From 02ccf8153565e0f4234f4f6cf0daf769c68094a0 Mon Sep 17 00:00:00 2001
From: zdevito <zdevito@meta.com>
Date: Fri, 31 Oct 2025 15:29:58 -0700
Subject: [PATCH] [Logging] put the actor name in the python logger

Differential Revision: [D85994688](https://our.internmc.facebook.com/intern/diff/D85994688/)

**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D85994688/)!

[ghstack-poisoned]
---
 python/monarch/_src/actor/actor_mesh.py | 45 ++++++++++++++++++++++---
 python/tests/test_python_actors.py      | 32 +++++++++++++++++-
 2 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/python/monarch/_src/actor/actor_mesh.py b/python/monarch/_src/actor/actor_mesh.py
index 2b15d48a8..5ee5532bf 100644
--- a/python/monarch/_src/actor/actor_mesh.py
+++ b/python/monarch/_src/actor/actor_mesh.py
@@ -17,6 +17,8 @@
 from abc import abstractproperty
 
 from dataclasses import dataclass
+
+from functools import cache
 from pprint import pformat
 from textwrap import indent
 from traceback import TracebackException
@@ -257,6 +259,41 @@ def _root_client_context() -> "Context": ...
     "monarch.actor_mesh._context"
 )
 
+
+class _ActorFilter(logging.Filter):
+    def __init__(self) -> None:
+        super().__init__()
+
+    def filter(self, record: Any) -> bool:
+        ctx = _context.get(None)
+        if ctx is not None:
+            record.msg = f"[actor={ctx.actor_instance}] {record.msg}"
+        return True
+
+
+@cache
+def _init_context_log_handler() -> None:
+    af: _ActorFilter = _ActorFilter()
+    logger = logging.getLogger()
+    for handler in logger.handlers:
+        handler.addFilter(af)
+
+    _original_addHandler: Any = logging.Logger.addHandler
+
+    def _patched_addHandler(self: Any, handler: Any) -> None:
+        _original_addHandler(self, handler)
+        if af not in handler.filters:
+            handler.addFilter(af)
+
+    # typing: ignore
+    logging.Logger.addHandler = _patched_addHandler
+
+
+def _set_context(c: Context) -> None:
+    _init_context_log_handler()
+    _context.set(c)
+
+
 T = TypeVar("T")
 
 
@@ -305,7 +342,7 @@ def context() -> Context:
     c = _context.get(None)
     if c is None:
         c = Context._root_client_context()
-        _context.set(c)
+        _set_context(c)
 
         from monarch._src.actor.host_mesh import create_local_host_mesh
         from monarch._src.actor.proc_mesh import _get_controller_controller
@@ -919,7 +956,7 @@ async def handle(
         # response_port can be None. If so, then sending to port will drop the response,
         # and raise any exceptions to the caller.
         try:
-            _context.set(ctx)
+            _set_context(ctx)
 
             DebugContext.set(DebugContext())
 
@@ -1053,7 +1090,7 @@ def _post_mortem_debug(self, exc_tb: Any) -> None:
     def _handle_undeliverable_message(
         self, cx: Context, message: UndeliverableMessageEnvelope
     ) -> bool:
-        _context.set(cx)
+        _set_context(cx)
         handle_undeliverable = getattr(
             self.instance, "_handle_undeliverable_message", None
         )
@@ -1063,7 +1100,7 @@ def _handle_undeliverable_message(
             return False
 
     def __supervise__(self, cx: Context, *args: Any, **kwargs: Any) -> object:
-        _context.set(cx)
+        _set_context(cx)
         instance = self.instance
         if instance is None:
             # This could happen because of the following reasons. Both
diff --git a/python/tests/test_python_actors.py b/python/tests/test_python_actors.py
index 287dcd8af..1b1b3b8f2 100644
--- a/python/tests/test_python_actors.py
+++ b/python/tests/test_python_actors.py
@@ -9,6 +9,7 @@
 import asyncio
 import ctypes
 import importlib.resources
+import io
 import logging
 import operator
 import os
@@ -20,6 +21,7 @@
 import time
 import unittest
 import unittest.mock
+from contextlib import contextmanager
 from tempfile import TemporaryDirectory
 from types import ModuleType
 from typing import cast, Tuple
@@ -68,7 +70,6 @@
 from monarch.tools.config import defaults
 from typing_extensions import assert_type
 
-
 needs_cuda = pytest.mark.skipif(
     not torch.cuda.is_available(),
     reason="CUDA not available",
@@ -1688,9 +1689,34 @@ def test_login_job():
         j.kill()
 
 
+class CaptureLogs:
+    def __init__(self):
+        log_stream = io.StringIO()
+        handler = logging.StreamHandler(log_stream)
+        handler.setFormatter(logging.Formatter("%(message)s"))
+
+        logger = logging.getLogger("capture")
+        logger.setLevel(logging.INFO)
+        logger.addHandler(handler)
+
+        self.log_stream = log_stream
+        self.logger = logger
+
+    @property
+    def contents(self) -> str:
+        return self.log_stream.getvalue()
+
+
 class Named(Actor):
     @endpoint
     def report(self):
+        logs = CaptureLogs()
+        logs.logger.error("HUH")
+        assert (
+            "actor=<root>.<tests.test_python_actors.Named the_name{'f': 0/2}>"
+            in logs.contents
+        )
+
         return context().actor_instance.creator, str(context().actor_instance)
 
 
@@ -1706,3 +1732,7 @@ def test_instance_name():
     assert result == "<root>.<tests.test_python_actors.Named the_name{'f': 0/2}>"
     assert cr.name == "root"
     assert str(context().actor_instance) == "<root>"
+
+    logs = CaptureLogs()
+    logs.logger.error("HUH")
+    assert "actor=<root>" in logs.contents