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Fix new scheduler loop #747

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Merged
merged 1 commit into from
Apr 9, 2020
Merged

Fix new scheduler loop #747

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14 changes: 8 additions & 6 deletions src/rt/runtime.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -249,6 +249,8 @@ impl Machine {
continue;
}

let mut sched = rt.sched.lock().unwrap();

// One final check for available tasks while the scheduler is locked.
if let Some(task) = iter::repeat_with(|| self.find_task(rt))
.find(|s| !s.is_retry())
Expand All @@ -258,19 +260,19 @@ impl Machine {
continue;
}

let mut sched = rt.sched.lock().unwrap();

// If another thread is already blocked on the reactor, there is no point in keeping
// the current thread around since there is too little work to do.
if sched.polling {
thread::sleep(Duration::from_micros(10));
continue;
break;
}
Comment on lines +263 to 267
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@win-t win-t Apr 9, 2020 •
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I'm not sure, terminating the thread is a good idea, what will happen when the load is increasing? no new thread will be created

simple sleep like this will end up with single thread with no way to recover the worker thread

        task::spawn(async {
            loop {
                task::sleep(Duration::from_secs(1)).await;
                io::stdout().write_all(b"Hello World\n").await.unwrap();
            }
        })
        .await;

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@win-t win-t Apr 9, 2020 •
edited
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I want to bring back auto spawning thread here #740 (PR: #744) , but it's just as a fallback if the users forget to use spawn_blocking (or especially when they don't own full control of the code, like using a library)

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We can not go back to the sleep & continue, it regresses performance even further, so we need to find a better solution.

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The correct fix as far as I understand is to bring back the dynamic restarting of machines: #748


// Unlock the schedule poll the reactor until new I/O events arrive.
sched.polling = true;
drop(sched);

rt.reactor.poll(None).unwrap();

let mut sched = rt.sched.lock().unwrap();
// Lock the scheduler again and re-register the machine.
sched = rt.sched.lock().unwrap();
sched.polling = false;

runs = 0;
Expand Down