[Fix] AppLauncher: leave SIGSEGV/SIGABRT dispositions untouched

CONTRIBUTORS.md

@@ -86,6 +86,7 @@ Guidelines for modifications:
 * Diego Ferigo
 * Dongxuan Fan
 * Dorsa Rohani
+* Dundy Pasupuleti
 * Ege Sekkin
 * Emily Sturman
 * Emmanuel Ferdman

source/isaaclab/changelog.d/fix-applauncher-fatal-signal-defaults.rst

@@ -0,0 +1,6 @@
+Fixed
+^^^^^
+
+* Fixed :class:`~isaaclab.app.AppLauncher` registering a Python handler for
+  ``SIGABRT``. fatal-signal dispositions are left untouched (default or
+  carb's crash handler); graceful shutdown remains on ``SIGTERM`` only.

source/isaaclab/isaaclab/app/app_launcher.py

@@ -1535,15 +1535,18 @@ class _SimulationAppLifecycle:
 
         * Normal exit: the ``atexit`` hook closes the app once; a pending unhandled
           exception turns into exit code 1.
-        * ``SIGTERM`` / ``kill -ABRT``: ``close(exit_code=128 + signum)`` — full
-          teardown before exiting on isaacsim.simulation_app >= 2.18.5, truthful
-          status either way; if ``close()`` returns (fast shutdown disabled),
-          re-raise the signal with the default action.
+        * ``SIGTERM``: ``close(exit_code=128 + signum)``; full teardown before
+          exiting on isaacsim.simulation_app >= 2.18.5, truthful status either way;
+          if ``close()`` returns (fast shutdown disabled), re-raise the signal with
+          the default action.
         * Signal during a running close: fall back to the default action instead of
           re-entering ``close()``, which previously recursed until stack overflow.
-        * ``SIGSEGV``: not intercepted — a Python handler cannot run for main-thread
-          faults, reports success for worker-thread faults, and suppresses the carb
-          crash reporter's minidumps.
+        * ``SIGSEGV`` / ``SIGABRT``: not intercepted; dispositions are left
+          untouched (default or carb's crash handler). a python ``SIGSEGV``
+          handler that returns re-faults forever and suppresses carb crash
+          minidumps. the former ``SIGABRT`` handler restored ``SIG_DFL`` and
+          re-raised, so skipping registration leaves abort to the existing
+          disposition instead of a graceful-teardown path.
         * ``SIGINT``: Python's default handler, so Ctrl-C unwinds user code and
           exits nonzero.
 
@@ -1579,8 +1582,11 @@ def install_exit_handlers(self):
             # close on normal exit so Kit shuts down cleanly instead of via __del__
             atexit.register(self._close_at_exit)
             signal.signal(signal.SIGTERM, self._on_abort_signal)
-            signal.signal(signal.SIGABRT, self._on_abort_signal)
-            # no SIGSEGV handler and default SIGINT — see the class docstring
+            # leave SIGSEGV/SIGABRT untouched (default or carb's crash handler);
+            # skipping signal.signal does not install SIG_DFL. a python SIGSEGV
+            # handler that returns re-executes the fault forever; the former
+            # SIGABRT handler restored SIG_DFL and re-raised.
+            # restore default SIGINT so ctrl-c unwinds user code; see the class docstring
             signal.signal(signal.SIGINT, signal.default_int_handler)
 
         def _close_at_exit(self):
@@ -1593,7 +1599,7 @@ def _close_at_exit(self):
                 self._close_app(exit_code)
 
         def _on_abort_signal(self, signum, frame):
-            """Handle SIGTERM/SIGABRT: close the app once, then die by the signal."""
+            """Handle SIGTERM: close the app once, then die by the signal."""
             if self._closing:
                 signal.signal(signum, signal.SIG_DFL)
                 signal.raise_signal(signum)

source/isaaclab/test/app/test_simulation_app_lifecycle.py

@@ -160,3 +160,36 @@ def _close():  # simulates a SimulationApp.close() without the exit_code paramet
 
     assert calls == [1]
     assert "does not accept exit_code" in capfd.readouterr().err
+
+
+def test_install_exit_handlers_leaves_fatal_signals_at_default(monkeypatch):
+    """AppLauncher must not register SIGSEGV or SIGABRT; only SIGTERM gets a custom handler.
+
+    Regression for issue #7774: skipping signal.signal leaves those dispositions
+    untouched (default or carb's crash handler) rather than establishing SIG_DFL.
+    a python SIGSEGV handler that returns re-faults forever with no core dump;
+    the former SIGABRT handler restored SIG_DFL and re-raised. graceful teardown
+    stays on SIGTERM only.
+    """
+    actions = _capture_signal_actions(monkeypatch)
+    lifecycle = _make_lifecycle(lambda exit_code=0: None)
+    monkeypatch.setattr(
+        "isaaclab.app.app_launcher.atexit.register",
+        lambda callback: actions.append(("atexit", callback)),
+    )
+
+    lifecycle.install_exit_handlers()
+
+    registered = {
+        signum: handler
+        for action in actions
+        if action[0] == "set_handler"
+        for _, signum, handler in (action,)
+    }
+    assert signal.SIGTERM in registered
+    assert registered[signal.SIGTERM] == lifecycle._on_abort_signal
+    assert signal.SIGSEGV not in registered
+    assert signal.SIGABRT not in registered
+    assert registered.get(signal.SIGINT) == signal.default_int_handler
+    assert any(action[0] == "atexit" for action in actions)
+