actually send only one kernel_info request

store the Future for the initial request,
allowing subsequent requests to wait on the same pending reply.

Previously, any incoming requests that arrived while waiting for the first reply would send their own request.

IPython/html/services/kernels/handlers.py

@@ -103,8 +103,8 @@ class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
         km = self.kernel_manager
         kernel = km.get_kernel(self.kernel_id)
         try:
-            # check for cached value
-            kernel_info = kernel._kernel_info
+            # check for previous request
+            future = kernel._kernel_info_future
         except AttributeError:
             self.log.debug("Requesting kernel info from %s", self.kernel_id)
             # Create a kernel_info channel to query the kernel protocol version.
@@ -113,9 +113,12 @@ class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
                 self.kernel_info_channel = km.connect_shell(self.kernel_id)
             self.kernel_info_channel.on_recv(self._handle_kernel_info_reply)
             self.session.send(self.kernel_info_channel, "kernel_info_request")
+            # store the future on the kernel, so only one request is sent
+            kernel._kernel_info_future = self._kernel_info_future
         else:
-            # use cached value, don't resend request
-            self._finish_kernel_info(kernel_info)
+            if not future.done():
+                self.log.debug("Waiting for pending kernel_info request")
+            future.add_done_callback(lambda f: self._finish_kernel_info(f.result()))
         return self._kernel_info_future
     
     def _handle_kernel_info_reply(self, msg):
@@ -128,16 +131,14 @@ class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
             msg = self.session.deserialize(msg)
         except:
             self.log.error("Bad kernel_info reply", exc_info=True)
-            self._kernel_info_future.set_result(None)
+            self._kernel_info_future.set_result({})
             return
         else:
             info = msg['content']
             self.log.debug("Received kernel info: %s", info)
             if msg['msg_type'] != 'kernel_info_reply' or 'protocol_version' not in info:
                 self.log.error("Kernel info request failed, assuming current %s", info)
-            else:
-                kernel = self.kernel_manager.get_kernel(self.kernel_id)
-                kernel._kernel_info = info
+                info = {}
             self._finish_kernel_info(info)
         
         # close the kernel_info channel, we don't need it anymore
@@ -179,7 +180,7 @@ class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
             if future.done():
                 return
             self.log.warn("Timeout waiting for kernel_info reply from %s", self.kernel_id)
-            future.set_result(None)
+            future.set_result({})
         loop = IOLoop.current()
         loop.add_timeout(loop.time() + self.kernel_info_timeout, give_up)
         # actually wait for it