Fix Windows subprocess handle issue

jupyter_server/utils.py

@@ -395,3 +395,28 @@ async def _():
         return obj
 
     return _()
+
+
+def _init_asyncio_patch():
+    if sys.platform.startswith("win"):
+        # Windows specific event-loop policy. Although WindowsSelectorEventLoop is the current
+        # default event loop prior to Python 3.8, WindowsProactorEventLoop becomes the default
+        # in Python 3.8. However, using WindowsProactorEventLoop fails during creation of
+        # IOLoopKernelClient because it doesn't implement add_reader(), while using
+        # WindowsSelectorEventLoop fails during asyncio.create_subprocess_exec() because it
+        # doesn't implement _make_subprocess_transport().  As a result, we need to force the use of
+        # the WindowsSelectorEventLoop.
+        # See https://github.com/takluyver/jupyter_kernel_mgmt/issues/31
+        # The following approach to this is from https://github.com/jupyter/notebook/pull/5047 by @minrk
+        try:
+            from asyncio import (
+                WindowsProactorEventLoopPolicy,
+                WindowsSelectorEventLoopPolicy,
+            )
+        except ImportError:
+            pass
+        else:
+            if type(asyncio.get_event_loop_policy()) is WindowsProactorEventLoopPolicy:
+                # WindowsProactorEventLoopPolicy is not compatible with tornado 6
+                # fallback to the pre-3.8 default of Selector
+                asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())

tests/services/sessions/test_api.py

@@ -7,12 +7,18 @@
 
 from nbformat.v4 import new_notebook
 from nbformat import writes
+from jupyter_server.utils import _init_asyncio_patch
 
 from ...utils import expected_http_error
 
 j = lambda r: json.loads(r.body.decode())
 
 
+@pytest.fixture
+def asyncio_patch():
+    _init_asyncio_patch()
+
+
 class SessionClient:
 
     def __init__(self, fetch_callable):
@@ -116,7 +122,7 @@ def session_client(root_dir, fetch):
     shutil.rmtree(str(subdir), ignore_errors=True)
 
 
-async def test_create(session_client):
+async def test_create(session_client, asyncio_patch):
     # Make sure no sessions exist.
     resp = await session_client.list()
     sessions = j(resp)
@@ -146,7 +152,7 @@ async def test_create(session_client):
     await session_client.cleanup()
 
 
-async def test_create_file_session(session_client):
+async def test_create_file_session(session_client, asyncio_patch):
     resp = await session_client.create('foo/nb1.py', type='file')
     assert resp.code == 201
     newsession = j(resp)
@@ -155,7 +161,7 @@ async def test_create_file_session(session_client):
     await session_client.cleanup()
 
 
-async def test_create_console_session(session_client):
+async def test_create_console_session(session_client, asyncio_patch):
     resp = await session_client.create('foo/abc123', type='console')
     assert resp.code == 201
     newsession = j(resp)
@@ -165,7 +171,7 @@ async def test_create_console_session(session_client):
     await session_client.cleanup()
 
 
-async def test_create_deprecated(session_client):
+async def test_create_deprecated(session_client, asyncio_patch):
     resp = await session_client.create_deprecated('foo/nb1.ipynb')
     assert resp.code == 201
     newsession = j(resp)
@@ -176,7 +182,7 @@ async def test_create_deprecated(session_client):
     await session_client.cleanup()
 
 
-async def test_create_with_kernel_id(session_client, fetch):
+async def test_create_with_kernel_id(session_client, fetch, asyncio_patch):
     # create a new kernel
     resp = await fetch('api/kernels', method='POST', allow_nonstandard_methods=True)
     kernel = j(resp)
@@ -201,7 +207,7 @@ async def test_create_with_kernel_id(session_client, fetch):
     # Need to find a better solution to this.
     await session_client.cleanup()
 
-async def test_delete(session_client):
+async def test_delete(session_client, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     newsession = j(resp)
     sid = newsession['id']
@@ -219,7 +225,7 @@ async def test_delete(session_client):
     # Need to find a better solution to this.
     await session_client.cleanup()
 
-async def test_modify_path(session_client):
+async def test_modify_path(session_client, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     newsession = j(resp)
     sid = newsession['id']
@@ -231,7 +237,7 @@ async def test_modify_path(session_client):
     # Need to find a better solution to this.
     await session_client.cleanup()
 
-async def test_modify_path_deprecated(session_client):
+async def test_modify_path_deprecated(session_client, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     newsession = j(resp)
     sid = newsession['id']
@@ -243,7 +249,7 @@ async def test_modify_path_deprecated(session_client):
     # Need to find a better solution to this.
     await session_client.cleanup()
 
-async def test_modify_type(session_client):
+async def test_modify_type(session_client, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     newsession = j(resp)
     sid = newsession['id']
@@ -255,7 +261,7 @@ async def test_modify_type(session_client):
     # Need to find a better solution to this.
     await session_client.cleanup()
 
-async def test_modify_kernel_name(session_client, fetch):
+async def test_modify_kernel_name(session_client, fetch, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     before = j(resp)
     sid = before['id']
@@ -277,7 +283,7 @@ async def test_modify_kernel_name(session_client, fetch):
     await session_client.cleanup()
 
 
-async def test_modify_kernel_id(session_client, fetch):
+async def test_modify_kernel_id(session_client, fetch, asyncio_patch):
     resp = await session_client.create('foo/nb1.ipynb')
     before = j(resp)
     sid = before['id']
@@ -304,4 +310,4 @@ async def test_modify_kernel_id(session_client, fetch):
     assert kernel_list == [kernel]
 
     # Need to find a better solution to this.
-    await session_client.cleanup()
+    await session_client.cleanup()