455 lines
19 KiB
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455 lines
19 KiB
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<ol class="chapter"><li class="affix"><a href="introduction.html">Introduction</a></li><li><a href="1_why_futures.html"><strong aria-hidden="true">1.</strong> Why Futures</a></li><li><a href="1_background_information.html"><strong aria-hidden="true">2.</strong> Some background information</a></li><li><a href="2_waker_context.html"><strong aria-hidden="true">3.</strong> Waker and Context</a></li><li><a href="3_generators_pin.html"><strong aria-hidden="true">4.</strong> Generators</a></li><li><a href="4_pin.html"><strong aria-hidden="true">5.</strong> Pin</a></li><li><a href="6_future_example.html"><strong aria-hidden="true">6.</strong> Futures - our main example</a></li><li><a href="8_finished_example.html" class="active"><strong aria-hidden="true">7.</strong> Finished example (editable)</a></li><li class="affix"><a href="conclusion.html">Conclusion and exercises</a></li></ol>
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<h1 class="menu-title">Futures Explained in 200 Lines of Rust</h1>
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<main>
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<h1><a class="header" href="#our-finished-code" id="our-finished-code">Our finished code</a></h1>
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<p>Here is the whole example. You can edit it right here in your browser and
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run it yourself. Have fun!</p>
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<pre><pre class="playpen"><code class="language-rust editable edition2018">use std::{
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future::Future, pin::Pin, sync::{mpsc::{channel, Sender}, Arc, Mutex},
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task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
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thread::{self, JoinHandle}, time::{Duration, Instant}
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};
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fn main() {
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let start = Instant::now();
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let reactor = Reactor::new();
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let reactor = Arc::new(Mutex::new(reactor));
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let future1 = Task::new(reactor.clone(), 1, 1);
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let future2 = Task::new(reactor.clone(), 2, 2);
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let fut1 = async {
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let val = future1.await;
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let dur = (Instant::now() - start).as_secs_f32();
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println!("Future got {} at time: {:.2}.", val, dur);
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};
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let fut2 = async {
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let val = future2.await;
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let dur = (Instant::now() - start).as_secs_f32();
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println!("Future got {} at time: {:.2}.", val, dur);
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};
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let mainfut = async {
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let handle1 = spawn(fut1);
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let handle2 = spawn(fut2);
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handle1.await;
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handle2.await;
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};
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block_on(mainfut);
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reactor.lock().map(|mut r| r.close()).unwrap();
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}
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// ============================= EXECUTOR ====================================
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fn block_on<F: Future>(mut future: F) -> F::Output {
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let mywaker = Arc::new(MyWaker{ thread: thread::current() });
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let waker = waker_into_waker(Arc::into_raw(mywaker));
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let mut cx = Context::from_waker(&waker);
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let val = loop {
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let pinned = unsafe { Pin::new_unchecked(&mut future) };
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match Future::poll(pinned, &mut cx) {
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Poll::Ready(val) => break val,
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Poll::Pending => thread::park(),
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};
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};
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val
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}
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fn spawn<F: Future>(future: F) -> Pin<Box<F>> {
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let mywaker = Arc::new(MyWaker{ thread: thread::current() });
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let waker = waker_into_waker(Arc::into_raw(mywaker));
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let mut cx = Context::from_waker(&waker);
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let mut boxed = Box::pin(future);
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let _ = Future::poll(boxed.as_mut(), &mut cx);
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boxed
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}
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// ====================== FUTURE IMPLEMENTATION ==============================
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#[derive(Clone)]
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struct MyWaker {
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thread: thread::Thread,
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}
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#[derive(Clone)]
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pub struct Task {
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id: usize,
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reactor: Arc<Mutex<Reactor>>,
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data: u64,
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is_registered: bool,
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}
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fn mywaker_wake(s: &MyWaker) {
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let waker_ptr: *const MyWaker = s;
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let waker_arc = unsafe {Arc::from_raw(waker_ptr)};
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waker_arc.thread.unpark();
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}
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fn mywaker_clone(s: &MyWaker) -> RawWaker {
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let arc = unsafe { Arc::from_raw(s).clone() };
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std::mem::forget(arc.clone()); // increase ref count
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RawWaker::new(Arc::into_raw(arc) as *const (), &VTABLE)
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}
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const VTABLE: RawWakerVTable = unsafe {
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RawWakerVTable::new(
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|s| mywaker_clone(&*(s as *const MyWaker)), // clone
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|s| mywaker_wake(&*(s as *const MyWaker)), // wake
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|s| mywaker_wake(*(s as *const &MyWaker)), // wake by ref
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|s| drop(Arc::from_raw(s as *const MyWaker)), // decrease refcount
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)
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};
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fn waker_into_waker(s: *const MyWaker) -> Waker {
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let raw_waker = RawWaker::new(s as *const (), &VTABLE);
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unsafe { Waker::from_raw(raw_waker) }
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}
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impl Task {
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fn new(reactor: Arc<Mutex<Reactor>>, data: u64, id: usize) -> Self {
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Task {
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id,
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reactor,
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data,
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is_registered: false,
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}
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}
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}
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impl Future for Task {
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type Output = usize;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let mut r = self.reactor.lock().unwrap();
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if r.is_ready(self.id) {
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Poll::Ready(self.id)
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} else if self.is_registered {
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Poll::Pending
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} else {
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r.register(self.data, cx.waker().clone(), self.id);
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drop(r);
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self.is_registered = true;
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Poll::Pending
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}
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}
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}
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// =============================== REACTOR ===================================
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struct Reactor {
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dispatcher: Sender<Event>,
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handle: Option<JoinHandle<()>>,
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readylist: Arc<Mutex<Vec<usize>>>,
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}
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#[derive(Debug)]
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enum Event {
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Close,
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Timeout(Waker, u64, usize),
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}
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impl Reactor {
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fn new() -> Self {
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let (tx, rx) = channel::<Event>();
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let readylist = Arc::new(Mutex::new(vec![]));
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let rl_clone = readylist.clone();
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let mut handles = vec![];
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let handle = thread::spawn(move || {
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// This simulates some I/O resource
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for event in rx {
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println!("REACTOR: {:?}", event);
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let rl_clone = rl_clone.clone();
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match event {
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Event::Close => break,
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Event::Timeout(waker, duration, id) => {
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let event_handle = thread::spawn(move || {
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thread::sleep(Duration::from_secs(duration));
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rl_clone.lock().map(|mut rl| rl.push(id)).unwrap();
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waker.wake();
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});
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handles.push(event_handle);
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}
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}
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}
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for handle in handles {
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handle.join().unwrap();
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}
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});
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Reactor {
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readylist,
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dispatcher: tx,
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handle: Some(handle),
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}
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}
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fn register(&mut self, duration: u64, waker: Waker, data: usize) {
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self.dispatcher
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.send(Event::Timeout(waker, duration, data))
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.unwrap();
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}
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fn close(&mut self) {
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self.dispatcher.send(Event::Close).unwrap();
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}
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fn is_ready(&self, id_to_check: usize) -> bool {
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self.readylist
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.lock()
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.map(|rl| rl.iter().any(|id| *id == id_to_check))
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.unwrap()
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}
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}
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impl Drop for Reactor {
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fn drop(&mut self) {
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self.handle.take().map(|h| h.join().unwrap()).unwrap();
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}
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}
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</code></pre></pre>
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