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/cpp/llama-cpp/parent_watch.h

@@ -0,0 +1,179 @@
+// Parent-death watcher (best-effort backstop) for the llama.cpp gRPC backend.
+//
+// LocalAI spawns this backend as a child process and, on a clean shutdown,
+// tears it down itself (SIGTERM -> grace -> SIGKILL). That graceful path only
+// runs when LocalAI receives a catchable signal and lives long enough to run
+// its handlers. If LocalAI is SIGKILLed (e.g. a supervising process's grace
+// period elapses first), that teardown never runs and this backend would be
+// reparented to init and linger, holding VRAM and its listen port.
+//
+// The watcher here is a best-effort backstop for exactly that case: it does
+// NOT replace the graceful teardown, it only covers the "parent vanished
+// without cleaning up" path. It detects reparenting: when the process that
+// spawned this backend dies, the kernel reparents us to the nearest sub-reaper
+// or to init (PID 1), so getppid() stops matching the value captured at
+// startup. This getppid() approach is portable across Linux/macOS (unlike the
+// Linux-only PR_SET_PDEATHSIG), which is why it is used here, mirroring the Go
+// backends' pkg/grpc/parentwatch.go. It is disabled on Windows, which has no
+// equivalent orphan-reparenting semantics.
+//
+// This header is intentionally dependency-free (C++ standard library only) so
+// it can be exercised by a standalone unit test (parent_watch_test.cpp) without
+// building the full llama.cpp + gRPC backend.
+#ifndef LLAMA_GRPC_PARENT_WATCH_H
+#define LLAMA_GRPC_PARENT_WATCH_H
+
+#include <algorithm>
+#include <cctype>
+#include <chrono>
+#include <cstdio>
+#include <cstdlib>
+#include <functional>
+#include <string>
+#include <thread>
+
+#if !defined(_WIN32)
+#include <unistd.h> // getppid(2), _exit(2)
+#endif
+
+namespace llama_grpc {
+
+// Env var names are shared verbatim with the Go and Python backends for
+// consistency across languages.
+inline const char *kEnvParentWatch()         { return "LOCALAI_BACKEND_PARENT_WATCH"; }
+inline const char *kEnvParentWatchInterval() { return "LOCALAI_BACKEND_PARENT_WATCH_INTERVAL"; }
+
+// Default poll interval in milliseconds. Matches the Go side's 2 * time.Second.
+inline long parent_watch_default_interval_ms() { return 2000; }
+
+namespace detail {
+inline std::string trim_lower(const std::string &in, bool lower) {
+    size_t a = in.find_first_not_of(" \t\r\n");
+    size_t b = in.find_last_not_of(" \t\r\n");
+    if (a == std::string::npos) {
+        return "";
+    }
+    std::string s = in.substr(a, b - a + 1);
+    if (lower) {
+        std::transform(s.begin(), s.end(), s.begin(),
+                       [](unsigned char c) { return std::tolower(c); });
+    }
+    return s;
+}
+} // namespace detail
+
+// parent_watch_enabled reports whether the watcher should run. Enabled by
+// default; a falsey value ("false"/"0"/"no"/"off", case-insensitive) disables
+// it, matching the Go implementation's exact semantics.
+inline bool parent_watch_enabled() {
+#if defined(_WIN32)
+    return false;
+#else
+    const char *v = std::getenv(kEnvParentWatch());
+    if (v == nullptr || v[0] == '\0') {
+        return true;
+    }
+    const std::string s = detail::trim_lower(v, true);
+    return !(s == "false" || s == "0" || s == "no" || s == "off");
+#endif
+}
+
+// parent_watch_interval_ms returns the poll interval in milliseconds. Accepts
+// Go-style duration strings ("500ms", "2s", "1m") for cross-language parity, or
+// a bare number interpreted as seconds. Defaults to
+// parent_watch_default_interval_ms().
+inline long parent_watch_interval_ms() {
+    const long def = parent_watch_default_interval_ms();
+    const char *v = std::getenv(kEnvParentWatchInterval());
+    if (v == nullptr || v[0] == '\0') {
+        return def;
+    }
+    const std::string s = detail::trim_lower(v, false);
+    if (s.empty()) {
+        return def;
+    }
+    size_t i = 0;
+    while (i < s.size() && (std::isdigit((unsigned char)s[i]) || s[i] == '.')) {
+        i++;
+    }
+    if (i == 0) {
+        return def;
+    }
+    double num = 0.0;
+    try {
+        num = std::stod(s.substr(0, i));
+    } catch (...) {
+        return def;
+    }
+    const std::string unit = s.substr(i);
+    long ms;
+    if (unit == "ms") {
+        ms = (long)num;
+    } else if (unit == "s" || unit.empty()) {
+        ms = (long)(num * 1000.0);
+    } else if (unit == "m") {
+        ms = (long)(num * 60000.0);
+    } else {
+        return def; // unrecognized unit
+    }
+    return ms > 0 ? ms : def;
+}
+
+#if !defined(_WIN32)
+// parent_died reports whether this process has been reparented away from the
+// parent it had when the watcher started. Reparenting is the standard POSIX
+// signal that the original parent (here, the LocalAI process that spawned this
+// backend) has exited: the orphan is handed to the nearest sub-reaper or to
+// init (PID 1), so getppid() no longer matches the value captured at startup.
+inline bool parent_died(pid_t orig_ppid) {
+    const pid_t ppid = getppid();
+    return ppid != orig_ppid || ppid == 1;
+}
+
+// watch_parent_death polls until parent_died reports the original parent is
+// gone, then invokes on_death. It blocks, so run it on its own thread.
+inline void watch_parent_death(pid_t orig_ppid, long interval_ms,
+                               const std::function<void()> &on_death) {
+    for (;;) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(interval_ms));
+        if (parent_died(orig_ppid)) {
+            on_death();
+            return;
+        }
+    }
+}
+#endif
+
+// start_parent_death_watcher installs the best-effort safety net described in
+// the file header on the calling backend process. It is a no-op when disabled,
+// on Windows, or when the process is already orphaned at startup
+// (getppid() <= 1). This is a backstop alongside — never a replacement for —
+// LocalAI's graceful teardown.
+inline void start_parent_death_watcher() {
+#if !defined(_WIN32)
+    if (!parent_watch_enabled()) {
+        return;
+    }
+    const pid_t orig_ppid = getppid();
+    // A parent of 1 (or less) at startup means we were already orphaned (or
+    // launched directly under init) — there is no original parent to watch for.
+    if (orig_ppid <= 1) {
+        return;
+    }
+    const long interval_ms = parent_watch_interval_ms();
+    std::thread([orig_ppid, interval_ms]() {
+        watch_parent_death(orig_ppid, interval_ms, [orig_ppid]() {
+            fprintf(stderr,
+                    "backend parent process (pid %d) exited without stopping "
+                    "this backend; self-terminating to avoid orphaning\n",
+                    (int)orig_ppid);
+            fflush(stderr);
+            _exit(1);
+        });
+    }).detach();
+#endif
+}
+
+} // namespace llama_grpc
+
+#endif // LLAMA_GRPC_PARENT_WATCH_H