fix(process): give backend workers a parent-death safety net (#10639)

* fix(grpc): self-terminate backend workers when LocalAI dies non-gracefully

Symptom: a backend model-worker subprocess (the per-model gRPC server LocalAI
spawns) can be orphaned and linger — holding VRAM and its listen port — if the
LocalAI process is killed non-gracefully (e.g. a supervisor's graceful-shutdown
grace period elapses and LocalAI is SIGKILLed) before its own teardown runs.

Root cause: LocalAI's graceful teardown (pkg/signals/handler.go installs the
SIGINT/SIGTERM handler; core/cli/run.go registers app.Shutdown ->
ModelLoader.StopAllGRPC -> process.Stop in pkg/model/process.go) only runs when
LocalAI receives a catchable signal and survives long enough to run its
handlers. Backends are spawned via github.com/mudler/go-processmanager v0.1.1,
whose getSysProcAttr() sets Setpgid:true (own process group, so the group can be
signalled) but never PR_SET_PDEATHSIG/Pdeathsig, and exposes no Config field or
option for a caller to inject/extend SysProcAttr. LocalAI fully delegates
spawning to that library (it never builds the exec.Cmd itself), so it cannot set
a kernel parent-death signal at the spawn site. If LocalAI is SIGKILLed, nothing
tells the backend to exit and it is reparented to init.

Fix: add a best-effort, backend-side safety net at the one shared choke point
every out-of-process Go backend routes through — grpc.StartServer / RunServer in
pkg/grpc. On startup it captures getppid() and polls; when the process is
reparented (getppid changes / becomes 1 — the standard POSIX signal the original
parent died) it logs and self-terminates. getppid() reparent detection is
portable (Linux + macOS), unlike Linux-only PR_SET_PDEATHSIG. Toggle via
LOCALAI_BACKEND_PARENT_WATCH (default on; off on Windows) and
LOCALAI_BACKEND_PARENT_WATCH_INTERVAL. This is strictly a backstop alongside the
existing graceful SIGTERM->grace->SIGKILL teardown, which is unchanged.

Scope/limitations: covers Go-based backends (everything using pkg/grpc). The
C++ backends (e.g. llama-cpp) and Python backends do not route through
pkg/grpc and are not covered by this mechanism — they would each need an
equivalent parent-death check (follow-up). The fully general fix is for
go-processmanager to expose SysProcAttr injection so LocalAI can set Pdeathsig
at spawn for every backend regardless of language (suggested upstream follow-up;
out of scope for this LocalAI-only PR).

Test: pkg/grpc/parentwatch_test.go builds a real test -> middle -> grandchild
process tree, lets the middle process exit to orphan the grandchild running the
real watchParentDeath, and asserts it detects the reparent and self-terminates.
Unix-only (build-tagged), runs in CI (Linux).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* fix(process): extend parent-death backstop to C++ and Python backends

The Go parent-death watcher (pkg/grpc/parentwatch.go, commit 772b435d5)
only protects backends that route through pkg/grpc. C++ and Python
backends don't, so the originally-reported case — the llama.cpp gRPC
worker surviving a non-graceful LocalAI death — was still uncovered.

Extend the same best-effort backstop to both languages, reusing the
exact mechanism and semantics:

- capture getppid() at startup, skip if already orphaned (<=1)
- a background thread polls getppid() and self-exits on reparenting
  (getppid() != orig || == 1), portable across Linux/macOS, no-op on
  Windows
- same env vars: LOCALAI_BACKEND_PARENT_WATCH (default on; falsy
  false/0/no/off disable) and LOCALAI_BACKEND_PARENT_WATCH_INTERVAL
  (default 2s; accepts Go-style durations like 500ms/2s/1m)

C++: implemented in backend/cpp/llama-cpp (the reported, most-used C++
backend) as a dependency-free header parent_watch.h, wired into
grpc-server.cpp's main() and copied at build time via prepare.sh. C++
backends have no shared server scaffolding, so other C++ backends
(ds4, ik-llama-cpp, privacy-filter, ...) are not yet covered and would
each need the same one-line include+call as follow-ups.

Python: implemented once in the shared common/parent_watch.py and armed
from common/grpc_auth.py's get_auth_interceptors() — the single helper
every one of the 35 Python backends invokes while building its gRPC
server — so all Python backends (and future ones) are covered with no
per-backend edits and no duplicated implementation.

