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//! The event loop of an [`App`]: [`App::run`] (poll crossterm, route,
//! tick, draw), the poll timeout that wakes it for the next timer, caret
//! blink, smooth-scroll step or autoscroll tick, the scheduler pump, the
//! virtual clock of [`App::advance`], the `on_tick` callback and the
//! [`AppHandle`](super::AppHandle) drains.
use std::io::{self, Stdout};
use std::panic::{self, AssertUnwindSafe};
use std::sync::atomic::Ordering;
use std::time::Duration;
use crossterm::event;
use super::autoscroll::AUTOSCROLL_PERIOD;
use super::redraw::Redraw;
use super::{App, AppContext, ControlFlow};
use crate::render::backend::Backend;
use crate::render::backend_crossterm::{CrosstermBackend, leave_tui_mode};
impl App<CrosstermBackend<Stdout>> {
/// Block until exit. Runs the event loop: poll crossterm, route
/// events, tick, cascade + layout + paint when dirty. Exits on
/// `ControlFlow::Quit`, Ctrl-C, or `AppContext::quit()`.
///
/// On exit, the terminal is restored via [`leave_tui_mode`].
/// This is also guaranteed on panic — the `Drop` impl on `App`
/// runs it if `run` unwinds.
pub fn run(mut self) -> io::Result<()> {
// Initial paint — user should see something even before any
// event fires.
self.redraw.note(Redraw::Cascade);
// Wrap the whole loop in catch_unwind. If a listener panics
// mid-handler, the terminal state is still restored via the
// `TerminalGuard` held in `self.guard` (dropped on unwind),
// then we resume_unwind to propagate the panic to the
// caller with a usable shell behind it.
//
// AssertUnwindSafe: `App` holds Rc-based state (Tree,
// DirtyTracker observers) that Rust's unwind-safety
// analysis flags as !UnwindSafe. In practice the loop body
// either completes the iteration or panics; there's no
// "partial" state the caller can inspect after a panic
// (we re-panic). Explicit assertion is appropriate.
let loop_result = panic::catch_unwind(AssertUnwindSafe(|| -> io::Result<()> {
self.draw_if_dirty()?;
loop {
self.drain_handle_signals();
if self.should_quit {
break;
}
let poll_timeout = self.compute_poll_timeout();
let has_event = event::poll(poll_timeout).unwrap_or(false);
if has_event {
// Drain ALL currently-queued events before
// drawing. At ~100Hz mouse motion, processing
// one event then drawing then processing the
// next means each paint (which can be 80ms+
// for a complex scene) lets ~8 motion events
// queue up. The hover state visibly lags
// behind the cursor. Draining collapses a
// burst into a single paint that reflects the
// final state — same pattern ratatui apps
// use. We still bound the drain to whatever's
// queued right now: an infinite tight drain
// would starve drawing if events arrive
// faster than we can drain.
loop {
match event::read() {
Ok(ev) => {
crate::rdom_trace!("event::read() -> Ok({ev:?})");
// Multi-click / type-ahead windows read the
// scheduler clock; sync it per event so a
// drained burst does not share one stale
// instant (`advance` never comes through
// here, so it stays deterministic).
self.scheduler
.borrow_mut()
.set_now(std::time::Instant::now());
self.handle_event(ev);
}
Err(e) => {
crate::rdom_trace!("event::read() -> Err({e:?})");
break;
}
}
// Zero-timeout poll: only continue if
// another event is already buffered. As
// soon as the queue drains we exit the
// loop and proceed to draw.
if !event::poll(std::time::Duration::ZERO).unwrap_or(false) {
break;
}
}
} else {
self.tick();
}
// M3: advance the scheduler clock and pump expired
// work. Microtasks drain after every chunk so that
// chained queue_microtask calls during a callback
// run before the next paint, matching HTML spec.
self.pump_scheduler();
self.service_autoscroll();
self.drain_handle_injections();
self.draw_if_dirty()?;
}
Ok(())
}));
// Whether we exited normally or via panic, restore the
// terminal now. The TerminalGuard drop would also do this,
// but explicitly doing it here keeps the ordering clear
// (restore → propagate the Result / panic).
let mut stdout = io::stdout();
let _ = leave_tui_mode(&mut stdout);
match loop_result {
Ok(inner_result) => inner_result,
Err(payload) => panic::resume_unwind(payload),
}
}
}
impl<B: Backend> App<B> {
/// Compute the right `poll` timeout based on the next
/// scheduled deadline + tick rate + animation frame budget.
