From 7b56472b77a7cb0705ed15dde11fd4cc0d32e495 Mon Sep 17 00:00:00 2001
From: Ilya Sherstyuk <isherstyuk@nvidia.com>
Date: Thu, 12 Jan 2023 18:16:58 -0800
Subject: [PATCH] Fix Exception in OutStream.close()

This bug fixes an Exception which was thrown
in OutStream.close() whenever the OutStream was
constructed with watchfd=False.

A regression test was also added to test_io.py.
---
 ipykernel/iostream.py      | 3 ++-
 ipykernel/tests/test_io.py | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/ipykernel/iostream.py b/ipykernel/iostream.py
index 92df61aea..32829f6bd 100644
--- a/ipykernel/iostream.py
+++ b/ipykernel/iostream.py
@@ -401,6 +401,7 @@ def __init__(
         self._buffer = StringIO()
         self.echo = None
         self._isatty = bool(isatty)
+        self._should_watch = False
 
         if (
             watchfd
@@ -449,7 +450,7 @@ def set_parent(self, parent):
 
     def close(self):
         """Close the stream."""
-        if sys.platform.startswith("linux") or sys.platform.startswith("darwin"):
+        if self._should_watch:
             self._should_watch = False
             self.watch_fd_thread.join()
         if self._exc:
diff --git a/ipykernel/tests/test_io.py b/ipykernel/tests/test_io.py
index f7fc8b3f4..221af1f8b 100644
--- a/ipykernel/tests/test_io.py
+++ b/ipykernel/tests/test_io.py
@@ -98,6 +98,9 @@ def test_outstream():
         stream = OutStream(session, pub, "stdout")
         stream = OutStream(session, thread, "stdout", pipe=object())
 
+        stream = OutStream(session, thread, "stdout", watchfd=False)
+        stream.close()
+
     stream = OutStream(session, thread, "stdout", isatty=True, echo=io.StringIO())
     with pytest.raises(io.UnsupportedOperation):
         stream.fileno()