Tests (real process-tree reparent detection, mirroring the Go test):
- backend/cpp/llama-cpp/parent_watch_test.cpp (via run-unit-tests.sh)
- backend/python/common/parent_watch_test.py (python -m unittest)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

backend/python/common/parent_watch_test.py

@@ -0,0 +1,150 @@
+"""Unit tests for the parent-death watcher (parent_watch.py).
+
+Run standalone (Python standard library only, no backend venv needed):
+    python3 -m unittest parent_watch_test
+
+The core test (test_detects_reparent) builds a genuine two-level process tree
+(test -> middle -> grandchild) with os.fork, lets the middle process die, and
+asserts the grandchild's parent_watch._watch detects the reparenting and
+self-terminates — mirroring the Go test in pkg/grpc/parentwatch_test.go and the
+C++ test in backend/cpp/llama-cpp/parent_watch_test.cpp.
+"""
+
+import os
+import sys
+import tempfile
+import threading
+import time
+import unittest
+
+import parent_watch
+
+
+class TestParentWatchEnvParsing(unittest.TestCase):
+    def setUp(self):
+        self._saved = {
+            k: os.environ.get(k)
+            for k in (parent_watch.ENV_PARENT_WATCH, parent_watch.ENV_PARENT_WATCH_INTERVAL)
+        }
+        for k in self._saved:
+            os.environ.pop(k, None)
+
+    def tearDown(self):
+        for k, v in self._saved.items():
+            if v is None:
+                os.environ.pop(k, None)
+            else:
+                os.environ[k] = v
+
+    def test_interval_default(self):
+        self.assertEqual(parent_watch._interval_seconds(), 2.0)
+
+    def test_interval_units(self):
+        cases = {"500ms": 0.5, "2s": 2.0, "1m": 60.0, "3": 3.0, "0.5s": 0.5}
+        for raw, expected in cases.items():
+            os.environ[parent_watch.ENV_PARENT_WATCH_INTERVAL] = raw
+            self.assertAlmostEqual(parent_watch._interval_seconds(), expected, msg=raw)
+
+    def test_interval_garbage_falls_back(self):
+        os.environ[parent_watch.ENV_PARENT_WATCH_INTERVAL] = "garbage"
+        self.assertEqual(parent_watch._interval_seconds(), 2.0)
+
+    @unittest.skipIf(os.name == "nt" or sys.platform.startswith("win"), "POSIX only")
+    def test_enabled_default(self):
+        self.assertTrue(parent_watch._enabled())
+
+    @unittest.skipIf(os.name == "nt" or sys.platform.startswith("win"), "POSIX only")
+    def test_disabled_by_falsey(self):
+        for val in ("false", "0", "no", "off", "OFF", " False "):
+            os.environ[parent_watch.ENV_PARENT_WATCH] = val
+            self.assertFalse(parent_watch._enabled(), msg=val)
+
+    @unittest.skipIf(os.name == "nt" or sys.platform.startswith("win"), "POSIX only")
+    def test_enabled_by_truthy(self):
+        for val in ("true", "1", "yes", "on"):
+            os.environ[parent_watch.ENV_PARENT_WATCH] = val
+            self.assertTrue(parent_watch._enabled(), msg=val)
+
+
+@unittest.skipIf(os.name == "nt" or sys.platform.startswith("win"), "fork/reparent is POSIX only")
+class TestParentWatchReparent(unittest.TestCase):
+    def _wait_for_file(self, path, timeout=10.0):
+        deadline = time.time() + timeout
+        while time.time() < deadline:
+            if os.path.exists(path):
+                return True
+            time.sleep(0.02)
+        return False
+
+    def test_detects_reparent(self):
+        tmpdir = tempfile.mkdtemp(prefix="parentwatch_test_")
+        ready_file = os.path.join(tmpdir, "ready")
+        exited_file = os.path.join(tmpdir, "exited")
+
+        middle = os.fork()
+        if middle == 0:
+            # ---- middle process ----
+            grandchild = os.fork()
+            if grandchild == 0:
+                # ---- grandchild process: arm the REAL watcher against middle ----
+                orig_ppid = os.getppid()
+
+                def on_death():
+                    with open(exited_file, "w") as f:
+                        f.write("1")
+                    os._exit(7)
+
+                threading.Thread(
+                    target=parent_watch._watch,
+                    args=(orig_ppid, 0.05, on_death),
+                    daemon=True,
+                ).start()
+
+                # Safety valve: never linger if something goes wrong.
+                def bail():
+                    time.sleep(30)
+                    os._exit(2)
+
+                threading.Thread(target=bail, daemon=True).start()
+
+                # Signal readiness only after the watcher captured orig_ppid.
+                with open(ready_file, "w") as f:
+                    f.write(str(os.getpid()))
+                while True:
+                    time.sleep(1)
+            else:
+                # middle: wait until grandchild is ready, then exit to orphan it.
+                if not self._wait_for_file(ready_file):
+                    os._exit(5)
+                os._exit(0)
+
+        # ---- test (top) process ----
+        os.waitpid(middle, 0)  # reap middle only; grandchild is orphaned
+
+        self.assertTrue(os.path.exists(ready_file), "grandchild never signaled readiness")
+        self.assertTrue(
+            self._wait_for_file(exited_file),
+            "watcher did not detect parent death within timeout",
+        )
+
+        # Best-effort cleanup: kill the grandchild if it somehow survived.
+        try:
+            with open(ready_file) as f:
+                pid = int(f.read().strip())
+            if pid > 1:
+                os.kill(pid, 9)
+        except (OSError, ValueError):
+            pass
+        for p in (ready_file, exited_file):
+            try:
+                os.remove(p)
+            except OSError:
+                pass
+        try:
+            os.rmdir(tmpdir)
+        except OSError:
+            pass
+
+
+if __name__ == "__main__":
+    unittest.main()