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use std::future::{join, Future};
use std::pin::Pin;
use std::sync::Arc;
use std::task::{Context, Poll, Wake};
use std::thread;
struct PollN {
val: usize,
polled: usize,
num: usize,
}
impl Future for PollN {
type Output = usize;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
self.polled += 1;
if self.polled == self.num {
return Poll::Ready(self.val);
}
cx.waker().wake_by_ref();
Poll::Pending
}
}
fn poll_n(val: usize, num: usize) -> PollN {
PollN { val, num, polled: 0 }
}
#[test]
#[cfg_attr(miri, ignore)] // self-referential generators do not work with Miri's aliasing checks
fn test_join() {
block_on(async move {
let x = join!(async { 0 }).await;
assert_eq!(x, 0);
let x = join!(async { 0 }, async { 1 }).await;
assert_eq!(x, (0, 1));
let x = join!(async { 0 }, async { 1 }, async { 2 }).await;
assert_eq!(x, (0, 1, 2));
let x = join!(
poll_n(0, 1),
poll_n(1, 5),
poll_n(2, 2),
poll_n(3, 1),
poll_n(4, 2),
poll_n(5, 3),
poll_n(6, 4),
poll_n(7, 1)
)
.await;
assert_eq!(x, (0, 1, 2, 3, 4, 5, 6, 7));
let y = String::new();
let x = join!(async {
println!("{}", &y);
1
})
.await;
assert_eq!(x, 1);
});
}
/// Tests that `join!(…)` behaves "like a function": evaluating its arguments
/// before applying any of its own logic.
///
/// _e.g._, `join!(async_fn(&borrowed), …)` does not consume `borrowed`;
/// and `join!(opt_fut?, …)` does let that `?` refer to the callsite scope.
mod test_join_function_like_value_arg_semantics {
use super::*;
async fn async_fn(_: impl Sized) {}
// no need to _run_ this test, just to compile it.
fn _join_does_not_unnecessarily_move_mentioned_bindings() {
let not_copy = vec![()];
let _ = join!(async_fn(¬_copy)); // should not move `not_copy`
let _ = ¬_copy; // OK
}
#[test]
fn join_lets_control_flow_effects_such_as_try_flow_through() {
let maybe_fut = None;
if false {
*&mut { maybe_fut } = Some(async {});
loop {}
}
assert!(Option::is_none(&try { join!(maybe_fut?, async { unreachable!() }) }));
}
#[test]
fn join_is_able_to_handle_temporaries() {
let _ = join!(async_fn(&String::from("temporary")));
let () = block_on(join!(async_fn(&String::from("temporary"))));
}
}
fn block_on(fut: impl Future) {
struct Waker;
impl Wake for Waker {
fn wake(self: Arc<Self>) {
thread::current().unpark()
}
}
let waker = Arc::new(Waker).into();
let mut cx = Context::from_waker(&waker);
let mut fut = Box::pin(fut);
loop {
match fut.as_mut().poll(&mut cx) {
Poll::Ready(_) => break,
Poll::Pending => thread::park(),
}
}
}
// just tests by whether or not this compiles
fn _pending_impl_all_auto_traits<T>() {
use std::panic::{RefUnwindSafe, UnwindSafe};
fn all_auto_traits<T: Send + Sync + Unpin + UnwindSafe + RefUnwindSafe>() {}
all_auto_traits::<std::future::Pending<T>>();
}
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