fix: Handle signal registration outside the main thread

python/restate/server.py

@@ -228,7 +228,7 @@ async def app(scope: Scope, receive: Receive, send: Send):
             loop = asyncio.get_running_loop()
             try:
                 loop.add_signal_handler(signal.SIGTERM, _on_sigterm)
-            except (NotImplementedError, RuntimeError):
+            except (NotImplementedError, RuntimeError, ValueError):
                 pass  # Windows or non-main thread
             sigterm_installed = True
         try:

tests/server.py

@@ -0,0 +1,63 @@
+#
+#  Copyright (c) 2023-2025 - Restate Software, Inc., Restate GmbH
+#
+#  This file is part of the Restate SDK for Python,
+#  which is released under the MIT license.
+#
+#  You can find a copy of the license in file LICENSE in the root
+#  directory of this repository or package, or at
+#  https://github.com/restatedev/sdk-typescript/blob/main/LICENSE
+#
+import asyncio
+from unittest.mock import Mock
+
+import pytest
+
+from restate.endpoint import Endpoint
+
+
+@pytest.fixture(scope="session")
+def anyio_backend():
+    return "asyncio"
+
+
+pytestmark = [pytest.mark.anyio]
+
+
+async def test_signal_handler_rejection_does_not_fail_request(monkeypatch: pytest.MonkeyPatch):
+    loop = asyncio.get_running_loop()
+    monkeypatch.setattr(
+        loop,
+        "add_signal_handler",
+        Mock(side_effect=ValueError("add_signal_handler() can only be called from the main thread")),
+    )
+
+    app = Endpoint().app()
+    sent = []
+
+    async def receive():
+        return {"type": "http.request", "body": b"", "more_body": False}
+
+    async def send(message):
+        sent.append(message)
+
+    await app(
+        {
+            "type": "http",
+            "asgi": {"version": "3.0"},
+            "http_version": "1.1",
+            "method": "GET",
+            "scheme": "http",
+            "path": "/restate/health",
+            "raw_path": b"/restate/health",
+            "query_string": b"",
+            "headers": [],
+            "client": ("127.0.0.1", 1234),
+            "server": ("127.0.0.1", 9080),
+        },
+        receive,
+        send,
+    )
+
+    response_starts = [message for message in sent if message["type"] == "http.response.start"]
+    assert [message["status"] for message in response_starts] == [200]