From 1e36145dcd7640b631fd92a706adf807ed9a36b5 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Tue, 11 Feb 2020 16:43:02 +0100
Subject: [PATCH 01/20] Async cell execution

---
 .github/workflows/main.yml                    | 12 ++---
 .travis.yml                                   |  6 +--
 setup.py                                      |  6 ++-
 .../default/nbconvert_templates/lab.tpl       |  2 +-
 .../default/nbconvert_templates/voila.tpl     |  2 +-
 voila/app.py                                  |  4 +-
 voila/execute.py                              | 31 +++++------
 voila/exporter.py                             | 25 ++-------
 voila/handler.py                              | 38 ++++++++------
 voila/threading.py                            | 51 -------------------
 10 files changed, 58 insertions(+), 119 deletions(-)
 delete mode 100644 voila/threading.py

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 70aca8172..55f7ba384 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: [3.5, 3.6, 3.7]
+        python-version: [3.6, 3.7, 3.8]
 
     steps:
     - uses: actions/checkout@v1
@@ -34,25 +34,25 @@ jobs:
     - name: Update conda
       run: |
         conda update -y -n base conda setuptools
-    
+
     - name: Init conda
       run: |
         conda init bash
         conda info -a
 
     - name: Create the conda environment
-      run: conda create -q -y -n voila-tests -c conda-forge python=$PYTHON_VERSION pip jupyterlab_pygments==0.1.0 nbconvert=5.5 pytest-cov nodejs flake8 ipywidgets matplotlib xeus-cling
+      run: conda create -q -y -n voila-tests -c conda-forge python=$PYTHON_VERSION pip jupyterlab_pygments==0.1.0 pytest-cov nodejs flake8 ipywidgets matplotlib xeus-cling
       env:
         PYTHON_VERSION: ${{ matrix.python-version }}
 
-    - name: Install dependencies 
+    - name: Install dependencies
       run: |
         source "$CONDA/etc/profile.d/conda.sh"
         conda activate voila-tests
         whereis python
         python --version
-        
-        python -m pip install ".[test]"
+
+        python -m pip install --ignore-installed ".[test]"
         cd tests/test_template; pip install .; cd ../../;
 
     - name: Flake8
diff --git a/.travis.yml b/.travis.yml
index 32a733d9e..168ad5d4a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,9 +4,9 @@ os:
  - osx
 env:
  matrix:
-  - PYTHON_VERSION=3.5
   - PYTHON_VERSION=3.6
   - PYTHON_VERSION=3.7
+  - PYTHON_VERSION=3.8
 before_install:
   - if [[ $TRAVIS_OS_NAME == osx ]]; then ulimit -n 2048; fi
   - if [[ $TRAVIS_OS_NAME == linux ]]; then sudo apt-get update; fi
@@ -18,10 +18,10 @@ before_install:
   - conda config --set always_yes yes --set changeps1 no
   - conda update -q conda
   - conda info -a
-  - conda create -q -n test-environment -c conda-forge python=$PYTHON_VERSION jupyterlab_pygments==0.1.0 nbconvert=5.5 pytest-cov nodejs flake8 ipywidgets matplotlib xeus-cling
+  - conda create -q -n test-environment -c conda-forge python=$PYTHON_VERSION jupyterlab_pygments==0.1.0 pytest-cov nodejs flake8 ipywidgets matplotlib xeus-cling
   - source activate test-environment
 install:
-  - pip install ".[test]"
+  - pip install --ignore-installed ".[test]"
   - cd tests/test_template; pip install .; cd ../../;
 script:
   - VOILA_TEST_DEBUG=1 VOILA_TEST_XEUS_CLING=1 py.test tests/ --async-test-timeout=240
diff --git a/setup.py b/setup.py
index ad7a1b445..dd49cd4b1 100644
--- a/setup.py
+++ b/setup.py
@@ -377,7 +377,9 @@ def get_data_files():
     'install_requires': [
         'async_generator',
         'jupyter_server>=0.1.0,<0.2.0',
-        'nbconvert>=5.5.0,<6',
+        'jupyter_client>=6.0.0',
+        'nbclient @ git+https://github.com/jupyter/nbclient',
+        'nbconvert @ git+https://github.com/jupyter/nbconvert',
         'jupyterlab_pygments>=0.1.0,<0.2',
         'pygments>=2.4.1,<3'  # Explicitly requiring pygments which is a second-order dependency.
                               # An older versions is generally installed already and is otherwise not updated by pip.
@@ -385,7 +387,7 @@ def get_data_files():
     'extras_require': {
         'test': [
             'mock',
-            'pytest<4',
+            'pytest',
             'pytest-tornado',
             'matplotlib',
             'ipywidgets'
diff --git a/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl b/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
index c06cdf7d4..7ea3040b8 100644
--- a/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
+++ b/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
@@ -1,4 +1,4 @@
-{%- extends 'display_priority.tpl' -%}
+{%- extends 'display_priority.j2' -%}
 
 {% block codecell %}
 {%- if not cell.outputs -%}
diff --git a/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl b/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
index f9bf5409e..1e274cdfe 100644
--- a/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
+++ b/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
@@ -62,7 +62,7 @@ a.anchor-link {
 
 {%- block body_loop -%}
   {# from this point on, the kernel is started #}
-  {%- with kernel_id = kernel_start() -%}
+  {%- with kernel_id = kernel_start(nb) -%}
     <script id="jupyter-config-data" type="application/json">
     {
         "baseUrl": "{{resources.base_url}}",
diff --git a/voila/app.py b/voila/app.py
index c2a499bda..4d0308ce8 100644
--- a/voila/app.py
+++ b/voila/app.py
@@ -59,7 +59,7 @@
 from ._version import __version__
 from .static_file_handler import MultiStaticFileHandler, WhiteListFileHandler
 from .configuration import VoilaConfiguration
-from .execute import VoilaExecutePreprocessor
+from .execute import VoilaExecutor
 from .exporter import VoilaExporter
 from .csspreprocessor import VoilaCSSPreprocessor
 
@@ -129,7 +129,7 @@ class Voila(Application):
     }
     classes = [
         VoilaConfiguration,
-        VoilaExecutePreprocessor,
+        VoilaExecutor,
         VoilaExporter,
         VoilaCSSPreprocessor
     ]
diff --git a/voila/execute.py b/voila/execute.py
index c4aeaaa5a..bff6f26d1 100644
--- a/voila/execute.py
+++ b/voila/execute.py
@@ -11,7 +11,8 @@
 from time import monotonic
 
 from nbconvert.preprocessors import ClearOutputPreprocessor
-from nbconvert.preprocessors.execute import CellExecutionError, ExecutePreprocessor
+from nbclient.exceptions import CellExecutionError
+from nbclient import NotebookClient
 from nbformat.v4 import output_from_msg
 import zmq
 
@@ -113,7 +114,7 @@ def set_state(self, state):
                 self.msg_id = msg_id
 
 
-class VoilaExecutePreprocessor(ExecutePreprocessor):
+class VoilaExecutor(NotebookClient):
     """Execute, but respect the output widget behaviour"""
     cell_error_instruction = Unicode(
         'Please run Voila with --debug to see the error message.',
@@ -124,21 +125,21 @@ class VoilaExecutePreprocessor(ExecutePreprocessor):
     )
 
     cell_timeout_instruction = Unicode(
-        'Please run Voila with --VoilaExecutePreprocessor.interrupt_on_timeout=True to continue executing the rest of the notebook.',
+        'Please run Voila with --VoilaExecutor.interrupt_on_timeout=True to continue executing the rest of the notebook.',
         config=True,
         help=(
             'instruction given to user to continue execution on timeout'
         )
     )
 
-    def __init__(self, **kwargs):
-        super(VoilaExecutePreprocessor, self).__init__(**kwargs)
+    def __init__(self, nb, km=None, **kwargs):
+        super(VoilaExecutor, self).__init__(nb, km=km, **kwargs)
         self.output_hook_stack = collections.defaultdict(list)  # maps to list of hooks, where the last is used
         self.output_objects = {}
 
