From cce8520efb09517211ea2c6aeb426d4a65bafa67 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <7190048+kegsay@users.noreply.github.com>
Date: Thu, 19 Mar 2026 13:45:28 +0000
Subject: [PATCH] Do not do opentracing wrapping if tracing is disabled

This shows up in profiles as wasted CPU time.
---
 synapse/logging/opentracing.py     | 9 +++++++++
 synapse/util/caches/descriptors.py | 6 ++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/synapse/logging/opentracing.py b/synapse/logging/opentracing.py
index 6e4e029163..3037097cb2 100644
--- a/synapse/logging/opentracing.py
+++ b/synapse/logging/opentracing.py
@@ -943,6 +943,10 @@ def _custom_sync_async_decorator(
         async def _wrapper(
             *args: P.args, **kwargs: P.kwargs
         ) -> Any:  # Return type is RInner
+            # Short-circuit: if opentracing was disabled after decoration time
+            # (init_tracer sets opentracing=None), skip all wrapping overhead.
+            if opentracing is None:
+                return await func(*args, **kwargs)  # type: ignore[unreachable]
             # type-ignore: func() returns R, but mypy doesn't know that R is
             # Awaitable here.
             with wrapping_logic(func, *args, **kwargs):  # type: ignore[arg-type]
@@ -953,6 +957,11 @@ def _custom_sync_async_decorator(
         # `@defer.inlineCallbacks` or that return a `Deferred` or other `Awaitable`.
         @wraps(func)
         def _wrapper(*args: P.args, **kwargs: P.kwargs) -> Any:
+            # Short-circuit: if opentracing was disabled after decoration time
+            # (init_tracer sets opentracing=None), skip all wrapping overhead.
+            if opentracing is None:
+                return func(*args, **kwargs)  # type: ignore[unreachable]
+
             scope = wrapping_logic(func, *args, **kwargs)
             scope.__enter__()
 
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 48c8f8f043..d416ca97ac 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -455,9 +455,7 @@ class DeferredCacheListDescriptor(_CacheDescriptorBase):
                     cache_entry.error_bulk(cache, missing, f)
 
                 args_to_call = dict(arg_dict)
-                args_to_call[list_name] = {
-                    cache_key_to_arg(key) for key in missing
-                }
+                args_to_call[list_name] = {cache_key_to_arg(key) for key in missing}
 
                 # dispatch the call, and attach the two handlers
                 missing_d = defer.maybeDeferred(
@@ -710,4 +708,4 @@ def _get_cache_key_gen(
             pos += 1
         else:
             if inc:
-                yield param_defaults[nm]
\ No newline at end of file
+                yield param_defaults[nm]