Fix _storage_main terminate_on_parent_death not working on mac

Prior to this commit, the `terminate_on_parent_death` function was only usable on linux, due to it using the prctl command.
This commit creates a new thread which polls the parent process, and signals terminate when it can no longer find the parent.

src/ert/services/_storage_main.py

@@ -7,7 +7,8 @@
 import signal
 import socket
 import string
-import sys
+import threading
+import time
 import warnings
 from typing import Any, Dict, List, Optional, Union
 
@@ -123,30 +124,23 @@ def run_server(args: Optional[argparse.Namespace] = None, debug: bool = False) -
         server.run(sockets=[sock])
 
 
-def terminate_on_parent_death() -> None:
-    """Quit the server when the parent does a SIGABRT or is otherwise destroyed.
-    This functionality has existed on Linux for a good while, but it isn't
-    exposed in the Python standard library. Use ctypes to hook into the
-    functionality.
+def terminate_on_parent_death(
+    stopped: threading.Event, poll_interval: float = 1.0
+) -> None:
+    """
+    Quit the server when the parent process is no longer running.
     """
-    if sys.platform != "linux" or "ERT_COMM_FD" not in os.environ:
-        return
-
-    from ctypes import CDLL, c_int, c_ulong  # noqa: PLC0415
-
-    lib = CDLL(None)
 
-    # from <sys/prctl.h>
-    # int prctl(int option, ...)
-    prctl = lib.prctl
-    prctl.restype = c_int
-    prctl.argtypes = (c_int, c_ulong)
+    def check_parent_alive() -> bool:
+        return os.getppid() != 1
 
-    # from <linux/prctl.h>
-    PR_SET_PDEATHSIG = 1
+    while check_parent_alive():
+        if stopped.is_set():
+            return
+        time.sleep(poll_interval)
 
-    # connect parent death signal to our SIGTERM
-    prctl(PR_SET_PDEATHSIG, signal.SIGTERM)
+    # Parent is no longer alive, terminate this process.
+    os.kill(os.getpid(), signal.SIGTERM)
 
 
 if __name__ == "__main__":
@@ -156,6 +150,14 @@ def terminate_on_parent_death() -> None:
     warnings.filterwarnings("ignore", category=DeprecationWarning)
     uvicorn.config.LOGGING_CONFIG.clear()
     uvicorn.config.LOGGING_CONFIG.update(logging_conf)
-    terminate_on_parent_death()
+    _stopped = threading.Event()
+    terminate_on_parent_death_thread = threading.Thread(
+        target=terminate_on_parent_death, args=[_stopped, 1.0]
+    )
     with ErtPluginContext(logger=logging.getLogger()) as context:
-        run_server(debug=False)
+        terminate_on_parent_death_thread.start()
+        try:
+            run_server(debug=False)
+        finally:
+            _stopped.set()
+            terminate_on_parent_death_thread.join()

tests/ert/ui_tests/cli/test_cli.py

@@ -1,3 +1,4 @@
+import asyncio
 import fileinput
 import json
 import logging
@@ -13,6 +14,7 @@
 import pytest
 import websockets.exceptions
 import xtgeo
+from psutil import NoSuchProcess, Process, ZombieProcess
 from resdata.summary import Summary
 
 import _ert.threading
@@ -955,3 +957,41 @@ def raise_connection_error(*args, **kwargs):
             ENSEMBLE_EXPERIMENT_MODE,
             "poly.ert",
         )
+
+
+@pytest.mark.usefixtures("copy_poly_case")
+async def test_that_killed_ert_does_not_leave_storage_server_process():
+    ert_subprocess = await asyncio.create_subprocess_exec("ert", "gui", "poly.ert")
+    assert ert_subprocess.returncode is None
+    ert_process = Process(ert_subprocess.pid)
+
+    async def _find_storage_process_pid() -> int:
+        while True:
+            for ert_child_process in ert_process.children():
+                try:
+                    if "_storage_main" in ert_child_process.cmdline()[1]:
+                        return ert_child_process.pid
+                except (ZombieProcess, NoSuchProcess, IndexError):
+                    pass
+            await asyncio.sleep(0.10)
+
+    storage_process_pid = await asyncio.wait_for(
+        _find_storage_process_pid(), timeout=30
+    )
+
+    assert ert_subprocess.returncode is None
+    ert_subprocess.kill()
+    await ert_subprocess.wait()
+    assert ert_subprocess.returncode is not None
+
+    storage_process = Process(storage_process_pid)
+
+    async def _wait_for_storage_process_to_shut_down():
+        storage_server_has_shutdown = asyncio.Event()
+        while not storage_server_has_shutdown.is_set():
+            if not storage_process.is_running():
+                storage_server_has_shutdown.set()
+            await asyncio.sleep(0.1)
+
+    await asyncio.wait_for(_wait_for_storage_process_to_shut_down(), timeout=15)
+    assert not storage_process.is_running()