poc: add heartbeat functionality to native backend

examples/example.c

@@ -20,6 +20,7 @@
 
 #ifdef SENTRY_PLATFORM_WINDOWS
 #    include <malloc.h>
+#    include <process.h>
 #    include <synchapi.h>
 #    define sleep_s(SECONDS) Sleep((SECONDS) * 1000)
 #else
@@ -533,6 +534,22 @@ run_threads(thread_func_t func)
 }
 #endif
 
+#if defined(SENTRY_PLATFORM_WINDOWS)
+static unsigned __stdcall
+app_hang_demo_thread(void *arg)
+{
+    (void)arg;
+    /* Heartbeat for 500 ms to latch this thread as the target. */
+    for (int i = 0; i < 10; i++) {
+        sentry_app_hang_heartbeat();
+        Sleep(50);
+    }
+    /* Freeze for 3x the configured timeout (3000 ms). */
+    Sleep(3000);
+    return 0;
+}
+#endif
+
 int
 main(int argc, char **argv)
 {
@@ -784,6 +801,13 @@ main(int argc, char **argv)
         }
     }
 
+#if defined(SENTRY_PLATFORM_WINDOWS)
+    if (has_arg(argc, argv, "app-hang")) {
+        sentry_options_set_app_hang_enabled(options, 1);
+        sentry_options_set_app_hang_timeout_ms(options, 1000);
+    }
+#endif
+
     // E2E test mode: generate unique test ID for event correlation
     char e2e_test_id[37] = { 0 };
     if (has_arg(argc, argv, "e2e-test")) {
@@ -795,6 +819,25 @@ main(int argc, char **argv)
         return EXIT_FAILURE;
     }
 
+#if defined(SENTRY_PLATFORM_WINDOWS)
+    /* app-hang: spawn the demo thread BEFORE any other post-init work so it
+     * begins heartbeating immediately. The thread freezes for 3x the timeout,
+     * giving the daemon time to detect the hang and ship the envelope. We wait
+     * for it here so main does not exit before the transport has flushed.
+     * NOTE: this mode is intentionally exclusive – do not combine with crash/
+     *       abort/etc. since those would terminate the process first. */
+    if (has_arg(argc, argv, "app-hang")) {
+        HANDLE t = (HANDLE)_beginthreadex(
+            NULL, 0, app_hang_demo_thread, NULL, 0, NULL);
+        if (t) {
+            WaitForSingleObject(t, INFINITE);
+            CloseHandle(t);
+        }
+        sentry_close();
+        return EXIT_SUCCESS;
+    }
+#endif
+
     if (has_arg(argc, argv, "user-consent-revoke")) {
         sentry_user_consent_revoke();
     }

include/sentry.h

@@ -1678,6 +1678,48 @@ SENTRY_EXPERIMENTAL_API void sentry_options_set_attach_session_replay(
 SENTRY_EXPERIMENTAL_API void sentry_options_set_session_replay_duration(
     sentry_options_t *opts, uint32_t duration_ms);
 
+/**
+ * Enable app-hang detection in the native crash backend.
+ *
+ * When enabled, the out-of-process daemon monitors a designated thread in the
+ * host via a shared-memory heartbeat. If the heartbeat goes stale for longer
+ * than the configured timeout, the daemon walks the thread's stack remotely and
+ * emits an `ApplicationNotResponding` event. The host process keeps running.
+ *
+ * Off by default. This setting only has an effect when using the `native`
+ * backend. In this initial release the feature is Windows-only; the call is a
+ * silent no-op on other platforms.
+ */
+SENTRY_EXPERIMENTAL_API void sentry_options_set_app_hang_enabled(
+    sentry_options_t *opts, int enabled);
+
+/**
+ * Sets the heartbeat-staleness threshold (in milliseconds) used by the
+ * app-hang detector. Default 5000 ms.
+ *
+ * Read by the daemon once at startup; changes after `sentry_init` have no
+ * effect.
+ */
+SENTRY_EXPERIMENTAL_API void sentry_options_set_app_hang_timeout_ms(
+    sentry_options_t *opts, uint64_t timeout_ms);
+
+/**
+ * Signal that the calling thread is alive.
+ *
+ * Call this from the thread you want monitored (typically the main / game
+ * thread). The first call latches the calling thread's id as the target;
+ * subsequent calls from the same thread refresh the heartbeat timestamp. Calls
+ * from any other thread are dropped — so a stray heartbeat from a worker
+ * thread cannot mask a frozen main thread.
+ *
+ * Cost: approximately one system call plus a relaxed 64-bit store. Safe to
+ * call from a per-frame hook in a game engine.
+ *
+ * No-op if app-hang detection is not enabled in options, or if the native
+ * backend is not active, or on non-Windows platforms.
+ */
+SENTRY_EXPERIMENTAL_API void sentry_app_hang_heartbeat(void);
+
 /**
  * Sets the path to the crashpad handler if the crashpad backend is used.
  *

src/CMakeLists.txt

@@ -1,6 +1,8 @@
 sentry_target_sources_cwd(sentry
 	sentry_alloc.c
 	sentry_alloc.h
+	sentry_app_hang.c
+	sentry_app_hang.h
 	sentry_attachment.c
 	sentry_attachment.h
 	sentry_backend.c

src/backends/native/sentry_crash_context.h

@@ -321,6 +321,22 @@ typedef struct {
     uint32_t module_count;
     sentry_module_info_t modules[SENTRY_CRASH_MAX_MODULES];
 
+    /* App-hang detection (Windows-only, native backend only).
+     *
+     * Sync model:
+     *  - app_hang_enabled, app_hang_timeout_ms: written by host before daemon
+     *    is signalled ready; read by daemon at startup. No further mutation.
+     *  - app_hang_target_tid: latched once by host on first heartbeat (release
+     *    store via InterlockedCompareExchange64). Daemon reads, never writes.
+     *  - app_hang_last_heartbeat_ms: written on every heartbeat with a relaxed
+     *    64-bit store. Daemon reads with a relaxed load. Torn reads are not a
+     *    correctness issue — the daemon compares against its remembered value
+     *    from the previous tick. */
+    bool app_hang_enabled;
+    uint64_t app_hang_timeout_ms;
+    volatile uint64_t app_hang_target_tid;
+    volatile uint64_t app_hang_last_heartbeat_ms;
+
 } sentry_crash_context_t;
 
 // Shared memory size: calculated at compile-time based on actual struct size