/// When the scheduler has nothing pending, this is just
/// `tick_rate` — preserves the original idle behavior.
fn compute_poll_timeout(&self) -> Duration {
let now = std::time::Instant::now();
let to_deadline = self
.scheduler
.borrow()
.next_deadline()
.map(|d| d.saturating_duration_since(now))
.unwrap_or(self.tick_rate);
// If we have pending rAF callbacks (= an animation
// frame is queued), tighten to the frame budget.
let frame_floor = if self.scheduler.borrow().has_active_raf() {
Duration::from_millis(self.animation_frame_ms as u64)
} else {
self.tick_rate
};
let mut base = to_deadline.min(frame_floor).min(self.tick_rate);
if let Some(flip) = self.prelude.caret_blink.next_deadline() {
base = base.min(flip.saturating_duration_since(now));
}
if let Some(step) = self.prelude.smooth_scroll_next {
base = base.min(step.saturating_duration_since(now));
}
// While a drag-autoscroll is armed, wake at least once per period so the
// tick fires even with the pointer held still (no new input events).
if self.autoscroll.pointer.is_some() {
base.min(AUTOSCROLL_PERIOD)
} else {
base
}
}
/// Pump the scheduler: advance the clock, drain microtasks,
/// fire expired timeouts/intervals, drain microtasks again
/// (callbacks may queue them), then drain rAF before paint.
fn pump_scheduler(&mut self) {
// Sync the clock to wall time — production only ever
// moves forward; tests use the virtual-clock API
// (`advance`) directly.
self.scheduler
.borrow_mut()
.set_now(std::time::Instant::now());
self.pump_due();
}
/// Drain everything due at the scheduler's *current* clock — microtasks,
/// expired timeouts/intervals, then rAF — without touching the clock.
/// `pump_scheduler` (live loop) syncs the clock to wall time first;
/// `advance` (headless/test) moves the virtual clock first. Both then call
/// this so the drain order is identical.
fn pump_due(&mut self) {
use crate::runtime::timers as t;
// Microtasks first, in case a previous handler queued
// one and we haven't drained yet.
let sched = self.scheduler.clone();
// One checkpoint for anything queued since the last task; each
// pump then checkpoints after every callback it runs (HTML
// §8.1.7.3), so nothing is left for a trailing drain.
// The callbacks count as having touched the App only when they
// left evidence of a change (`P7G-TICK-TOUCHED-1`): an interval
// that fires and changes nothing leaves the next frame's
// whole-tree checks skipped.
let before = self.change_evidence();
t::drain_microtasks(&sched, &mut self.dom);
t::pump_timeouts(&sched, &mut self.dom);
let due = sched.borrow().drain_expired_interval_ids();
t::pump_intervals(&sched, &mut self.dom, &due);
t::pump_raf(&sched, &mut self.dom);
self.prelude.touched |= self.change_evidence() != before;
}
/// Evidence that code the App ran changed what the frame's
/// whole-tree checks read (`P7G-TICK-TOUCHED-1`): the mutation
/// records the dirty tracker observed, and the runtime-managed
/// `TuiExt` writes no mutation reports (`runtime::state_writes`:
/// scroll offsets through the scroll API, smooth scrolls, custom
/// validity). Compared before and after a callback.
fn change_evidence(&self) -> (u64, u64) {
(
self.tracker.records_seen(),
crate::runtime::state_writes::generation(),
)
}
/// Advance the virtual scheduler clock by `ms` and service everything that
/// comes due, then redraw if dirty. For **headless / simulation / test**
/// drivers that don't run the live [`run`](Self::run) loop (which syncs to
/// wall time). Fires timeouts, intervals, rAF, and microtasks whose deadline
/// falls within the elapsed window, services drag autoscroll, and runs the
/// closures queued by [`AppHandle::inject`](super::AppHandle::inject), exactly as the loop would —
/// making timer-driven runtime behavior (animations, autoscroll) and
/// handler-queued work (stylesheet intents) deterministically testable.
