From 753cce269738e93f36136f7daaf62bf1d10c1f87 Mon Sep 17 00:00:00 2001
From: Christian Clauss <cclauss@me.com>
Date: Thu, 21 Jan 2021 13:50:36 +0100
Subject: [PATCH] cache.py: Avoid dict changed size during iteration

Subset of #4330

This code is ___only used in testing___ but it raises a RuntimeError on Apple Silicon M1 Macs.

See #4330 Screenshots, problem 4 for details.
---
 openlibrary/core/cache.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/openlibrary/core/cache.py b/openlibrary/core/cache.py
index 25636542ffa..5639ede812d 100644
--- a/openlibrary/core/cache.py
+++ b/openlibrary/core/cache.py
@@ -157,7 +157,7 @@ def join_threads(self):
 
         Used only in testing.
         """
-        for name, thread in self.active_threads.items():
+        for name, thread in list(self.active_threads.items()):
             thread.join()
 
     def encode_args(self, args, kw=None):