bpo-44895: libregrtest: refleak check clears types later

[vstinner]

libregrtest now clears the type cache later to reduce the risk of
false alarm when checking for reference leaks. Previously, the type
cache was cleared too early and libregrtest raised a false alarm
about reference leaks under very specific conditions.

Move also support.gc_collect() outside clear/cleanup functions to
make the garbage collection more explicit.

Co-Authored-By: Irit Katriel [email protected]

https://bugs.python.org/issue44895

[vstinner]

@iritkatriel: Would you mind to check if this change fix https://bugs.python.org/issue44895 for you? It seems like you are the only one able to reproduce https://bugs.python.org/issue44895 :-)

[iritkatriel]

checking!

[iritkatriel]

Yeah!

[vstinner]

Using the following patch:

diff --git a/Lib/test/libregrtest/refleak.py b/Lib/test/libregrtest/refleak.py
index 096b5381cd..b82f0e6aaa 100644
--- a/Lib/test/libregrtest/refleak.py
+++ b/Lib/test/libregrtest/refleak.py
@@ -126,7 +126,7 @@ def check_rc_deltas(deltas):
         #
         #   [5, 5, 6]
         #   [10, 1, 1]
-        return all(delta >= 1 for delta in deltas)
+        return any(delta >= 1 for delta in deltas)
 
     def check_fd_deltas(deltas):
         return any(deltas)

I reproduce the bug using refleak.py attached to https://bugs.python.org/issue44895:

$ git switch main
$ git apply patch
$ ./python refleak.py 
-- 1 --
beginning 6 repetitions
123456
......
test leaked [-4, 4, -4] references, sum=-4
test leaked [-4, 4, -4] memory blocks, sum=-4

With this PR, refleak.py runs forever:

$ git switch refleak   # This PR
$ git apply patch
$ ./python refleak.py 
(...)
-- 143 --
beginning 6 repetitions
123456
......
-- 144 --
beginning 6 repetitions
123456
......
(...)