-    def preprocess(self, nb, resources, km=None):
+    def execute(self, nb, resources, km=None):
         try:
-            result = super(VoilaExecutePreprocessor, self).preprocess(nb, resources=resources, km=km)
+            result = super(VoilaExecutor, self).execute()
         except CellExecutionError as e:
             self.log.error(e)
             result = (nb, resources)
@@ -149,11 +150,11 @@ def preprocess(self, nb, resources, km=None):
 
         return result
 
-    def preprocess_cell(self, cell, resources, cell_index, store_history=True):
+    async def execute_cell(self, cell, resources, cell_index, store_history=True):
         try:
             # TODO: pass store_history as a 5th argument when we can require nbconver >=5.6.1
-            # result = super(VoilaExecutePreprocessor, self).preprocess_cell(cell, resources, cell_index, store_history)
-            result = super(VoilaExecutePreprocessor, self).preprocess_cell(cell, resources, cell_index)
+            # result = super(VoilaExecutor, self).execute_cell(cell, resources, cell_index, store_history)
+            result = await super(VoilaExecutor, self).async_execute_cell(cell, cell_index)
         except TimeoutError as e:
             self.log.error(e)
             self.show_code_cell_timeout(cell)
@@ -186,10 +187,10 @@ def output(self, outs, msg, display_id, cell_index):
             hook = self.output_hook_stack[parent_msg_id][-1]
             hook.output(outs, msg, display_id, cell_index)
             return
-        super(VoilaExecutePreprocessor, self).output(outs, msg, display_id, cell_index)
+        super(VoilaExecutor, self).output(outs, msg, display_id, cell_index)
 
     def handle_comm_msg(self, outs, msg, cell_index):
-        super(VoilaExecutePreprocessor, self).handle_comm_msg(outs, msg, cell_index)
+        super(VoilaExecutor, self).handle_comm_msg(outs, msg, cell_index)
         self.log.debug('comm msg: %r', msg)
         if msg['msg_type'] == 'comm_open' and msg['content'].get('target_name') == 'jupyter.widget':
             content = msg['content']
@@ -213,7 +214,7 @@ def clear_output(self, outs, msg, cell_index):
             hook = self.output_hook_stack[parent_msg_id][-1]
             hook.clear_output(outs, msg, cell_index)
             return
-        super(VoilaExecutePreprocessor, self).clear_output(outs, msg, cell_index)
+        super(VoilaExecutor, self).clear_output(outs, msg, cell_index)
 
     def strip_notebook_errors(self, nb):
         """Strip error messages and traceback from a Notebook."""
@@ -344,5 +345,5 @@ def executenb(nb, cwd=None, km=None, **kwargs):
         resources['metadata'] = {'path': cwd}  # pragma: no cover
     # Clear any stale output, in case of exception
     nb, resources = ClearOutputPreprocessor().preprocess(nb, resources)
-    ep = VoilaExecutePreprocessor(**kwargs)
-    return ep.preprocess(nb, resources, km=km)[0]
+    executor = VoilaExecutor(nb, km=km, **kwargs)
+    return executor.execute(nb, resources, km=km)
diff --git a/voila/exporter.py b/voila/exporter.py
index 6a03968b2..09ba269df 100644
--- a/voila/exporter.py
+++ b/voila/exporter.py
@@ -19,12 +19,6 @@
 from nbconvert.exporters.templateexporter import TemplateExporter
 from nbconvert.filters.highlight import Highlight2HTML
 
-from .threading import async_generator_to_thread
-
-# As long as we support Python35, we use this library to get as async
-# generators: https://pypi.org/project/async_generator/
-from async_generator import async_generator, yield_
-
 
 class VoilaMarkdownRenderer(IPythonRenderer):
     """Custom markdown renderer that inlines images"""
@@ -83,7 +77,6 @@ def _default_preprocessors(self):
     def default_template_file(self):
         return 'voila.tpl'
 
-    @async_generator
     async def generate_from_notebook_node(self, nb, resources=None, extra_context={}, **kw):
         # this replaces from_notebook_node, but calls template.generate instead of template.render
         langinfo = nb.metadata.get('language_info', {})
@@ -106,24 +99,12 @@ async def generate_from_notebook_node(self, nb, resources=None, extra_context={}
                 'no_prompt': self.exclude_input_prompt and self.exclude_output_prompt,
                 }
 
-        # Jinja with Python3.5 does not support async (generators), which
-        # means that it's not async all the way down. Which means that we
-        # cannot use coroutines for the cell_generator, and that they will
-        # block the IO loop. In that case we will run the iterator in a
-        # thread instead.
-
-        @async_generator_to_thread
-        @async_generator
-        async def async_jinja_generator():
-            # Top level variables are passed to the template_exporter here.
-            for output in self.template.generate(nb=nb_copy, resources=resources, **extra_context):
-                await yield_((output, resources))
-
-        async for output, resources in async_jinja_generator():
-            await yield_((output, resources))
+        async for output in self.template.generate_async(nb=nb_copy, resources=resources, **extra_context):
+            yield (output, resources)
 
     @property
     def environment(self):
+        self.enable_async = True
         env = super(type(self), self).environment
         if 'jinja2.ext.do' not in env.extensions:
             env.add_extension('jinja2.ext.do')
diff --git a/voila/handler.py b/voila/handler.py
index 78ff2c95f..c80d5de3d 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -18,7 +18,7 @@
 
 from nbconvert.preprocessors import ClearOutputPreprocessor
 
-from .execute import executenb, VoilaExecutePreprocessor
+from .execute import executenb, VoilaExecutor
 from .exporter import VoilaExporter
 
 
@@ -96,16 +96,11 @@ async def get(self, path=None):
         # Template should first call kernel_start, and then decide to use notebook_execute
         # or cell_generator to implement progressive cell rendering
         extra_context = {
-            # NOTE: we can remove the lambda is we use jinja's async feature, which will automatically await the future
-            'kernel_start': lambda: self._jinja_kernel_start().result(),  # pass the result (not the future) to the template
+            'kernel_start': self._jinja_kernel_start,
             'cell_generator': self._jinja_cell_generator,
             'notebook_execute': self._jinja_notebook_execute,
         }
 
-        # Currenly _jinja_kernel_start is executed from a different thread, which causes the websocket connection from
-        # the frontend to fail. Instead, we start it beforehand, and just return the kernel_id in _jinja_kernel_start
-        self.kernel_id = await tornado.gen.maybe_future(self.kernel_manager.start_kernel(kernel_name=self.notebook.metadata.kernelspec.name, path=self.cwd))
-
         # Compose reply
         self.set_header('Content-Type', 'text/html')
         # render notebook in snippets, and flush them out to the browser can render progresssively
@@ -118,12 +113,23 @@ async def get(self, path=None):
     def redirect_to_file(self, path):
         self.redirect(url_path_join(self.base_url, 'voila', 'files', path))
 
-    @tornado.gen.coroutine
-    def _jinja_kernel_start(self):
+    async def _jinja_kernel_start(self, nb):
         assert not self.kernel_started, "kernel was already started"
-        # See command above aboout not being able to start the kernel from a different thread
+        kernel_id = await self.kernel_manager.start_kernel(kernel_name=self.notebook.metadata.kernelspec.name, path=self.cwd)
+        km = self.kernel_manager.get_kernel(kernel_id)
+        km.client_class = 'jupyter_client.asynchronous.AsyncKernelClient'
+        self.executor = VoilaExecutor(nb, km=km, config=self.traitlet_config)
+        self.executor.kc = km.client()
+        self.executor.kc.start_channels()
+        try:
+            await self.executor.kc.wait_for_ready(timeout=self.executor.startup_timeout)
+        except RuntimeError:
+            self.executor.kc.stop_channels()
+            self.executor.km.shutdown_kernel()
+            raise
+        self.executor.kc.allow_stdin = False
         self.kernel_started = True
-        return self.kernel_id
+        return kernel_id
 
     def _jinja_notebook_execute(self, nb, kernel_id):
         km = self.kernel_manager.get_kernel(kernel_id)
@@ -133,12 +139,10 @@ def _jinja_notebook_execute(self, nb, kernel_id):
         # see the updated variable (it seems to be local to our block)
         nb.cells = result.cells
 
-    def _jinja_cell_generator(self, nb, kernel_id):
+    async def _jinja_cell_generator(self, nb, kernel_id):
         """Generator that will execute a single notebook cell at a time"""
-        km = self.kernel_manager.get_kernel(kernel_id)
-
         nb, resources = ClearOutputPreprocessor().preprocess(nb, {'metadata': {'path': self.cwd}})
-        ep = VoilaExecutePreprocessor(config=self.traitlet_config)
+        ep = VoilaExecutor(config=self.traitlet_config)
 
         stop_execution = False
         with ep.setup_preprocessor(nb, resources, km=km):
@@ -151,7 +155,9 @@ def _jinja_cell_generator(self, nb, kernel_id):
                     res = (cell, resources)
                     stop_execution = True
 
-                yield res[0]
+        for cell_idx, cell in enumerate(nb.cells):
+            res = await self.executor.execute_cell(cell, None, cell_idx, store_history=False)
+            yield res
 
