From 7516811315c76321e847cf28955937195c577d2f Mon Sep 17 00:00:00 2001
From: Bobby Impollonia <bobbyi@gmail.com>
Date: Mon, 13 Dec 2021 12:45:33 -0500
Subject: [PATCH] fix(setup_helpers): ensure ThreadPool is closed (#3548)

* Ensure ThreadPool is closed in setup_helpers

The ParallelCompile setup helper using a ThreadPool to enable its
parallelism. It does not properly close the pool when it is done with
it.
This can lead to a "Exception ignored in: <function Pool.__del__..."
message with traceback being printed at shutdown.
Use pool.terminate() instead of context manager for Python 2.7
compatibility

* Add note to remove code that supports Python 2

Co-authored-by: Bobby Impollonia <bobby@k13capital.com>
---
 pybind11/setup_helpers.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/pybind11/setup_helpers.py b/pybind11/setup_helpers.py
index d6d84f67..5b7c9aab 100644
--- a/pybind11/setup_helpers.py
+++ b/pybind11/setup_helpers.py
@@ -466,8 +466,14 @@ class ParallelCompile(object):
                     threads = 1
 
             if threads > 1:
-                for _ in ThreadPool(threads).imap_unordered(_single_compile, objects):
-                    pass
+                pool = ThreadPool(threads)
+                # In Python 2, ThreadPool can't be used as a context manager.
+                # Once we are no longer supporting it, this can be 'with pool:'
+                try:
+                    for _ in pool.imap_unordered(_single_compile, objects):
+                        pass
+                finally:
+                    pool.terminate()
             else:
                 for ob in objects:
                     _single_compile(ob)