Fix a memory leak when running the unit tests.

changelog.d/13798.misc

@@ -0,0 +1 @@
+Fix a memory leak when running the unit tests.

synapse/util/caches/__init__.py

@@ -205,8 +205,9 @@ def register_cache(
  add_resizable_cache(cache_name, resize_callback)
 
  metric = CacheMetric(cache, cache_type, cache_name, collect_callback)
+ metric_name = "cache_%s_%s" % (cache_type, cache_name)
  caches_by_name[cache_name] = cache
- CACHE_METRIC_REGISTRY.register_hook(metric.collect)
+ CACHE_METRIC_REGISTRY.register_hook(metric_name, metric.collect)
  return metric
 
 

synapse/util/metrics.py

@@ -15,7 +15,7 @@
 import logging
 from functools import wraps
 from types import TracebackType
-from typing import Awaitable, Callable, Generator, List, Optional, Type, TypeVar
+from typing import Awaitable, Callable, Dict, Generator, Optional, Type, TypeVar
 
 from prometheus_client import CollectorRegistry, Counter, Metric
 from typing_extensions import Concatenate, ParamSpec, Protocol
@@ -220,21 +220,21 @@ class DynamicCollectorRegistry(CollectorRegistry):
 
  def __init__(self) -> None:
  super().__init__()
- self._pre_update_hooks: List[Callable[[], None]] = []
+ self._pre_update_hooks: Dict[str, Callable[[], None]] = {}
 
  def collect(self) -> Generator[Metric, None, None]:
  """
  Collects metrics, calling pre-update hooks first.
  """
 
- for pre_update_hook in self._pre_update_hooks:
+ for pre_update_hook in self._pre_update_hooks.values():
  pre_update_hook()
 
  yield from super().collect()
 
- def register_hook(self, hook: Callable[[], None]) -> None:
+ def register_hook(self, metric_name: str, hook: Callable[[], None]) -> None:
  """
  Registers a hook that is called before metric collection.
  """
 
- self._pre_update_hooks.append(hook)
+ self._pre_update_hooks[metric_name] = hook