.prototype._handle_payloads = function (payloads, payload_callbacks, msg) {
+        var promise = [];
         var l = payloads.length;
         // Payloads are handled by triggering events because we don't want the Kernel
         // to depend on the Notebook or Pager classes.
         for (var i=0; i<l; i++) {
             var payload = payloads[i];
             var callback = payload_callbacks[payload.source];
             if (callback) {
-                callback(payload, msg);
+                promise.push(callback(payload, msg));
             }
         }
+        return Promise.all(promise);
     };
 
     /**
      * @function _handle_status_message
      */
     Kernel.prototype._handle_status_message = function (msg) {
         var execution_state = msg.content.execution_state;
         var parent_id = msg.parent_header.msg_id;
         
         // dispatch status msg callbacks, if any
         var callbacks = this.get_callbacks_for_msg(parent_id);
         if (callbacks && callbacks.iopub && callbacks.iopub.status) {
             try {
                 callbacks.iopub.status(msg);
             } catch (e) {
                 console.log("Exception in status msg handler", e, e.stack);
             }
         }
         
         if (execution_state === 'busy') {
             this.events.trigger('kernel_busy.Kernel', {kernel: this});
 
         } else if (execution_state === 'idle') {
             // signal that iopub callbacks are (probably) done
             // async output may still arrive,
             // but only for the most recent request
             this._finish_iopub(parent_id);
             
             // trigger status_idle event
             this.events.trigger('kernel_idle.Kernel', {kernel: this});
 
         } else if (execution_state === 'starting') {
             this.events.trigger('kernel_starting.Kernel', {kernel: this});
             var that = this;
             this.kernel_info(function (reply) {
                 that.info_reply = reply.content;
                 that.events.trigger('kernel_ready.Kernel', {kernel: that});
             });
 
         } else if (execution_state === 'restarting') {
             // autorestarting is distinct from restarting,
             // in that it means the kernel died and the server is restarting it.
             // kernel_restarting sets the notification widget,
             // autorestart shows the more prominent dialog.
             this._autorestart_attempt = this._autorestart_attempt + 1;
             this.events.trigger('kernel_restarting.Kernel', {kernel: this});
             this.events.trigger('kernel_autorestarting.Kernel', {kernel: this, attempt: this._autorestart_attempt});
 
         } else if (execution_state === 'dead') {
             this.events.trigger('kernel_dead.Kernel', {kernel: this});
             this._kernel_dead();
         }
     };
     
     /**
      * Handle clear_output message
      *
      * @function _handle_clear_output
      */
     Kernel.prototype._handle_clear_output = function (msg) {
         var callbacks = this.get_callbacks_for_msg(msg.parent_header.msg_id);
         if (!callbacks || !callbacks.iopub) {
             return;
         }
         var callback = callbacks.iopub.clear_output;
         if (callback) {
             callback(msg);
         }
     };
 
     /**
      * handle an output message (execute_result, display_data, etc.)
      *
      * @function _handle_output_message
      */
     Kernel.prototype._handle_output_message = function (msg) {
         var callbacks = this.get_callbacks_for_msg(msg.parent_header.msg_id);
         if (!callbacks || !callbacks.iopub) {
             // The message came from another client. Let the UI decide what to
             // do with it.
             this.events.trigger('received_unsolicited_message.Kernel', msg);
             return;
         }
         var callback = callbacks.iopub.output;
         if (callback) {
             callback(msg);
         }
     };
 
     /**
      * Handle an input message (execute_input).
      *
      * @function _handle_input message
      */
     Kernel.prototype._handle_input_message = function (msg) {
         var callbacks = this.get_callbacks_for_msg(msg.parent_header.msg_id);
         if (!callbacks) {
             // The message came from another client. Let the UI decide what to
             // do with it.
             this.events.trigger('received_unsolicited_message.Kernel', msg);
         }
     };
 
     /**
      * Dispatch IOPub messages to respective handlers. Each message
      * type should have a handler.
      *
      * @function _handle_iopub_message
      */
     Kernel.prototype._handle_iopub_message = function (msg) {
         var handler = this.get_iopub_handler(msg.header.msg_type);
         if (handler !== undefined) {
-            handler(msg);
+            return handler(msg);
         }
     };
 
     /**
      * @function _handle_input_request
      */
     Kernel.prototype._handle_input_request = function (request) {
         var header = request.header;
         var content = request.content;
         var metadata = request.metadata;
         var msg_type = header.msg_type;
         if (msg_type !== 'input_request') {
             console.log("Invalid input request!", request);
             return;
         }
         var callbacks = this.get_callbacks_for_msg(request.parent_header.msg_id);
         if (callbacks) {
             if (callbacks.input) {
                 callbacks.input(request);
             }
         }
     };
 
     // Backwards compatability.
     IPython.Kernel = Kernel;
 
     return {'Kernel': Kernel};
 });