     # @tornado.gen.coroutine
     async def load_notebook(self, path):
diff --git a/voila/threading.py b/voila/threading.py
deleted file mode 100644
index 2d260b22b..000000000
--- a/voila/threading.py
+++ /dev/null
@@ -1,51 +0,0 @@
-import asyncio
-import threading
-import tornado.queues
-
-# As long as we support Python35, we use this library to get as async
-# generators: https://pypi.org/project/async_generator/
-from async_generator import async_generator, yield_
-
-
-class ThreadedAsyncGenerator(threading.Thread):
-    def __init__(self, main_ioloop, fn, *args, **kwargs):
-        super(ThreadedAsyncGenerator, self).__init__()
-        self.main_ioloop = main_ioloop
-        self.fn = fn
-        self.args = args
-        self.kwargs = kwargs
-        self.queue = tornado.queues.Queue()
-        self.start()
-
-    def run(self):
-        ioloop_in_thread = asyncio.new_event_loop()
-        asyncio.set_event_loop(ioloop_in_thread)
-        return ioloop_in_thread.run_until_complete(self._run())
-
-    async def _run(self):
-        async for item in self.fn(*self.args, **self.kwargs):
-            def thread_safe_put(item=item):
-                self.queue.put(item)
-            self.main_ioloop.call_soon_threadsafe(thread_safe_put)
-
-        def thread_safe_end():
-            self.queue.put(StopIteration)
-        self.main_ioloop.call_soon_threadsafe(thread_safe_end)
-
-    @async_generator
-    async def __aiter__(self):
-        while True:
-            value = await self.queue.get()
-            if value == StopIteration:
-                break
-            await yield_(value)
-
-
-def async_generator_to_thread(fn):
-    """Calls an async generator function fn in a thread and async returns the results"""
-    ioloop = asyncio.get_event_loop()
-
-    def wrapper(*args, **kwargs):
-        gen = ThreadedAsyncGenerator(ioloop, fn, *args, **kwargs)
-        return gen
-    return wrapper

From 5effb39cb1e6541cb50373b6f723450bde85d463 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Wed, 11 Mar 2020 09:29:50 +0100
Subject: [PATCH 02/20] Use my branch of nbclient

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index dd49cd4b1..0834546e0 100644
--- a/setup.py
+++ b/setup.py
@@ -378,7 +378,7 @@ def get_data_files():
         'async_generator',
         'jupyter_server>=0.1.0,<0.2.0',
         'jupyter_client>=6.0.0',
-        'nbclient @ git+https://github.com/jupyter/nbclient',
+        'nbclient @ git+https://github.com/davidbrochart/nbclient@nest_asyncio',
         'nbconvert @ git+https://github.com/jupyter/nbconvert',
         'jupyterlab_pygments>=0.1.0,<0.2',
         'pygments>=2.4.1,<3'  # Explicitly requiring pygments which is a second-order dependency.

From fd54cb7267f7941fd49c05482e38864279e1721f Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 26 Mar 2020 07:20:48 +0100
Subject: [PATCH 03/20] Pin jupyter_client>=6.1.1

---
 setup.py                  |  4 +-
 tests/app/timeout_test.py |  2 +-
 voila/execute.py          | 81 ---------------------------------------
 voila/handler.py          | 19 ++++-----
 4 files changed, 10 insertions(+), 96 deletions(-)

diff --git a/setup.py b/setup.py
index 0834546e0..81a404d6a 100644
--- a/setup.py
+++ b/setup.py
@@ -377,8 +377,8 @@ def get_data_files():
     'install_requires': [
         'async_generator',
         'jupyter_server>=0.1.0,<0.2.0',
-        'jupyter_client>=6.0.0',
-        'nbclient @ git+https://github.com/davidbrochart/nbclient@nest_asyncio',
+        'jupyter_client>=6.1.1',
+        'nbclient @ git+https://github.com/jupyter/nbclient',
         'nbconvert @ git+https://github.com/jupyter/nbconvert',
         'jupyterlab_pygments>=0.1.0,<0.2',
         'pygments>=2.4.1,<3'  # Explicitly requiring pygments which is a second-order dependency.
diff --git a/tests/app/timeout_test.py b/tests/app/timeout_test.py
index df3c37fed..6c3885581 100644
--- a/tests/app/timeout_test.py
+++ b/tests/app/timeout_test.py
@@ -10,7 +10,7 @@ def voila_notebook(notebook_directory):
 
 @pytest.fixture
 def voila_args_extra():
-    return ['--VoilaExecutePreprocessor.timeout=1', '--KernelManager.shutdown_wait_time=0.1']
+    return ['--VoilaExecutor.timeout=1', '--KernelManager.shutdown_wait_time=0.1']
 
 
 @pytest.mark.gen_test
diff --git a/voila/execute.py b/voila/execute.py
index bff6f26d1..c0c0cac3e 100644
--- a/voila/execute.py
+++ b/voila/execute.py
@@ -8,13 +8,11 @@
 #############################################################################
 import collections
 import logging
-from time import monotonic
 
 from nbconvert.preprocessors import ClearOutputPreprocessor
 from nbclient.exceptions import CellExecutionError
 from nbclient import NotebookClient
 from nbformat.v4 import output_from_msg
-import zmq
 
 from traitlets import Unicode
 from ipykernel.jsonutil import json_clean
@@ -247,85 +245,6 @@ def strip_code_cell_errors(self, cell):
 
         return cell
 
-    # make it nbconvert 5.5 compatible
-    def _get_timeout(self, cell):
-        if self.timeout_func is not None and cell is not None:
-            timeout = self.timeout_func(cell)
-        else:
-            timeout = self.timeout
-
-        if not timeout or timeout < 0:
-            timeout = None
-
-        return timeout
-
-    # make it nbconvert 5.5 compatible
-    def _handle_timeout(self, timeout):
-        self.log.error(
-            "Timeout waiting for execute reply (%is)." % timeout)
-        if self.interrupt_on_timeout:
-            self.log.error("Interrupting kernel")
-            self.km.interrupt_kernel()
-        else:
-            raise TimeoutError("Cell execution timed out")
-
-    def run_cell(self, cell, cell_index=0, store_history=False):
-        parent_msg_id = self.kc.execute(cell.source, store_history=store_history, stop_on_error=not self.allow_errors)
-        self.log.debug("Executing cell:\n%s", cell.source)
-        exec_timeout = self._get_timeout(cell)
-        deadline = None
-        if exec_timeout is not None:
-            deadline = monotonic() + exec_timeout
-
-        cell.outputs = []
-        self.clear_before_next_output = False
-
-        # we need to have a reply, and return to idle before we can consider the cell executed
-        idle = False
-        execute_reply = None
-
-        deadline_passed = 0
-        deadline_passed_max = 5
-        while not idle or execute_reply is None:
-            # we want to timeout regularly, to see if the kernel is still alive
-            # this is tested in preprocessors/test/test_execute.py#test_kernel_death
-            # this actually fakes the kernel death, and we might be able to use the xlist
-            # to detect a disconnected kernel
-            timeout = min(1, deadline - monotonic())
-            # if we interrupt on timeout, we allow 1 seconds to pass till deadline
-            # to make sure we get the interrupt message
-            if timeout >= 0.0:
-                # we include 0, which simply is a poll to see if we have messages left
-                rlist = zmq.select([self.kc.iopub_channel.socket, self.kc.shell_channel.socket], [], [], timeout)[0]
-                if not rlist:
-                    self._check_alive()
-                    if monotonic() > deadline:
-                        self._handle_timeout(exec_timeout)
-                        deadline_passed += 1
-                        assert self.interrupt_on_timeout
-                        if deadline_passed <= deadline_passed_max:
-                            # when we interrupt, we want to do this multiple times, so we give some
-                            # extra time to handle the interrupt message
-                            deadline += self.iopub_timeout
-                if self.kc.shell_channel.socket in rlist:
-                    msg = self.kc.shell_channel.get_msg(block=False)
-                    if msg['parent_header'].get('msg_id') == parent_msg_id:
-                        execute_reply = msg
-                if self.kc.iopub_channel.socket in rlist:
-                    msg = self.kc.iopub_channel.get_msg(block=False)
-                    if msg['parent_header'].get('msg_id') == parent_msg_id:
-                        if msg['msg_type'] == 'status' and msg['content']['execution_state'] == 'idle':
-                            idle = True
-                        else:
-                            self.process_message(msg, cell, cell_index)
-                    else:
-                        self.log.debug("Received message for which we were not the parent: %s", msg)
-            else:
-                self._handle_timeout(exec_timeout)
-                break
-
-        return execute_reply, cell.outputs
-
     def show_code_cell_timeout(self, cell):
         """Show a timeout error output in a code cell."""
 
diff --git a/voila/handler.py b/voila/handler.py
index c80d5de3d..69276fcb5 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -142,21 +142,16 @@ def _jinja_notebook_execute(self, nb, kernel_id):
     async def _jinja_cell_generator(self, nb, kernel_id):
         """Generator that will execute a single notebook cell at a time"""
         nb, resources = ClearOutputPreprocessor().preprocess(nb, {'metadata': {'path': self.cwd}})
-        ep = VoilaExecutor(config=self.traitlet_config)
 
         stop_execution = False
-        with ep.setup_preprocessor(nb, resources, km=km):
-            for cell_idx, cell in enumerate(nb.cells):
-                if stop_execution:
-                    break
-                try:
-                    res = ep.preprocess_cell(cell, resources, cell_idx, store_history=False)
-                except TimeoutError:
-                    res = (cell, resources)
-                    stop_execution = True
-
         for cell_idx, cell in enumerate(nb.cells):
-            res = await self.executor.execute_cell(cell, None, cell_idx, store_history=False)
+            if stop_execution:
+                break
+            try:
+                res = await self.executor.execute_cell(cell, None, cell_idx, store_history=False)
+            except TimeoutError:
+                res = cell
+                stop_execution = True
             yield res
 
     # @tornado.gen.coroutine

From d4c55afa191d1b6722b418ff518696ac3acddafe Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Tue, 31 Mar 2020 22:03:09 +0200
Subject: [PATCH 04/20] Pin nbclient>=0.2.0

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index 81a404d6a..a40c666c5 100644
--- a/setup.py
+++ b/setup.py
@@ -378,7 +378,7 @@ def get_data_files():
         'async_generator',
         'jupyter_server>=0.1.0,<0.2.0',
         'jupyter_client>=6.1.1',
-        'nbclient @ git+https://github.com/jupyter/nbclient',
+        'nbclient>=0.2.0',
         'nbconvert @ git+https://github.com/jupyter/nbconvert',
         'jupyterlab_pygments>=0.1.0,<0.2',
         'pygments>=2.4.1,<3'  # Explicitly requiring pygments which is a second-order dependency.