/// `advance(0)` finishes the current loop iteration without moving the
/// clock. Advance one period at a time to step a repeating timer
/// tick-by-tick.
pub fn advance(&mut self, ms: u64) -> io::Result<()> {
let _current = crate::runtime::timers::SchedulerGuard::install(&self.scheduler);
let target = self.scheduler.borrow().now() + std::time::Duration::from_millis(ms);
self.scheduler.borrow_mut().set_now(target);
self.pump_due();
self.service_autoscroll();
self.drain_handle_injections();
self.draw_if_dirty()
}
/// Fire the registered `on_tick` callback, if any. No-op when
/// unset.
pub(crate) fn tick(&mut self) {
let Some(mut cb) = self.on_tick.take() else {
return;
};
// Touched only on evidence of a change: the documented pattern of
// draining an (often empty) channel here must not walk the tree
// every tick (`P7G-TICK-TOUCHED-1`).
let before = self.change_evidence();
// Install the scheduler thread-local so on_tick handlers
// can use the `TuiTimers` extension surface too (apps
// that schedule fade-outs from a tick callback, etc.).
let _scheduler_guard = crate::runtime::timers::SchedulerGuard::install(&self.scheduler);
let (queued, intents) = {
let mut ctx = AppContext::new(&mut self.dom, &mut self.stylesheet_ids);
let flow = cb(&mut ctx);
self.redraw.note_if(ctx.redraw_requested, Redraw::Cascade);
// A `request_redraw` may follow a direct `TuiExt` write.
self.prelude.touched |= ctx.redraw_requested;
self.should_quit |= ctx.quit_requested || flow == ControlFlow::Quit;
(
std::mem::take(&mut ctx.queued_dispatches),
std::mem::take(&mut ctx.stylesheet_intents),
)
};
self.apply_stylesheet_intents(intents);
self.on_tick = Some(cb);
// Fire queued dispatches now — after the tick returns but
// before the next event poll, matching the HTML microtask
// queue. Each dispatch may itself mutate the DOM, triggering
// DirtyTracker updates.
super::context::run_queued_dispatches(&mut self.dom, queued);
self.prelude.touched |= self.change_evidence() != before;
}
/// Pull flags from the shared state into the local ones. Called
/// at the top of every loop iteration.
pub(crate) fn drain_handle_signals(&mut self) {
if self.shared.redraw_requested.swap(false, Ordering::Relaxed) {
self.redraw.note(Redraw::Cascade);
}
if self.shared.quit_requested.load(Ordering::Relaxed) {
self.should_quit = true;
}
}
/// Run any injected closures queued by an `AppHandle::inject`.
pub(crate) fn drain_handle_injections(&mut self) {
let injections = self.shared.drain_injections();
if injections.is_empty() {
return;
}
// As for `on_tick`: touched on evidence of a change only.
let before = self.change_evidence();
let _current = crate::runtime::timers::SchedulerGuard::install(&self.scheduler);
let mut queued = Vec::new();
for f in injections {
let mut ctx = AppContext::new(&mut self.dom, &mut self.stylesheet_ids);
f(&mut ctx);
self.redraw.note_if(ctx.redraw_requested, Redraw::Cascade);
self.prelude.touched |= ctx.redraw_requested;
self.should_quit |= ctx.quit_requested;
queued.extend(std::mem::take(&mut ctx.queued_dispatches));
let intents = std::mem::take(&mut ctx.stylesheet_intents);
self.apply_stylesheet_intents(intents);
}
super::context::run_queued_dispatches(&mut self.dom, queued);
self.prelude.touched |= self.change_evidence() != before;
}
}