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FlattenUnordered: improve wakers behavior #2566

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Feb 6, 2022
Merged

FlattenUnordered: improve wakers behavior #2566

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24 changes: 16 additions & 8 deletions futures-util/src/stream/stream/flatten_unordered.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,11 +92,17 @@ impl SharedPollState {
let value = self
.state
.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |value| {
let next_value = value | to_poll;

// Waking process for this waker already started
if value & waking != NONE {
return None;
}
let mut next_value = value | to_poll;
// Only start the waking process if we're not in the polling phase and the stream isn't woken already
if value & (WOKEN | POLLING) == NONE {
Some(next_value | waking)
} else if next_value != value {
next_value |= waking;
}

if next_value != value {
Some(next_value)
} else {
None
Expand Down Expand Up @@ -141,11 +147,13 @@ impl SharedPollState {
fn stop_waking(&self, waking: u8) -> u8 {
self.state
.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |value| {
let next_value = value & !waking;

let mut next_value = value & !waking;
// Waker will be called only if the current waking state is the same as the specified waker state
if value & WAKING_ALL == waking {
Some(next_value | WOKEN)
} else if next_value != value {
next_value |= WOKEN;
}

if next_value != value {
Some(next_value)
} else {
None
Expand Down