From b51fc7ee91acc46ed59915834985926029e336a6 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Fri, 10 Apr 2020 10:20:31 +0200
Subject: [PATCH 05/20] Use AsyncMappingKernelManager

---
 setup.py         | 6 +++---
 voila/app.py     | 8 ++++----
 voila/handler.py | 2 --
 3 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/setup.py b/setup.py
index a40c666c5..d671ca12f 100644
--- a/setup.py
+++ b/setup.py
@@ -376,10 +376,10 @@ def get_data_files():
     },
     'install_requires': [
         'async_generator',
-        'jupyter_server>=0.1.0,<0.2.0',
-        'jupyter_client>=6.1.1',
+        'jupyter_server @ git+https://github.com/jupyter/jupyter_server',
+        'jupyter_client @ git+https://github.com/jupyter/jupyter_client',
         'nbclient>=0.2.0',
-        'nbconvert @ git+https://github.com/jupyter/nbconvert',
+        'nbconvert==6.0.0a1',
         'jupyterlab_pygments>=0.1.0,<0.2',
         'pygments>=2.4.1,<3'  # Explicitly requiring pygments which is a second-order dependency.
                               # An older versions is generally installed already and is otherwise not updated by pip.
diff --git a/voila/app.py b/voila/app.py
index 4d0308ce8..17d9f33af 100644
--- a/voila/app.py
+++ b/voila/app.py
@@ -39,12 +39,12 @@
 from traitlets.config.loader import Config
 from traitlets import Unicode, Integer, Bool, Dict, List, default
 
-from jupyter_server.services.kernels.kernelmanager import MappingKernelManager
+from jupyter_server.services.kernels.kernelmanager import AsyncMappingKernelManager
 from jupyter_server.services.kernels.handlers import KernelHandler, ZMQChannelsHandler
 from jupyter_server.services.contents.largefilemanager import LargeFileManager
 from jupyter_server.base.handlers import FileFindHandler, path_regex
 from jupyter_server.config_manager import recursive_update
-from jupyter_server.utils import url_path_join
+from jupyter_server.utils import url_path_join, run_sync
 from jupyter_server.services.config import ConfigManager
 
 from jupyter_client.kernelspec import KernelSpecManager
@@ -392,7 +392,7 @@ def start(self):
             parent=self
         )
 
-        self.kernel_manager = MappingKernelManager(
+        self.kernel_manager = AsyncMappingKernelManager(
             parent=self,
             connection_dir=self.connection_dir,
             kernel_spec_manager=self.kernel_spec_manager,
@@ -510,7 +510,7 @@ def start(self):
 
     def stop(self):
         shutil.rmtree(self.connection_dir)
-        self.kernel_manager.shutdown_all()
+        run_sync(self.kernel_manager.shutdown_all())
 
     def random_ports(self, port, n):
         """Generate a list of n random ports near the given port.
diff --git a/voila/handler.py b/voila/handler.py
index 69276fcb5..d66387600 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -117,7 +117,6 @@ async def _jinja_kernel_start(self, nb):
         assert not self.kernel_started, "kernel was already started"
         kernel_id = await self.kernel_manager.start_kernel(kernel_name=self.notebook.metadata.kernelspec.name, path=self.cwd)
         km = self.kernel_manager.get_kernel(kernel_id)
-        km.client_class = 'jupyter_client.asynchronous.AsyncKernelClient'
         self.executor = VoilaExecutor(nb, km=km, config=self.traitlet_config)
         self.executor.kc = km.client()
         self.executor.kc.start_channels()
@@ -154,7 +153,6 @@ async def _jinja_cell_generator(self, nb, kernel_id):
                 stop_execution = True
             yield res
 
-    # @tornado.gen.coroutine
     async def load_notebook(self, path):
         model = self.contents_manager.get(path=path)
         if 'content' not in model:

From d891e53e7d7a297a3816b1cf6f03d81f09946c76 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Fri, 10 Apr 2020 10:30:38 +0200
Subject: [PATCH 06/20] Install pytest-tornasync

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index d671ca12f..def1f8017 100644
--- a/setup.py
+++ b/setup.py
@@ -388,7 +388,7 @@ def get_data_files():
         'test': [
             'mock',
             'pytest',
-            'pytest-tornado',
+            'pytest-tornasync',
             'matplotlib',
             'ipywidgets'
         ]

From b5c28052f3fcb512605e6885bfcd943120889b77 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Tue, 14 Apr 2020 10:16:59 +0200
Subject: [PATCH 07/20] Pin jupyter_client>=6.1.3

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index def1f8017..dfd190e1b 100644
--- a/setup.py
+++ b/setup.py
@@ -377,7 +377,7 @@ def get_data_files():
     'install_requires': [
         'async_generator',
         'jupyter_server @ git+https://github.com/jupyter/jupyter_server',
-        'jupyter_client @ git+https://github.com/jupyter/jupyter_client',
+        'jupyter_client>=6.1.3',
         'nbclient>=0.2.0',
         'nbconvert==6.0.0a1',
         'jupyterlab_pygments>=0.1.0,<0.2',

From 50f467dbcbdbd2ccfd825915b6d477871dc16bc9 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 09:09:57 +0200
Subject: [PATCH 08/20] Pin jupyter_server>=0.3.0

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index dfd190e1b..c6b97b3e4 100644
--- a/setup.py
+++ b/setup.py
@@ -376,7 +376,7 @@ def get_data_files():
     },
     'install_requires': [
         'async_generator',
-        'jupyter_server @ git+https://github.com/jupyter/jupyter_server',
+        'jupyter_server>=0.3.0',
         'jupyter_client>=6.1.3',
         'nbclient>=0.2.0',
         'nbconvert==6.0.0a1',

From 8d4eba6ca52724e024b2c68550e8b0b06bfc1cc0 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 09:33:58 +0200
Subject: [PATCH 09/20] Add libgbm to fix puppeteer issue

---
 .github/workflows/build.yml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3c90af031..f1cdc4f19 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -16,6 +16,10 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v1
+    - name: install dependencies
+      run: |
+        sudo apt update
+        sudo apt-get install -y --no-install-recommends libgbm-dev
     - name: Install node
       uses: actions/setup-node@v1
       with:

From 607227bdbed2e38e3ab596b095f07b24262018f5 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 13:38:10 +0200
Subject: [PATCH 10/20] Use native coroutines in tests

---
 tests/app/config_paths_test.py         |  5 ++---
 tests/app/cwd_subdir_test.py           |  7 +++----
 tests/app/cwd_test.py                  |  5 ++---
 tests/app/execute_cpp_test.py          |  7 +++----
 tests/app/execute_test.py              | 20 +++++++++-----------
 tests/app/image_inlining_test.py       |  5 ++---
 tests/app/many_iopub_messages_test.py  |  5 ++---
 tests/app/nbextensions_test.py         |  5 ++---
 tests/app/no_kernelspec_test.py        |  7 +++----
 tests/app/no_strip_sources_test.py     |  5 ++---
 tests/app/non_existing_kernel_test.py  |  7 +++----
 tests/app/notebooks_test.py            |  5 ++---
 tests/app/serve_directory_test.py      | 15 ++++++---------
 tests/app/template_arg_test.py         |  5 ++---
 tests/app/template_cli_test.py         |  5 ++---
 tests/app/template_config_file_test.py |  5 ++---
 tests/app/template_custom_test.py      |  5 ++---
 tests/app/timeout_test.py              |  5 ++---
 tests/app/tree_test.py                 |  5 ++---
 tests/conftest.py                      |  2 +-
 tests/server/cwd_subdir_test.py        |  7 +++----
 tests/server/execute_cpp_test.py       |  7 +++----
 tests/server/execute_test.py           |  5 ++---
 tests/server/nbextensions_test.py      |  5 ++---
 tests/server/no_strip_sources_test.py  |  5 ++---
 tests/server/tree_test.py              |  5 ++---
 26 files changed, 68 insertions(+), 96 deletions(-)

diff --git a/tests/app/config_paths_test.py b/tests/app/config_paths_test.py
index aceed7fc9..4d258eba9 100644
--- a/tests/app/config_paths_test.py
+++ b/tests/app/config_paths_test.py
@@ -26,9 +26,8 @@ def test_config_contents_manager(voila_app):
     assert voila_app.contents_manager.use_atomic_writing is False
 
