Fix `HomeServer`s leaking during `trial` test runs (#15630)

This change fixes two memory leaks during `trial` test runs.

Garbage collection is disabled during each test case and a gen-0 GC is
run at the end of each test. However, when the gen-0 GC is run, the
`TestCase` object usually still holds references to the `HomeServer`
used during the test. As a result, the `HomeServer` gets promoted to
gen-1 and then never garbage collected.

Fix this by periodically running full GCs.

Additionally, fix `HomeServer`s leaking after tests that touch inbound
federation due to `FederationRateLimiter`s adding themselves to a global
set, by turning the set into a `WeakSet`.

Resolves #15622.

Signed-off-by: Sean Quah <seanq@matrix.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/tests/unittest.py b/tests/unittest.py
index b6fdf69635..623c5a75a2 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -229,13 +229,20 @@ class TestCase(unittest.TestCase):
         #
         # The easiest way to do this would be to do a full GC after each test
         # run, but that is very expensive. Instead, we disable GC (above) for
-        # the duration of the test so that we only need to run a gen-0 GC, which
-        # is a lot quicker.
+        # the duration of the test and only run a gen-0 GC, which is a lot
+        # quicker. This doesn't clean up everything, since the TestCase
+        # instance still holds references to objects created during the test,
+        # such as HomeServers, so we do a full GC every so often.
 
         @around(self)
         def tearDown(orig: Callable[[], R]) -> R:
             ret = orig()
             gc.collect(0)
+            # Run a full GC every 50 gen-0 GCs.
+            gen0_stats = gc.get_stats()[0]
+            gen0_collections = gen0_stats["collections"]
+            if gen0_collections % 50 == 0:
+                gc.collect()
             gc.enable()
             set_current_context(SENTINEL_CONTEXT)