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https://github.com/rails/rails/commit/60fc40ea58de8b6faf98081d659e7f5b232aa25e
From 60fc40ea58de8b6faf98081d659e7f5b232aa25e Mon Sep 17 00:00:00 2001
From: Jonathan Hefner <jonathan@hefner.pro>
Date: Thu, 22 Jul 2021 13:45:57 -0500
Subject: [PATCH] Isolate descendants garbage collection test
This prevents the test from being affected by Ruby-internal thread
locals set by other tests.
Example failure: https://buildkite.com/rails/rails/builds/79505#cb261462-8e40-4adc-99fc-81708a473cc6/1076-1085
Co-authored-by: Jean Boussier <jean.boussier@gmail.com>
--- a/test/descendants_tracker_test_cases.rb
+++ b/test/descendants_tracker_test_cases.rb
@@ -28,11 +28,23 @@ def test_descendants
end
def test_descendants_with_garbage_collected_classes
- 1.times do
+ # The Ruby GC (and most other GCs for that matter) are not fully precise.
+ # When GC is run, the whole stack is scanned to mark any object reference
+ # in registers. But some of these references might simply be leftovers from
+ # previous method calls waiting to be overridden, and there's no definite
+ # way to clear them. By executing this code in a distinct thread, we ensure
+ # that such references are on a stack that will be entirely garbage
+ # collected, effectively working around the problem.
+ Thread.new do
child_klass = Class.new(Parent)
assert_equal_sets [Child1, Grandchild1, Grandchild2, Child2, child_klass], Parent.descendants
+ end.join
+
+ # Calling `GC.start` 4 times should trigger a full GC run
+ 4.times do
+ GC.start
end
- GC.start
+
assert_equal_sets [Child1, Grandchild1, Grandchild2, Child2], Parent.descendants
end
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