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Fixed deadlock in injection_queue_depth_multi_thread test #6916

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Fixed deadlock in injection_queue_depth_multi_thread test #6916

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66 changes: 39 additions & 27 deletions tokio/tests/rt_metrics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,8 @@
#![warn(rust_2018_idioms)]
#![cfg(all(feature = "full", not(target_os = "wasi"), target_has_atomic = "64"))]

use std::sync::{Arc, Barrier};
use std::sync::mpsc;
use std::time::Duration;
use tokio::runtime::Runtime;

#[test]
Expand Down Expand Up @@ -68,36 +69,47 @@ fn injection_queue_depth_multi_thread() {
let rt = threaded();
let metrics = rt.metrics();

let barrier1 = Arc::new(Barrier::new(3));
let barrier2 = Arc::new(Barrier::new(3));

// Spawn a task per runtime worker to block it.
for _ in 0..2 {
let barrier1 = barrier1.clone();
let barrier2 = barrier2.clone();
rt.spawn(async move {
barrier1.wait();
barrier2.wait();
});
}

barrier1.wait();

let mut fail: Option<String> = None;
for i in 0..10 {
let depth = metrics.injection_queue_depth();
if i != depth {
fail = Some(format!("{i} is not equal to {depth}"));
break;
'next_try: for _ in 0..10 {
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We usually do this kind of retrying by defining two functions, to separate out the concerns.

let (tx, rx) = mpsc::channel();

// Dropping _blocking_tasks will cause the blocking tasks to finish.
let _blocking_tasks: Vec<_> = (0..2)
.map(|_| {
let tx = tx.clone();
let (task, barrier) = mpsc::channel::<()>();

// Spawn a task per runtime worker to block it.
rt.spawn(async move {
tx.send(()).unwrap();
barrier.recv().ok();
});

task
})
.collect();

// Make sure both tasks are blocking the runtime so that we can
// deterministically fill up the injection queue with pending tasks.
//
// If this times out, we deadlocked the runtime (which can happen and is
// expected behaviour) and retry the test until we manage to either not
// deadlock the runtime or exhaust all tries, the latter causing the
// test to fail.
for _ in 0..2 {
if rx.recv_timeout(Duration::from_secs(1)).is_err() {
continue 'next_try;
}
}
rt.spawn(async {});
}

barrier2.wait();
for i in 0..10 {
assert_eq!(i, metrics.injection_queue_depth());
rt.spawn(async {});
}

if let Some(fail) = fail {
panic!("{fail}");
return;
}

panic!("runtime deadlocked each try");
}

fn current_thread() -> Runtime {
Expand Down
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