attempt with locks

Author: Carreau

ipykernel/kernelbase.py

@@ -23,6 +23,7 @@
 import zmq
 from tornado import ioloop
 from tornado import gen
+from tornado.locks import Semaphore
 from zmq.eventloop.zmqstream import ZMQStream
 
 from traitlets.config.configurable import SingletonConfigurable
@@ -38,6 +39,13 @@
 
 from ._version import kernel_protocol_version
 
+from collections import defaultdict
+
+# shell handlers are now coroutine (for async await code), 
+# so we may not want to consume all the message and block while it yields
+_msg_locks = defaultdict(Semaphore)
+
+
 class Kernel(SingletonConfigurable):
 
     #---------------------------------------------------------------------------
@@ -233,7 +241,9 @@ def dispatch_shell(self, stream, msg):
             self.log.debug("%s: %s", msg_type, msg)
             self.pre_handler_hook()
             try:
-                yield gen.maybe_future(handler(stream, idents, msg))
+                lock = _msg_locks[msg_type]
+                with (yield lock.acquire()):
+                    yield gen.maybe_future(handler(stream, idents, msg))
             except Exception:
                 self.log.error("Exception in message handler:", exc_info=True)
             finally:
@@ -376,7 +386,6 @@ def finish_metadata(self, parent, metadata, reply_content):
     @gen.coroutine
     def execute_request(self, stream, ident, parent):
         """handle an execute_request"""
-
         try:
             content = parent[u'content']
             code = py3compat.cast_unicode_py2(content[u'code'])