 
-@pytest.mark.gen_test
-def test_template(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_template(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     assert 'test_template.css' in response.body.decode('utf-8')
     assert 'Hi Voila' in response.body.decode('utf-8')
diff --git a/tests/app/cwd_subdir_test.py b/tests/app/cwd_subdir_test.py
index ab8834aad..50a7e365e 100644
--- a/tests/app/cwd_subdir_test.py
+++ b/tests/app/cwd_subdir_test.py
@@ -4,7 +4,7 @@
 
 @pytest.fixture
 def cwd_subdir_notebook_url(base_url):
-    return base_url + "/voila/render/subdir/cwd_subdir.ipynb"
+    return base_url + "voila/render/subdir/cwd_subdir.ipynb"
 
 
 @pytest.fixture
@@ -12,8 +12,7 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory, '--VoilaTest.log_level=DEBUG'] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_hello_world(http_client, cwd_subdir_notebook_url):
-    response = yield http_client.fetch(cwd_subdir_notebook_url)
+async def test_hello_world(http_server_client, cwd_subdir_notebook_url):
+    response = await http_server_client.fetch(cwd_subdir_notebook_url)
     html_text = response.body.decode('utf-8')
     assert 'check for the cwd' in html_text
diff --git a/tests/app/cwd_test.py b/tests/app/cwd_test.py
index 7bf1152f5..54a78c6fd 100644
--- a/tests/app/cwd_test.py
+++ b/tests/app/cwd_test.py
@@ -9,8 +9,7 @@ def voila_notebook(notebook_directory):
     return os.path.join(notebook_directory, 'cwd.ipynb')
 
 
-@pytest.mark.gen_test
-def test_template_cwd(http_client, base_url, notebook_directory):
-    response = yield http_client.fetch(base_url)
+async def test_template_cwd(http_server_client, base_url, notebook_directory):
+    response = await http_server_client.fetch(base_url)
     html_text = response.body.decode('utf-8')
     assert 'check for the cwd' in html_text
diff --git a/tests/app/execute_cpp_test.py b/tests/app/execute_cpp_test.py
index 5cbd5c5aa..abc9afc57 100644
--- a/tests/app/execute_cpp_test.py
+++ b/tests/app/execute_cpp_test.py
@@ -6,7 +6,7 @@
 
 @pytest.fixture
 def cpp_file_url(base_url):
-    return base_url + "/voila/render/print.xcpp"
+    return base_url + "voila/render/print.xcpp"
 
 
 @pytest.fixture
@@ -20,8 +20,7 @@ def voila_args(notebook_directory, voila_args_extra):
 
 
 @pytest.mark.skipif(not TEST_XEUS_CLING, reason='opt in to avoid having to install xeus-cling')
-@pytest.mark.gen_test
-def test_non_existing_kernel(http_client, cpp_file_url):
-    response = yield http_client.fetch(cpp_file_url)
+async def test_non_existing_kernel(http_server_client, cpp_file_url):
+    response = await http_server_client.fetch(cpp_file_url)
     assert response.code == 200
     assert 'Hello voila, from c++' in response.body.decode('utf-8')
diff --git a/tests/app/execute_test.py b/tests/app/execute_test.py
index 3aecb2c6d..546164064 100644
--- a/tests/app/execute_test.py
+++ b/tests/app/execute_test.py
@@ -2,10 +2,10 @@
 import pytest
 
 import tornado.web
-import tornado.gen
 
 import re
 import json
+import asyncio
 
 try:
     from unittest import mock
@@ -13,9 +13,8 @@
     import mock
 
 
-@pytest.mark.gen_test
-def test_hello_world(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_hello_world(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
@@ -23,19 +22,18 @@ def test_hello_world(http_client, base_url):
     assert 'test_template.css' not in html_text, "test_template should not be the default"
 
 
-@pytest.mark.gen_test
-def test_no_execute_allowed(voila_app, app, http_client, base_url):
+async def test_no_execute_allowed(voila_app, app, http_server_client, base_url):
     assert voila_app.app is app
-    response = (yield http_client.fetch(base_url)).body.decode('utf-8')
+    response = (await http_server_client.fetch(base_url)).body.decode('utf-8')
     pattern = r"""kernelId": ["']([0-9a-zA-Z-]+)["']"""
     groups = re.findall(pattern, response)
     kernel_id = groups[0]
     print(kernel_id, base_url)
     session_id = '445edd75-c6f5-45d2-8b58-5fe8f84a7123'
-    url = '{base_url}/api/kernels/{kernel_id}/channels?session_id={session_id}'.format(
+    url = '{base_url}api/kernels/{kernel_id}/channels?session_id={session_id}'.format(
         kernel_id=kernel_id, base_url=base_url, session_id=session_id
     ).replace('http://', 'ws://')
-    conn = yield tornado.websocket.websocket_connect(url)
+    conn = await tornado.websocket.websocket_connect(url)
 
     msg = {
         "header": {
@@ -59,8 +57,8 @@ def test_no_execute_allowed(voila_app, app, http_client, base_url):
         "channel": "shell",
     }
     with mock.patch.object(voila_app.log, 'warning') as mock_warning:
-        yield conn.write_message(json.dumps(msg))
+        await conn.write_message(json.dumps(msg))
         # make sure the warning method is called
         while not mock_warning.called:
-            yield tornado.gen.sleep(0.1)
+            await asyncio.sleep(0.1)
     mock_warning.assert_called_with('Received message of type "execute_request", which is not allowed. Ignoring.')
diff --git a/tests/app/image_inlining_test.py b/tests/app/image_inlining_test.py
index 5c15e21f6..eedd51219 100644
--- a/tests/app/image_inlining_test.py
+++ b/tests/app/image_inlining_test.py
@@ -11,9 +11,8 @@ def voila_notebook(notebook_directory):
     return os.path.join(notebook_directory, 'images.ipynb')
 
 
-@pytest.mark.gen_test
-def test_image_inlining(http_client, base_url, notebook_directory):
-    response = yield http_client.fetch(base_url)
+async def test_image_inlining(http_server_client, base_url, notebook_directory):
+    response = await http_server_client.fetch(base_url)
     html_text = response.body.decode('utf-8')
 
     assert 'data:image/svg+xml;base64,' in html_text
diff --git a/tests/app/many_iopub_messages_test.py b/tests/app/many_iopub_messages_test.py
index 5842c3f28..0cbf57653 100644
--- a/tests/app/many_iopub_messages_test.py
+++ b/tests/app/many_iopub_messages_test.py
@@ -26,8 +26,7 @@ def _close():
     return client
 
 
-@pytest.mark.gen_test
-def test_template_cwd(http_client, base_url, notebook_directory):
-    response = yield http_client.fetch(base_url)
+async def test_template_cwd(http_server_client, base_url, notebook_directory):
+    response = await http_server_client.fetch(base_url)
     html_text = response.body.decode('utf-8')
     assert 'you should see me' in html_text
diff --git a/tests/app/nbextensions_test.py b/tests/app/nbextensions_test.py
index 1ec72010d..7be69b897 100644
--- a/tests/app/nbextensions_test.py
+++ b/tests/app/nbextensions_test.py
@@ -22,9 +22,8 @@ def voila_config_file_paths_arg():
     return '--VoilaTest.config_file_paths=[%r]' % path
 
 
-@pytest.mark.gen_test
-def test_lists_extension(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_lists_extension(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
diff --git a/tests/app/no_kernelspec_test.py b/tests/app/no_kernelspec_test.py
index 451dfde85..11a13fda5 100644
--- a/tests/app/no_kernelspec_test.py
+++ b/tests/app/no_kernelspec_test.py
@@ -3,7 +3,7 @@
 
 @pytest.fixture
 def non_existing_kernel_notebook(base_url):
-    return base_url + "/voila/render/no_kernelspec.ipynb"
+    return base_url + "voila/render/no_kernelspec.ipynb"
 
 
 @pytest.fixture
@@ -11,8 +11,7 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_non_existing_kernel(http_client, non_existing_kernel_notebook):
-    response = yield http_client.fetch(non_existing_kernel_notebook)
+async def test_non_existing_kernel(http_server_client, non_existing_kernel_notebook):
+    response = await http_server_client.fetch(non_existing_kernel_notebook)
     assert response.code == 200
     assert 'Executing without a kernelspec' in response.body.decode('utf-8')
diff --git a/tests/app/no_strip_sources_test.py b/tests/app/no_strip_sources_test.py
index f54cf8718..b29394ec2 100644
--- a/tests/app/no_strip_sources_test.py
+++ b/tests/app/no_strip_sources_test.py
@@ -11,9 +11,8 @@ def voila_args_extra():
     return ['--VoilaConfiguration.strip_sources=False']
 
