Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
runtime: avoid unnecessary polling of block_on future (#3582)
- Loading branch information
1 parent
345b29c
commit e6a9167
Showing
3 changed files
with
105 additions
and
2 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,82 @@ | ||
use crate::loom::sync::atomic::AtomicUsize; | ||
use crate::loom::sync::Arc; | ||
use crate::loom::thread; | ||
use crate::runtime::{Builder, Runtime}; | ||
use crate::sync::oneshot::{self, Receiver}; | ||
use crate::task; | ||
use std::future::Future; | ||
use std::pin::Pin; | ||
use std::sync::atomic::Ordering::{Acquire, Release}; | ||
use std::task::{Context, Poll}; | ||
|
||
fn assert_at_most_num_polls(rt: Arc<Runtime>, at_most_polls: usize) { | ||
let (tx, rx) = oneshot::channel(); | ||
let num_polls = Arc::new(AtomicUsize::new(0)); | ||
rt.spawn(async move { | ||
for _ in 0..12 { | ||
task::yield_now().await; | ||
} | ||
tx.send(()).unwrap(); | ||
}); | ||
|
||
rt.block_on(async { | ||
BlockedFuture { | ||
rx, | ||
num_polls: num_polls.clone(), | ||
} | ||
.await; | ||
}); | ||
|
||
let polls = num_polls.load(Acquire); | ||
assert!(polls <= at_most_polls); | ||
} | ||
|
||
#[test] | ||
fn block_on_num_polls() { | ||
loom::model(|| { | ||
// we expect at most 3 number of polls because there are | ||
// three points at which we poll the future. At any of these | ||
// points it can be ready: | ||
// | ||
// - when we fail to steal the parker and we block on a | ||
// notification that it is available. | ||
// | ||
// - when we steal the parker and we schedule the future | ||
// | ||
// - when the future is woken up and we have ran the max | ||
// number of tasks for the current tick or there are no | ||
// more tasks to run. | ||
// | ||
let at_most = 3; | ||
|
||
let rt1 = Arc::new(Builder::new_current_thread().build().unwrap()); | ||
let rt2 = rt1.clone(); | ||
let rt3 = rt1.clone(); | ||
|
||
let th1 = thread::spawn(move || assert_at_most_num_polls(rt1, at_most)); | ||
let th2 = thread::spawn(move || assert_at_most_num_polls(rt2, at_most)); | ||
let th3 = thread::spawn(move || assert_at_most_num_polls(rt3, at_most)); | ||
|
||
th1.join().unwrap(); | ||
th2.join().unwrap(); | ||
th3.join().unwrap(); | ||
}); | ||
} | ||
|
||
struct BlockedFuture { | ||
rx: Receiver<()>, | ||
num_polls: Arc<AtomicUsize>, | ||
} | ||
|
||
impl Future for BlockedFuture { | ||
type Output = (); | ||
|
||
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { | ||
self.num_polls.fetch_add(1, Release); | ||
|
||
match Pin::new(&mut self.rx).poll(cx) { | ||
Poll::Pending => Poll::Pending, | ||
_ => Poll::Ready(()), | ||
} | ||
} | ||
} |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -1,4 +1,5 @@ | ||
cfg_loom! { | ||
mod loom_basic_scheduler; | ||
mod loom_blocking; | ||
mod loom_oneshot; | ||
mod loom_pool; | ||
|