From a4385923da79570d58b769e04d073dc18b94171e Mon Sep 17 00:00:00 2001
From: Steven Silvester <steven.silvester@ieee.org>
Date: Wed, 19 Oct 2022 17:06:09 -0500
Subject: [PATCH] Defer creation of ready future (#858)

---
 jupyter_client/manager.py | 30 ++++++++++++++++--------------
 pyproject.toml            |  2 +-
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/jupyter_client/manager.py b/jupyter_client/manager.py
index 4aa18bba8..c8b062b04 100644
--- a/jupyter_client/manager.py
+++ b/jupyter_client/manager.py
@@ -54,6 +54,16 @@ class _ShutdownStatus(Enum):
 F = t.TypeVar('F', bound=t.Callable[..., t.Any])
 
 
+def _get_future() -> t.Union[Future, CFuture]:
+    """Get an appropriate Future object"""
+    try:
+        asyncio.get_running_loop()
+        return Future()
+    except RuntimeError:
+        # No event loop running, use concurrent future
+        return CFuture()
+
+
 def in_pending_state(method: F) -> F:
     """Sets the kernel to a pending state by
     creating a fresh Future for the KernelManager's `ready`
@@ -64,12 +74,8 @@ def in_pending_state(method: F) -> F:
     @functools.wraps(method)
     async def wrapper(self, *args, **kwargs):
         # Create a future for the decorated method
-        if self._attempted_start:
-            try:
-                self._ready = Future()
-            except RuntimeError:
-                # No event loop running, use concurrent future
-                self._ready = CFuture()
+        if self._attempted_start or not self._ready:
+            self._ready = _get_future()
         try:
             # call wrapped method, await, and set the result or exception.
             out = await method(self, *args, **kwargs)
@@ -91,19 +97,13 @@ class KernelManager(ConnectionFileMixin):
     This version starts kernels with Popen.
     """
 
-    _ready: t.Union[Future, CFuture]
+    _ready: t.Optional[t.Union[Future, CFuture]]
 
     def __init__(self, *args, **kwargs):
         super().__init__(**kwargs)
         self._shutdown_status = _ShutdownStatus.Unset
         self._attempted_start = False
-        # Create a place holder future.
-        try:
-            asyncio.get_running_loop()
-            self._ready = Future()
-        except RuntimeError:
-            # No event loop running, use concurrent future
-            self._ready = CFuture()
+        self._ready = None
 
     _created_context: Bool = Bool(False)
 
@@ -188,6 +188,8 @@ def _default_cache_ports(self) -> bool:
     @property
     def ready(self) -> t.Union[CFuture, Future]:
         """A future that resolves when the kernel process has started for the first time"""
+        if not self._ready:
+            self._ready = _get_future()
         return self._ready
 
     @property
diff --git a/pyproject.toml b/pyproject.toml
index df40855ac..4ffa86315 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,7 +50,7 @@ Homepage = "https://jupyter.org"
 test = [
     "codecov",
     "coverage",
-    "ipykernel>=6.5",
+    "ipykernel>=6.12",
     "ipython",
     "mypy",
     "pre-commit",