Fix SignalConnector._has_already_handler check for callable type

CHANGELOG.md

@@ -121,6 +121,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `CombinedLoader` and `max_size_cycle` didn't receive a `DistributedSampler` ([#10374](https://github.com/PyTorchLightning/pytorch-lightning/issues/10374))
 
 
+- Fixed `SignalConnector._has_already_handler` check for callable type ([#10483](https://github.com/PyTorchLightning/pytorch-lightning/pull/10483))
+
+
 -
 
 

pytorch_lightning/trainer/connectors/signal_connector.py

@@ -4,7 +4,7 @@
 import sys
 from signal import Signals
 from subprocess import call
-from types import FrameType, FunctionType
+from types import FrameType
 from typing import Callable, List, Union
 
 import pytorch_lightning as pl
@@ -104,6 +104,6 @@ def _is_on_windows(self) -> bool:
 
     def _has_already_handler(self, signum: Signals) -> bool:
         try:
-            return isinstance(signal.getsignal(signum), FunctionType)
+            return callable(signal.getsignal(signum))
         except AttributeError:
             return False

tests/trainer/connectors/test_signal_connector.py

@@ -19,6 +19,7 @@
 import pytest
 
 from pytorch_lightning import Trainer
+from pytorch_lightning.trainer.connectors.signal_connector import SignalConnector
 from pytorch_lightning.utilities.exceptions import ExitGracefullyException
 from tests.helpers import BoringModel
 from tests.helpers.runif import RunIf
@@ -57,3 +58,28 @@ def training_step(self, batch, batch_idx):
         else:
             trainer.fit(model)
         assert trainer._terminate_gracefully == (False if register_handler else terminate_gracefully)
+
+
+def signal_handler():
+    pass
+
+
+class SignalHandlers:
+    def signal_handler(self):
+        pass
+
+
+@pytest.mark.parametrize(
+    ["handler", "expected_return"],
+    [
+        (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."""
+    trainer = Trainer()
+    connector = SignalConnector(trainer)
+    with mock.patch("signal.getsignal", return_value=handler):
+        assert connector._has_already_handler(signal.SIGTERM) is expected_return