Fix SignalConnector._has_already_handler check for callable type

CHANGELOG.md

@@ -199,6 +199,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed an issue with `SignalConnector` not restoring the default signal handlers on teardown when running on SLURM or with fault-tolerant training enabled ([#10611](https://github.com/PyTorchLightning/pytorch-lightning/pull/10611))
 
 
+- Fixed `SignalConnector._has_already_handler` check for callable type ([#10483](https://github.com/PyTorchLightning/pytorch-lightning/pull/10483))
+
+
 -  Disabled batch_size extraction for torchmetric instances because they accumulate the metrics internally ([#10815](https://github.com/PyTorchLightning/pytorch-lightning/pull/10815))
 
 

pytorch_lightning/trainer/connectors/signal_connector.py

@@ -5,7 +5,7 @@
 import threading
 from signal import Signals
 from subprocess import call
-from types import FrameType, FunctionType
+from types import FrameType
 from typing import Any, Callable, Dict, List, Set, Union
 
 import pytorch_lightning as pl
@@ -138,10 +138,7 @@ def _is_on_windows() -> bool:
 
     @staticmethod
     def _has_already_handler(signum: Signals) -> bool:
-        try:
-            return isinstance(signal.getsignal(signum), FunctionType)
-        except AttributeError:
-            return False
+        return signal.getsignal(signum) is not signal.SIG_DFL
 
     @staticmethod
     def _register_signal(signum: Signals, handlers: HandlersCompose) -> None:

tests/trainer/connectors/test_signal_connector.py

@@ -109,3 +109,27 @@ def test_signal_connector_in_thread():
     with concurrent.futures.ThreadPoolExecutor(max_workers=1) as executor:
         for future in concurrent.futures.as_completed([executor.submit(_registering_signals)]):
             assert future.exception() is None
+
+
+def signal_handler():
+    pass
+
+
+class SignalHandlers:
+    def signal_handler(self):
+        pass
+
+
+@pytest.mark.parametrize(
+    ["handler", "expected_return"],
+    [
+        (signal.Handlers.SIG_IGN, True),
+        (signal.Handlers.SIG_DFL, False),
+        (signal_handler, True),
+        (SignalHandlers().signal_handler, True),
+    ],
+)
+def test_has_already_handler(handler, expected_return):
+    """Test that the SignalConnector detects whether a signal handler is already attached."""
+    with mock.patch("pytorch_lightning.trainer.connectors.signal_connector.signal.getsignal", return_value=handler):
+        assert SignalConnector._has_already_handler(signal.SIGTERM) is expected_return