Merge pull request #2116 from kacpherek/fix/2095-signal-save

🤖 Agent: Read against the vanilla 26.3 sources (Save the world on SIGTERM, Ctrl+C and SIGHUP) and proven in contrib-gate-21's union of 72 kacpherek PRs: 95 parity harnesses on playhorizon and the Mac mini, clippy, 1534 tests, lan_e2e 23 checks in-frame and with --server-thread. Thanks @kacpherek!

crates/horizon-client/src/game.rs

@@ -8772,6 +8772,10 @@ impl Game<'_> {
         }
         self.lan_close(false);
         self.save_game()?;
+        if let Some(mut remote) = self.remote.take() {
+            // Minecraft.disconnect closes the connection, so the host sees a clean leave.
+            remote.session.disconnect();
+        }
         self.saved_for_exit = true;
         Ok(())
     }
@@ -12773,6 +12777,16 @@ impl ApplicationHandler for Game<'_> {
         }
     }
     fn about_to_wait(&mut self, event_loop: &ActiveEventLoop) {
+        if horizon_threads::stop_requests() > 0
+            && self.pending_save.as_ref().is_none_or(|save| !save.quit)
+        {
+            // SIGTERM, SIGINT or SIGHUP: the shutdown hook's server halt, as a window close.
+            if let Err(error) = self.begin_closing_save(true) {
+                self.error = Some(error);
+                event_loop.exit();
+                return;
+            }
+        }
         if self.pending_save.is_some() {
             match self.poll_closing_save() {
                 Ok(true) => event_loop.exit(),
@@ -14263,6 +14277,11 @@ impl Loading {
         }
     }
     fn about_to_wait(&mut self, event_loop: &ActiveEventLoop) {
+        if horizon_threads::stop_requests() > 0 {
+            // No world is open yet: nothing to save.
+            event_loop.exit();
+            return;
+        }
         if let Err(error) = self.poll_menu_resources() {
             self.error = Some(error);
             event_loop.exit();
@@ -14540,6 +14559,9 @@ pub fn run() -> Result<()> {
     {
         horizon_client::heartbeat::start();
     }
+    if options.execution_role.is_client() {
+        horizon_threads::catch_stop_signals();
+    }
     let started = Instant::now();
     horizon_client::spans::enable(options.spikes.is_some());
     let vanilla_root = options.resources.clone();

crates/horizon-threads/src/lib.rs

@@ -163,6 +163,38 @@ fn idle() -> bool {
     false
 }
 
+/// How many stop requests (Ctrl-C, SIGTERM, SIGHUP) arrived since `catch_stop_signals`.
+pub fn stop_requests() -> u32 {
+    STOP_REQUESTS.load(std::sync::atomic::Ordering::SeqCst)
+}
+
+static STOP_REQUESTS: std::sync::atomic::AtomicU32 = std::sync::atomic::AtomicU32::new(0);
+
+/// Count stop requests from outside instead of dying on them: vanilla's "Client Shutdown Thread"
+/// (`Main.java`) halts the integrated server when the JVM shuts down, and the JVM does that on
+/// these signals, so a killed game still saves. The caller's event loop turns the first request
+/// into a normal quit; a second one (the save is stuck) ends the process at once.
+#[cfg(any(target_vendor = "apple", target_os = "linux", target_os = "android"))]
+pub fn catch_stop_signals() {
+    extern "C" fn handle(_: libc::c_int) {
+        if STOP_REQUESTS.fetch_add(1, Ordering::SeqCst) >= 1 {
+            // SAFETY: _exit is async-signal-safe; 130 is the shell's code for a Ctrl-C death.
+            unsafe { libc::_exit(130) }
+        }
+    }
+    let handler = handle as extern "C" fn(libc::c_int);
+    for signal in [libc::SIGINT, libc::SIGTERM, libc::SIGHUP] {
+        // SAFETY: the handler only touches an atomic and calls _exit, both async-signal-safe.
+        unsafe {
+            libc::signal(signal, handler as libc::sighandler_t);
+        }
+    }
+}
+
+/// Windows and the other systems keep their default: a closed window is a `CloseRequested`.
+#[cfg(not(any(target_vendor = "apple", target_os = "linux", target_os = "android")))]
+pub fn catch_stop_signals() {}
+
 /// Give back to the OS the memory the allocator holds free, after something
 /// large was dropped: glibc keeps freed pages in the arena of the thread that
 /// allocated them, and macOS in its zones until memory runs short. Nothing