 
-@pytest.mark.gen_test
-def test_no_strip_sources(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_no_strip_sources(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
diff --git a/tests/app/non_existing_kernel_test.py b/tests/app/non_existing_kernel_test.py
index e588f8752..cd24824ef 100644
--- a/tests/app/non_existing_kernel_test.py
+++ b/tests/app/non_existing_kernel_test.py
@@ -3,7 +3,7 @@
 
 @pytest.fixture
 def non_existing_kernel_notebook(base_url):
-    return base_url + "/voila/render/non_existing_kernel.ipynb"
+    return base_url + "voila/render/non_existing_kernel.ipynb"
 
 
 @pytest.fixture
@@ -11,8 +11,7 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_non_existing_kernel(http_client, non_existing_kernel_notebook):
-    response = yield http_client.fetch(non_existing_kernel_notebook)
+async def test_non_existing_kernel(http_server_client, non_existing_kernel_notebook):
+    response = await http_server_client.fetch(non_existing_kernel_notebook)
     assert response.code == 200
     assert 'non-existing kernel' in response.body.decode('utf-8')
diff --git a/tests/app/notebooks_test.py b/tests/app/notebooks_test.py
index c3b9c0b34..5cf91ace2 100644
--- a/tests/app/notebooks_test.py
+++ b/tests/app/notebooks_test.py
@@ -7,8 +7,7 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory, '--VoilaTest.log_level=DEBUG'] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_other_comms(http_client, base_url):
-    response = yield http_client.fetch(base_url + '/voila/render/other_comms.ipynb')
+async def test_other_comms(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url + '/voila/render/other_comms.ipynb')
     html_text = response.body.decode('utf-8')
     assert 'This notebook executed' in html_text
diff --git a/tests/app/serve_directory_test.py b/tests/app/serve_directory_test.py
index 6f5ba4c30..86a61f044 100644
--- a/tests/app/serve_directory_test.py
+++ b/tests/app/serve_directory_test.py
@@ -10,10 +10,9 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory, '--VoilaTest.log_level=DEBUG'] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_print(http_client, print_notebook_url):
+async def test_print(http_server_client, print_notebook_url):
     print(print_notebook_url)
-    response = yield http_client.fetch(print_notebook_url)
+    response = await http_server_client.fetch(print_notebook_url)
     assert response.code == 200
     assert 'Hi Voila' in response.body.decode('utf-8')
 
@@ -23,18 +22,16 @@ def voila_args_extra():
     return ['--VoilaConfiguration.extension_language_mapping={".py": "python"}']
 
 
-@pytest.mark.gen_test
-def test_print_py(http_client, print_notebook_url):
+async def test_print_py(http_server_client, print_notebook_url):
     print(print_notebook_url)
-    response = yield http_client.fetch(print_notebook_url.replace('ipynb', 'py'))
+    response = await http_server_client.fetch(print_notebook_url.replace('ipynb', 'py'))
     assert response.code == 200
     assert 'Hi Voila' in response.body.decode('utf-8')
 
 
 @pytest.mark.skipif(not TEST_XEUS_CLING, reason='opt in to avoid having to install xeus-cling')
-@pytest.mark.gen_test
-def test_print_julia_notebook(http_client, print_notebook_url):
+async def test_print_julia_notebook(http_server_client, print_notebook_url):
     print(print_notebook_url)
-    response = yield http_client.fetch(print_notebook_url.replace('.ipynb', '_cpp.ipynb'))
+    response = await http_server_client.fetch(print_notebook_url.replace('.ipynb', '_cpp.ipynb'))
     assert response.code == 200
     assert 'Hi Voila, from c++' in response.body.decode('utf-8')
diff --git a/tests/app/template_arg_test.py b/tests/app/template_arg_test.py
index 4c4066c29..0f6a82221 100644
--- a/tests/app/template_arg_test.py
+++ b/tests/app/template_arg_test.py
@@ -7,9 +7,8 @@ def voila_args_extra():
     return ['--template=test_template']
 
 
-@pytest.mark.gen_test
-def test_template(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_template(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     assert 'test_template.css' in response.body.decode('utf-8')
     assert 'Hi Voila' in response.body.decode('utf-8')
diff --git a/tests/app/template_cli_test.py b/tests/app/template_cli_test.py
index 2bfbcd8fc..e9da1d271 100644
--- a/tests/app/template_cli_test.py
+++ b/tests/app/template_cli_test.py
@@ -13,8 +13,7 @@ def voila_args_extra():
     return ['--template=None', '--Voila.nbconvert_template_paths=[%r, %r]' % (path_test_template, path_default)]
 
 
-@pytest.mark.gen_test
-def test_template_test(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_template_test(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     assert 'test_template.css' in response.body.decode('utf-8')
diff --git a/tests/app/template_config_file_test.py b/tests/app/template_config_file_test.py
index 1242f5fc8..646965c38 100644
--- a/tests/app/template_config_file_test.py
+++ b/tests/app/template_config_file_test.py
@@ -13,9 +13,8 @@ def voila_args_extra():
     return ['--template=test_template', '--Voila.nbconvert_template_paths=[%r, %r]' % (path_test_template, path_default)]
 
 
-@pytest.mark.gen_test
-def test_template_test(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_template_test(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     assert 'test_template.css' in response.body.decode('utf-8')
     assert 'Hi Voila' in response.body.decode('utf-8')
diff --git a/tests/app/template_custom_test.py b/tests/app/template_custom_test.py
index 08dab9c88..abcba3c2a 100644
--- a/tests/app/template_custom_test.py
+++ b/tests/app/template_custom_test.py
@@ -23,9 +23,8 @@ def config(app):
     return config
 
 
-@pytest.mark.gen_test
-def test_template(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_template(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     assert 'test_template.css' in response.body.decode('utf-8')
     assert 'Hi Voila' in response.body.decode('utf-8')
diff --git a/tests/app/timeout_test.py b/tests/app/timeout_test.py
index 6c3885581..71a341173 100644
--- a/tests/app/timeout_test.py
+++ b/tests/app/timeout_test.py
@@ -13,8 +13,7 @@ def voila_args_extra():
     return ['--VoilaExecutor.timeout=1', '--KernelManager.shutdown_wait_time=0.1']
 
 
-@pytest.mark.gen_test
-def test_timeout(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_timeout(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     html_text = response.body.decode('utf-8')
     assert 'Cell execution timed out' in html_text
diff --git a/tests/app/tree_test.py b/tests/app/tree_test.py
index be6fc64f7..e5cf46513 100644
--- a/tests/app/tree_test.py
+++ b/tests/app/tree_test.py
@@ -12,9 +12,8 @@ def voila_args_extra():
     return ['--VoilaConfiguration.extension_language_mapping={".xcpp": "C++11"}']
 
 
-@pytest.mark.gen_test
-def test_tree(http_client, base_url):
-    response = yield http_client.fetch(base_url)
+async def test_tree(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url)
     assert response.code == 200
     text = response.body.decode('utf-8')
     assert 'print.ipynb' in text, 'tree handler should render ipynb files'
diff --git a/tests/conftest.py b/tests/conftest.py
index f3120f890..d19e0e3ac 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,7 +14,7 @@ def notebook_directory():
 
 @pytest.fixture
 def print_notebook_url(base_url):
-    return base_url + "/voila/render/print.ipynb"
+    return base_url + "voila/render/print.ipynb"
 
 
 @pytest.fixture
diff --git a/tests/server/cwd_subdir_test.py b/tests/server/cwd_subdir_test.py
index 6bdad3d13..8fd57614a 100644
--- a/tests/server/cwd_subdir_test.py
+++ b/tests/server/cwd_subdir_test.py
@@ -5,7 +5,7 @@
 
 @pytest.fixture
 def cwd_subdir_notebook_url(base_url):
-    return base_url + "/voila/render/subdir/cwd_subdir.ipynb"
+    return base_url + "voila/render/subdir/cwd_subdir.ipynb"
 
 
 @pytest.fixture
@@ -13,8 +13,7 @@ def voila_args(notebook_directory, voila_args_extra):
     return ['--VoilaTest.root_dir=%r' % notebook_directory, '--VoilaTest.log_level=DEBUG'] + voila_args_extra
 
 
-@pytest.mark.gen_test
-def test_hello_world(http_client, cwd_subdir_notebook_url):
-    response = yield http_client.fetch(cwd_subdir_notebook_url)
+async def test_hello_world(http_server_client, cwd_subdir_notebook_url):
+    response = await http_server_client.fetch(cwd_subdir_notebook_url)
     html_text = response.body.decode('utf-8')
     assert 'check for the cwd' in html_text
diff --git a/tests/server/execute_cpp_test.py b/tests/server/execute_cpp_test.py
index 9684e7439..dbaab47f7 100644
--- a/tests/server/execute_cpp_test.py
+++ b/tests/server/execute_cpp_test.py
@@ -6,7 +6,7 @@
 
 @pytest.fixture
 def cpp_file_url(base_url):
-    return base_url + "/voila/render/print.xcpp"
+    return base_url + "voila/render/print.xcpp"
 
