From edec0b93cabbe5e03d658a2aa4c2c1b79cf8e85e Mon Sep 17 00:00:00 2001
From: Erik Johnston <erikj@matrix.org>
Date: Fri, 15 Sep 2023 09:10:24 +0100
Subject: [PATCH] Only use literal strings for process names (#16315)

---
 changelog.d/16315.misc                        |  1 +
 synapse/appservice/scheduler.py               | 13 ++++---------
 synapse/metrics/background_process_metrics.py |  7 +++++--
 synapse/util/caches/expiringcache.py          |  4 +---
 4 files changed, 11 insertions(+), 14 deletions(-)
 create mode 100644 changelog.d/16315.misc

diff --git a/changelog.d/16315.misc b/changelog.d/16315.misc
new file mode 100644
index 0000000000..d88782c979
--- /dev/null
+++ b/changelog.d/16315.misc
@@ -0,0 +1 @@
+Only use literal strings for background process names.
diff --git a/synapse/appservice/scheduler.py b/synapse/appservice/scheduler.py
index 3a319b0d42..79f95f7653 100644
--- a/synapse/appservice/scheduler.py
+++ b/synapse/appservice/scheduler.py
@@ -200,9 +200,7 @@ class _ServiceQueuer:
         if service.id in self.requests_in_flight:
             return
 
-        run_as_background_process(
-            "as-sender-%s" % (service.id,), self._send_request, service
-        )
+        run_as_background_process("as-sender", self._send_request, service)
 
     async def _send_request(self, service: ApplicationService) -> None:
         # sanity-check: we shouldn't get here if this service already has a sender
@@ -478,14 +476,11 @@ class _Recoverer:
         self.backoff_counter = 1
 
     def recover(self) -> None:
-        def _retry() -> None:
-            run_as_background_process(
-                "as-recoverer-%s" % (self.service.id,), self.retry
-            )
-
         delay = 2**self.backoff_counter
         logger.info("Scheduling retries on %s in %fs", self.service.id, delay)
-        self.clock.call_later(delay, _retry)
+        self.clock.call_later(
+            delay, run_as_background_process, "as-recoverer", self.retry
+        )
 
     def _backoff(self) -> None:
         # cap the backoff to be around 8.5min => (2^9) = 512 secs
diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py
index f1f1f0cdf9..fceb7a9f3c 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -48,6 +48,9 @@ from synapse.metrics._types import Collector
 if TYPE_CHECKING:
     import resource
 
+    # Old versions don't have `LiteralString`
+    from typing_extensions import LiteralString
+
 
 logger = logging.getLogger(__name__)
 
@@ -191,7 +194,7 @@ R = TypeVar("R")
 
 
 def run_as_background_process(
-    desc: str,
+    desc: "LiteralString",
     func: Callable[..., Awaitable[Optional[R]]],
     *args: Any,
     bg_start_span: bool = True,
@@ -259,7 +262,7 @@ P = ParamSpec("P")
 
 
 def wrap_as_background_process(
-    desc: str,
+    desc: "LiteralString",
 ) -> Callable[
     [Callable[P, Awaitable[Optional[R]]]],
     Callable[P, "defer.Deferred[Optional[R]]"],
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index 8e4c34039d..e73cf66080 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -84,9 +84,7 @@ class ExpiringCache(Generic[KT, VT]):
             return
 
         def f() -> "defer.Deferred[None]":
-            return run_as_background_process(
-                "prune_cache_%s" % self._cache_name, self._prune_cache
-            )
+            return run_as_background_process("prune_cache", self._prune_cache)
 
         self._clock.looping_call(f, self._expiry_ms / 2)