From e8af64eafc943906368293bb51933fcf26bd2dd3 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 5 Nov 2026 16:46:38 +0000
Subject: [PATCH] tests: Comment on self.addCleanup ordering

---
 tests/metrics/test_thread_cpu.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/metrics/test_thread_cpu.py b/tests/metrics/test_thread_cpu.py
index 1ac3d50173..a35f8550a5 100644
--- a/tests/metrics/test_thread_cpu.py
+++ b/tests/metrics/test_thread_cpu.py
@@ -91,8 +91,12 @@ class ThreadCPUMetricsTestCase(unittest.TestCase):
         # 3.14 onwards.
         thread = threading.Thread(target=run_on_thread, name="a) b) (c")
         thread.start()
+
+        # Cleanup functions are run in reverse order, so first we set the
+        # release event (to wake the thread up), and then we wait for it exit.
         self.addCleanup(thread.join)
         self.addCleanup(release.set)
+
         metrics.register_thread("test-thread", thread)
 
         # Wait for the separate thread to burn CPU before continuing.