 
 @pytest.fixture
@@ -20,8 +20,7 @@ def voila_args(notebook_directory, voila_args_extra):
 
 
 @pytest.mark.skipif(not TEST_XEUS_CLING, reason='opt in to avoid having to install xeus-cling')
-@pytest.mark.gen_test
-def test_non_existing_kernel(http_client, cpp_file_url):
-    response = yield http_client.fetch(cpp_file_url)
+async def test_non_existing_kernel(http_server_client, cpp_file_url):
+    response = await http_server_client.fetch(cpp_file_url)
     assert response.code == 200
     assert 'Hello voila, from c++' in response.body.decode('utf-8')
diff --git a/tests/server/execute_test.py b/tests/server/execute_test.py
index 692151a1f..2c12642de 100644
--- a/tests/server/execute_test.py
+++ b/tests/server/execute_test.py
@@ -2,9 +2,8 @@
 import pytest
 
 
-@pytest.mark.gen_test
-def test_hello_world(http_client, print_notebook_url):
-    response = yield http_client.fetch(print_notebook_url)
+async def test_hello_world(http_server_client, print_notebook_url):
+    response = await http_server_client.fetch(print_notebook_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
diff --git a/tests/server/nbextensions_test.py b/tests/server/nbextensions_test.py
index 66a057652..907e4367c 100644
--- a/tests/server/nbextensions_test.py
+++ b/tests/server/nbextensions_test.py
@@ -16,9 +16,8 @@ def config(app):
 
 
 @pytest.mark.xfail(reason='needs to be fixed')
-@pytest.mark.gen_test
-def test_lists_extension(http_client, print_notebook_url):
-    response = yield http_client.fetch(print_notebook_url)
+async def test_lists_extension(http_server_client, print_notebook_url):
+    response = await http_server_client.fetch(print_notebook_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
diff --git a/tests/server/no_strip_sources_test.py b/tests/server/no_strip_sources_test.py
index 47cd20976..f4ae21a75 100644
--- a/tests/server/no_strip_sources_test.py
+++ b/tests/server/no_strip_sources_test.py
@@ -11,9 +11,8 @@ def jupyter_server_args_extra():
     return ['--VoilaConfiguration.strip_sources=False']
 
 
-@pytest.mark.gen_test
-def test_hello_world(http_client, print_notebook_url):
-    response = yield http_client.fetch(print_notebook_url)
+async def test_hello_world(http_server_client, print_notebook_url):
+    response = await http_server_client.fetch(print_notebook_url)
     assert response.code == 200
     html_text = response.body.decode('utf-8')
     assert 'Hi Voila' in html_text
diff --git a/tests/server/tree_test.py b/tests/server/tree_test.py
index 3846abc70..d09ca1c75 100644
--- a/tests/server/tree_test.py
+++ b/tests/server/tree_test.py
@@ -12,9 +12,8 @@ def jupyter_server_args_extra():
     return ['--VoilaConfiguration.extension_language_mapping={".xcpp": "C++11"}']
 
 
-@pytest.mark.gen_test
-def test_tree(http_client, base_url):
-    response = yield http_client.fetch(base_url+'/voila/tree')
+async def test_tree(http_server_client, base_url):
+    response = await http_server_client.fetch(base_url+'voila/tree')
     assert response.code == 200
     text = response.body.decode('utf-8')
     assert 'print.ipynb' in text, 'tree handler should render ipynb files'

From d16bb22900d3a98e6b0f6cfe8421c6d85fc39dd2 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 13:46:41 +0200
Subject: [PATCH 11/20] Fix linter

---
 tests/app/execute_test.py    | 2 --
 tests/server/execute_test.py | 1 -
 2 files changed, 3 deletions(-)

diff --git a/tests/app/execute_test.py b/tests/app/execute_test.py
index 546164064..b282ba510 100644
--- a/tests/app/execute_test.py
+++ b/tests/app/execute_test.py
@@ -1,6 +1,4 @@
 # test basics of voila running a notebook
-import pytest
-
 import tornado.web
 
 import re
diff --git a/tests/server/execute_test.py b/tests/server/execute_test.py
index 2c12642de..a55f9793c 100644
--- a/tests/server/execute_test.py
+++ b/tests/server/execute_test.py
@@ -1,5 +1,4 @@
 # test basics of voila running a notebook
-import pytest
 
 
 async def test_hello_world(http_server_client, print_notebook_url):

From 83e8c10eef65f805fe825fb394b2dd4ca382146b Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 14:00:11 +0200
Subject: [PATCH 12/20] Fix URL

---
 tests/app/notebooks_test.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/app/notebooks_test.py b/tests/app/notebooks_test.py
index 5cf91ace2..3f10272e7 100644
--- a/tests/app/notebooks_test.py
+++ b/tests/app/notebooks_test.py
@@ -8,6 +8,6 @@ def voila_args(notebook_directory, voila_args_extra):
 
 
 async def test_other_comms(http_server_client, base_url):
-    response = await http_server_client.fetch(base_url + '/voila/render/other_comms.ipynb')
+    response = await http_server_client.fetch(base_url + 'voila/render/other_comms.ipynb')
     html_text = response.body.decode('utf-8')
     assert 'This notebook executed' in html_text

From 3a1c188dbfe4c9d4c25900457be9404df167d8a6 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 14:39:11 +0200
Subject: [PATCH 13/20] Fix websocket URL

---
 tests/app/execute_test.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tests/app/execute_test.py b/tests/app/execute_test.py
index b282ba510..9cca66c82 100644
--- a/tests/app/execute_test.py
+++ b/tests/app/execute_test.py
@@ -20,7 +20,7 @@ async def test_hello_world(http_server_client, base_url):
     assert 'test_template.css' not in html_text, "test_template should not be the default"
 
 
-async def test_no_execute_allowed(voila_app, app, http_server_client, base_url):
+async def test_no_execute_allowed(voila_app, app, http_server_client, base_url, http_server_port):
     assert voila_app.app is app
     response = (await http_server_client.fetch(base_url)).body.decode('utf-8')
     pattern = r"""kernelId": ["']([0-9a-zA-Z-]+)["']"""
@@ -28,9 +28,7 @@ async def test_no_execute_allowed(voila_app, app, http_server_client, base_url):
     kernel_id = groups[0]
     print(kernel_id, base_url)
     session_id = '445edd75-c6f5-45d2-8b58-5fe8f84a7123'
-    url = '{base_url}api/kernels/{kernel_id}/channels?session_id={session_id}'.format(
-        kernel_id=kernel_id, base_url=base_url, session_id=session_id
-    ).replace('http://', 'ws://')
+    url = f'ws://localhost:{http_server_port[1]}{base_url}api/kernels/{kernel_id}/channels?session_id={session_id}'
     conn = await tornado.websocket.websocket_connect(url)
 
     msg = {

From 441053d70a8dd994ac54c27cf4eede72799aefb7 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 16:14:24 +0200
Subject: [PATCH 14/20] Update with jupyter_server 0.3.0

---
 voila/__init__.py         |  2 +-
 voila/server_extension.py | 17 ++++++++++++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/voila/__init__.py b/voila/__init__.py
index 0cf9f3351..a24a00ff6 100644
--- a/voila/__init__.py
+++ b/voila/__init__.py
@@ -8,7 +8,7 @@
 #############################################################################
 
 from ._version import __version__  # noqa
-from .server_extension import load_jupyter_server_extension  # noqa
+from .server_extension import _load_jupyter_server_extension  # noqa
 
 
 def _jupyter_nbextension_paths():
diff --git a/voila/server_extension.py b/voila/server_extension.py
index ed740438f..2245f286d 100644
--- a/voila/server_extension.py
+++ b/voila/server_extension.py
@@ -13,8 +13,7 @@
 from jinja2 import Environment, FileSystemLoader
 
 from jupyter_server.utils import url_path_join
-from jupyter_server.base.handlers import path_regex
-from jupyter_server.base.handlers import FileFindHandler
+from jupyter_server.base.handlers import path_regex, FileFindHandler
 
 from .paths import ROOT, STATIC_ROOT, collect_template_paths, jupyter_path
 from .handler import VoilaHandler
@@ -24,7 +23,19 @@
 from .utils import get_server_root_dir
 
 
-def load_jupyter_server_extension(server_app):
+def _jupyter_server_extension_paths():
+    """
+    Returns a list of dictionaries with metadata describing
+    where to find the `_load_jupyter_server_extension` function.
+    """
+    return [
+        {
+            "module": "voila.server_extension"
+        }
+    ]
+
+
+def _load_jupyter_server_extension(server_app):
     web_app = server_app.web_app
 
     nbconvert_template_paths = []

From 1cb71e59e3b48a57d37d8fcb5531b4eef66695d0 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 16:42:46 +0200
Subject: [PATCH 15/20] Update actions/checkout

---
 .github/workflows/build.yml | 2 +-
 .github/workflows/main.yml  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index f1cdc4f19..211b6e285 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
     - name: install dependencies
       run: |
         sudo apt update
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 55f7ba384..0fb8bc87d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,7 +21,7 @@ jobs:
         python-version: [3.6, 3.7, 3.8]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
 
