fix for tornado 6, backport of jupyter/notebook#4449

maartenbreddels · maartenbreddels · commit 0726b73ee90a · 2019-03-07T11:15:29.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -27,7 +27,7 @@ before_install:
       fi
 
 install:
-    - pip install --pre .[test]
+    - pip install --pre .[test] $EXTRA_PIP
     - wget https://github.com/jgm/pandoc/releases/download/1.19.1/pandoc-1.19.1-1-amd64.deb && sudo dpkg -i pandoc-1.19.1-1-amd64.deb
 
 
@@ -69,6 +69,10 @@ matrix:
           dist: xenial  # required for Python >= 3.7 (travis-ci/travis-ci#9069)
         - python: 3.6
           env: GROUP=docs
+        - python: 3.6  # extra test for older tornados
+          env:
+          - GROUP=python
+          - EXTRA_PIP="tornado<5"
 
 after_success:
     - codecov
diff --git a/jupyter_server/base/zmqhandlers.py b/jupyter_server/base/zmqhandlers.py
@@ -281,7 +281,8 @@ def get(self, *args, **kwargs):
         # assign and yield in two step to avoid tornado 3 issues
         res = self.pre_get()
         yield gen.maybe_future(res)
-        super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
+        res = super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
+        yield gen.maybe_future(res)
 
     def initialize(self):
         self.log.debug("Initializing websocket connection %s", self.request.path)
diff --git a/jupyter_server/utils.py b/jupyter_server/utils.py
@@ -12,12 +12,30 @@
 import sys
 from distutils.version import LooseVersion
 
+try:
+    from inspect import isawaitable
+except ImportError:
+    def isawaitable(f):
+        """If isawaitable is undefined, nothing is awaitable"""
+        return False
+
+try:
+    from concurrent.futures import Future as ConcurrentFuture
+except ImportError:
+    class ConcurrentFuture:
+        """If concurrent.futures isn't importable, nothing will be a c.f.Future"""
+        pass
+
 try:
     from urllib.parse import quote, unquote, urlparse
 except ImportError:
     from urllib import quote, unquote
     from urlparse import urlparse
 
+# tornado.concurrent.Future is asyncio.Future
+# in tornado >=5 with Python 3
+from tornado.concurrent import Future as TornadoFuture
+from tornado import gen
 from ipython_genutils import py3compat
 
 # UF_HIDDEN is a stat flag not defined in the stat module.
@@ -305,3 +323,32 @@ def _check_pid_posix(pid):
     check_pid = _check_pid_win32
 else:
     check_pid = _check_pid_posix
+
+
+def maybe_future(obj):
+    """Like tornado's gen.maybe_future
+    but more compatible with asyncio for recent versions
+    of tornado
+    """
+    if isinstance(obj, TornadoFuture):
+        return obj
+    elif isawaitable(obj):
+        return asyncio.ensure_future(obj)
+    elif isinstance(obj, ConcurrentFuture):
+        return asyncio.wrap_future(obj)
+    else:
+        # not awaitable, wrap scalar in future
+        f = TornadoFuture()
+        f.set_result(obj)
+        return f
+
+# monkeypatch tornado gen.maybe_future
+# on Python 3
+# TODO: remove monkeypatch after backporting smaller fix to 5.x
+try:
+    import asyncio
+except ImportError:
+    pass
+else:
+    import tornado.gen
+    tornado.gen.maybe_future = maybe_future
