gh-150818: Speed up logging.getLogger() for existing loggers

gaborbernat · gaborbernat · commit 9c0df9630a28 · 2026-06-02T16:44:53.000-07:00
getLogger() took the logging lock on every call, including the common case of
an already-registered logger. Return that logger through a lock-free fast path
backed by an atomic dict lookup. First-time creation, placeholder resolution
and parent/child wiring still run under the lock, and the fast path is safe
under both the GIL and free threading.
diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
@@ -1373,9 +1373,17 @@ def getLogger(self, name):
         logger and fix up the parent/child references which pointed to the
         placeholder to now point to the logger.
         """
-        rv = None
         if not isinstance(name, str):
             raise TypeError('A logger name must be a string')
+        # Fast path: an already-registered, non-placeholder logger can be
+        # returned without taking the lock. dict.get() is atomic under both
+        # the GIL and free threading, and a Logger is fully initialised before
+        # being inserted into loggerDict under the lock, so this never sees a
+        # partially-constructed object.
+        rv = self.loggerDict.get(name)
+        if rv is not None and not isinstance(rv, PlaceHolder):
+            return rv
+        rv = None
         with _lock:
             if name in self.loggerDict:
                 rv = self.loggerDict[name]
diff --git a/Misc/NEWS.d/next/Library/2026-06-02-15-44-58.gh-issue-150818.Orcefu.rst b/Misc/NEWS.d/next/Library/2026-06-02-15-44-58.gh-issue-150818.Orcefu.rst
@@ -0,0 +1,3 @@
+Speed up :func:`logging.getLogger` with a lock-free fast path that returns an
+already-registered logger without acquiring the logging lock. Patch by Bernát
+Gábor.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Speed up :func:`logging.getLogger` with a lock-free fast path that returns an
	`2`	`+already-registered logger without acquiring the logging lock. Patch by Bernát`
	`3`	`+Gábor.`