     - name: Add conda to $PATH
       run: echo ::add-path::$CONDA/condabin

From a2c1deadb84c17ebf9c479116ceb31653ed54de4 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Thu, 23 Apr 2020 17:34:38 +0200
Subject: [PATCH 16/20] Launch server app with AsyncMappingKernelManager

---
 tests/server/conftest.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/server/conftest.py b/tests/server/conftest.py
index e37b7e2e6..34e360663 100644
--- a/tests/server/conftest.py
+++ b/tests/server/conftest.py
@@ -23,7 +23,7 @@ def jupyter_server_args_extra():
 @pytest.fixture
 def jupyter_server_args(notebook_directory, jupyter_server_args_extra):
     debug_args = ['--ServerApp.log_level=DEBUG'] if os.environ.get('VOILA_TEST_DEBUG', False) else []
-    default_args = ['--ServerApp.token=""']
+    default_args = ['--ServerApp.token=""', '--ServerApp.kernel_manager_class=jupyter_server.services.kernels.kernelmanager.AsyncMappingKernelManager']
     return [notebook_directory] + jupyter_server_args_extra + debug_args + default_args
 
 

From 0b32611e569fd6d08dc924007125ff0e34e3146b Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Fri, 24 Apr 2020 14:49:07 +0200
Subject: [PATCH 17/20] Support AsyncMappingKernelManager and
 MappingKernelManager by forcing AsyncKernelClient

---
 tests/server/conftest.py | 2 +-
 voila/handler.py         | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/tests/server/conftest.py b/tests/server/conftest.py
index 34e360663..e37b7e2e6 100644
--- a/tests/server/conftest.py
+++ b/tests/server/conftest.py
@@ -23,7 +23,7 @@ def jupyter_server_args_extra():
 @pytest.fixture
 def jupyter_server_args(notebook_directory, jupyter_server_args_extra):
     debug_args = ['--ServerApp.log_level=DEBUG'] if os.environ.get('VOILA_TEST_DEBUG', False) else []
-    default_args = ['--ServerApp.token=""', '--ServerApp.kernel_manager_class=jupyter_server.services.kernels.kernelmanager.AsyncMappingKernelManager']
+    default_args = ['--ServerApp.token=""']
     return [notebook_directory] + jupyter_server_args_extra + debug_args + default_args
 
 
diff --git a/voila/handler.py b/voila/handler.py
index d66387600..31ca07505 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -117,6 +117,13 @@ async def _jinja_kernel_start(self, nb):
         assert not self.kernel_started, "kernel was already started"
         kernel_id = await self.kernel_manager.start_kernel(kernel_name=self.notebook.metadata.kernelspec.name, path=self.cwd)
         km = self.kernel_manager.get_kernel(kernel_id)
+        # When Voila is launched as an app, its kernel manager's type is AsyncMappingKernelManager, and thus
+        # its kernel client's type is AsyncKernelClient.
+        # But this has to be explicitly configured when launched as a server extension, with e.g.:
+        # --ServerApp.kernel_manager_class=jupyter_server.services.kernels.kernelmanager.AsyncMappingKernelManager
+        # If it's not done, the kernel manager might not be async, which is not a big deal, but we want the kernel
+        # client to be async, so we explicitly configure it for this particular case:
+        km.client_class = 'jupyter_client.asynchronous.AsyncKernelClient'
         self.executor = VoilaExecutor(nb, km=km, config=self.traitlet_config)
         self.executor.kc = km.client()
         self.executor.kc.start_channels()

From a6a793fcfacd0f3c7d4cd2187f07f208d24b7429 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Mon, 4 May 2020 16:40:21 +0200
Subject: [PATCH 18/20] Changes according to review

---
 .github/workflows/build.yml                                   | 2 +-
 .../voila/templates/default/nbconvert_templates/lab.tpl       | 2 +-
 .../voila/templates/default/nbconvert_templates/voila.tpl     | 2 +-
 voila/__init__.py                                             | 1 +
 voila/handler.py                                              | 4 ++--
 5 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 211b6e285..c26495e36 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -19,7 +19,7 @@ jobs:
     - name: install dependencies
       run: |
         sudo apt update
-        sudo apt-get install -y --no-install-recommends libgbm-dev
+        sudo apt-get install -y --no-install-recommends libgbm-dev  # see https://github.com/puppeteer/puppeteer/issues/5661
     - name: Install node
       uses: actions/setup-node@v1
       with:
diff --git a/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl b/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
index 7ea3040b8..c06cdf7d4 100644
--- a/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
+++ b/share/jupyter/voila/templates/default/nbconvert_templates/lab.tpl
@@ -1,4 +1,4 @@
-{%- extends 'display_priority.j2' -%}
+{%- extends 'display_priority.tpl' -%}
 
 {% block codecell %}
 {%- if not cell.outputs -%}
diff --git a/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl b/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
index 1e274cdfe..f9bf5409e 100644
--- a/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
+++ b/share/jupyter/voila/templates/default/nbconvert_templates/voila.tpl
@@ -62,7 +62,7 @@ a.anchor-link {
 
 {%- block body_loop -%}
   {# from this point on, the kernel is started #}
-  {%- with kernel_id = kernel_start(nb) -%}
+  {%- with kernel_id = kernel_start() -%}
     <script id="jupyter-config-data" type="application/json">
     {
         "baseUrl": "{{resources.base_url}}",
diff --git a/voila/__init__.py b/voila/__init__.py
index a24a00ff6..cbc7342ed 100644
--- a/voila/__init__.py
+++ b/voila/__init__.py
@@ -9,6 +9,7 @@
 
 from ._version import __version__  # noqa
 from .server_extension import _load_jupyter_server_extension  # noqa
+load_jupyter_server_extension = _load_jupyter_server_extension  # for backward compatibility
 
 
 def _jupyter_nbextension_paths():
diff --git a/voila/handler.py b/voila/handler.py
index 31ca07505..790764a1b 100644
--- a/voila/handler.py
+++ b/voila/handler.py
@@ -113,7 +113,7 @@ async def get(self, path=None):
     def redirect_to_file(self, path):
         self.redirect(url_path_join(self.base_url, 'voila', 'files', path))
 
-    async def _jinja_kernel_start(self, nb):
+    async def _jinja_kernel_start(self):
         assert not self.kernel_started, "kernel was already started"
         kernel_id = await self.kernel_manager.start_kernel(kernel_name=self.notebook.metadata.kernelspec.name, path=self.cwd)
         km = self.kernel_manager.get_kernel(kernel_id)
@@ -124,7 +124,7 @@ async def _jinja_kernel_start(self, nb):
         # If it's not done, the kernel manager might not be async, which is not a big deal, but we want the kernel
         # client to be async, so we explicitly configure it for this particular case:
         km.client_class = 'jupyter_client.asynchronous.AsyncKernelClient'
-        self.executor = VoilaExecutor(nb, km=km, config=self.traitlet_config)
+        self.executor = VoilaExecutor(self.notebook, km=km, config=self.traitlet_config)
         self.executor.kc = km.client()
         self.executor.kc.start_channels()
         try:

From 3506b6831c31edd35ff3fc76e47cf24d54fa5eb9 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Tue, 5 May 2020 15:33:13 +0200
Subject: [PATCH 19/20] Pass store_history to async_execute_cell()

---
 voila/execute.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/voila/execute.py b/voila/execute.py
index c0c0cac3e..177e39f34 100644
--- a/voila/execute.py
+++ b/voila/execute.py
@@ -150,9 +150,7 @@ def execute(self, nb, resources, km=None):
 
     async def execute_cell(self, cell, resources, cell_index, store_history=True):
         try:
-            # TODO: pass store_history as a 5th argument when we can require nbconver >=5.6.1
-            # result = super(VoilaExecutor, self).execute_cell(cell, resources, cell_index, store_history)
-            result = await super(VoilaExecutor, self).async_execute_cell(cell, cell_index)
+            result = await super(VoilaExecutor, self).async_execute_cell(cell, cell_index, store_history)
         except TimeoutError as e:
             self.log.error(e)
             self.show_code_cell_timeout(cell)

From 6b55fe64828429a0c8bbe220d4b1be226efa2769 Mon Sep 17 00:00:00 2001
From: David Brochart <david.brochart@gmail.com>
Date: Tue, 5 May 2020 16:25:56 +0200
Subject: [PATCH 20/20] Add comment for jinja async template execution

---
 voila/exporter.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/voila/exporter.py b/voila/exporter.py
index 09ba269df..acc12e4fc 100644
--- a/voila/exporter.py
+++ b/voila/exporter.py
@@ -104,6 +104,7 @@ async def generate_from_notebook_node(self, nb, resources=None, extra_context={}
 
     @property
     def environment(self):
+        # enable Jinja async template execution
         self.enable_async = True
         env = super(type(self), self).environment
         if 'jinja2.ext.do' not in env.extensions: