perf: move session autosaves off main loop

1 files changed, 75 insertions, 0 deletions

diff --git a/src/app/mod.rs b/src/app/mod.rs
index 8f33e23a..51bdd33e 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -128,6 +128,7 @@ pub struct App {
     pub(crate) selection_autoscroll_deadline: Option<Instant>,
     pub(crate) selection_highlight_clear_deadline: Option<Instant>,
     pub(crate) session_save_deadline: Option<Instant>,
+    pub(crate) session_save_thread: Option<std::thread::JoinHandle<()>>,
     pub(crate) persist_pane_history: bool,
     pub(crate) last_render_at: Option<Instant>,
     pub(crate) suppressed_repeat_keys:
@@ -719,6 +720,7 @@ impl App {
             agent_metadata_deadline: None,
             pending_agent_resume_deadline: None,
             session_save_deadline: None,
+            session_save_thread: None,
             selection_autoscroll_deadline: None,
             selection_highlight_clear_deadline: None,
             persist_pane_history: config.experimental.pane_history,
@@ -1739,6 +1741,14 @@ mod tests {
         )
     }
 
+    fn unique_temp_path(name: &str) -> std::path::PathBuf {
+        let stamp = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap()
+            .as_nanos();
+        std::env::temp_dir().join(format!("herdr-{name}-{}-{stamp}", std::process::id()))
+    }
+
     #[cfg(windows)]
     fn exiting_test_command() -> &'static str {
         "C:\\Windows\\System32\\whoami.exe"
@@ -4076,6 +4086,71 @@ mod tests {
     }
 
     #[test]
+    fn due_session_save_starts_background_writer() {
+        let _guard = crate::config::test_config_env_lock().lock().unwrap();
+        let config_home = unique_temp_path("background-session-save");
+        std::env::set_var("XDG_CONFIG_HOME", &config_home);
+        std::env::remove_var(crate::session::SESSION_ENV_VAR);
+
+        let mut app = test_app();
+        app.no_session = false;
+        app.state.workspaces = vec![Workspace::test_new("autosave")];
+        app.state.ensure_test_terminals();
+        app.session_save_deadline = Some(Instant::now() - Duration::from_secs(1));
+
+        app.handle_scheduled_tasks(Instant::now(), false);
+
+        assert!(app.session_save_thread.is_some());
+        assert!(app.session_save_deadline.is_none());
+        app.save_session_now();
+        assert!(crate::session::data_dir().join("session.json").exists());
+
+        std::env::remove_var("XDG_CONFIG_HOME");
+        let _ = std::fs::remove_dir_all(config_home);
+    }
+
+    #[test]
+    fn background_session_save_reschedules_when_writer_is_busy() {
+        let mut app = test_app();
+        app.no_session = false;
+        let (release_tx, release_rx) = std::sync::mpsc::channel();
+        app.session_save_thread = Some(std::thread::spawn(move || {
+            let _ = release_rx.recv();
+        }));
+
+        app.start_background_session_save();
+
+        assert!(app.session_save_thread.is_some());
+        assert!(app.session_save_deadline.is_some());
+
+        release_tx.send(()).unwrap();
+        app.no_session = true;
+        app.save_session_now();
+    }
+
+    #[test]
+    fn final_session_save_joins_background_writer_before_returning() {
+        let mut app = test_app();
+        app.no_session = true;
+        let (release_tx, release_rx) = std::sync::mpsc::channel();
+        let (done_tx, done_rx) = std::sync::mpsc::channel();
+        app.session_save_thread = Some(std::thread::spawn(move || {
+            let _ = release_rx.recv();
+            done_tx.send(()).unwrap();
+        }));
+        let releaser = std::thread::spawn(move || {
+            std::thread::sleep(Duration::from_millis(30));
+            release_tx.send(()).unwrap();
+        });
+
+        app.save_session_now();
+
+        releaser.join().unwrap();
+        done_rx.try_recv().unwrap();
+        assert!(app.session_save_thread.is_none());
+    }
+
+    #[test]
     fn next_loop_deadline_includes_selection_autoscroll_deadline() {
         let mut app = test_app();
         let now = Instant::now();