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Make the Waitlist responsible for calling wake #367

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53420cc
Drop a lock earlier
espindola Jul 24, 2025
02f3b7c
Convert the conn_return macro into a function
espindola Jul 24, 2025
4388a73
Refactor the waitlist to another module
espindola Aug 5, 2025
902c125
Make the Waitlist responsible for calling wake
espindola Aug 12, 2025
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2 changes: 1 addition & 1 deletion src/conn/pool/futures/disconnect_pool.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ use futures_core::ready;
use tokio::sync::mpsc::UnboundedSender;

use crate::{
conn::pool::{Inner, Pool, QUEUE_END_ID},
conn::pool::{waitlist::QUEUE_END_ID, Inner, Pool},
error::Error,
Conn,
};
Expand Down
2 changes: 1 addition & 1 deletion src/conn/pool/futures/get_conn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ use {

use crate::{
conn::{
pool::{Pool, QueueId},
pool::{waitlist::QueueId, Pool},
Conn,
},
error::*,
Expand Down
140 changes: 9 additions & 131 deletions src/conn/pool/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,17 +7,13 @@
// modified, or distributed except according to those terms.

use futures_util::FutureExt;
use keyed_priority_queue::KeyedPriorityQueue;
use tokio::sync::mpsc;

use std::{
borrow::Borrow,
cmp::Reverse,
collections::VecDeque,
hash::{Hash, Hasher},
str::FromStr,
sync::{atomic, Arc, Mutex},
task::{Context, Poll, Waker},
task::{Context, Poll},
time::{Duration, Instant},
};

Expand All @@ -29,12 +25,14 @@ use crate::{
};

pub use metrics::Metrics;
use waitlist::{QueueId, Waitlist};

mod recycler;
// this is a really unfortunate name for a module
pub mod futures;
mod metrics;
mod ttl_check_inerval;
mod waitlist;

/// Connection that is idling in the pool.
#[derive(Debug)]
Expand Down Expand Up @@ -104,86 +102,6 @@ impl Exchange {
}
}

#[derive(Default, Debug)]
struct Waitlist {
queue: KeyedPriorityQueue<QueuedWaker, QueueId>,
}

impl Waitlist {
/// Returns `true` if pushed.
fn push(&mut self, waker: Waker, queue_id: QueueId) -> bool {
// The documentation of Future::poll says:
// Note that on multiple calls to poll, only the Waker from
// the Context passed to the most recent call should be
// scheduled to receive a wakeup.
//
// But the the documentation of KeyedPriorityQueue::push says:
// Adds new element to queue if missing key or replace its
// priority if key exists. In second case doesn’t replace key.
//
// This means we have to remove first to have the most recent
// waker in the queue.
let occupied = self.remove(queue_id);
self.queue.push(QueuedWaker { queue_id, waker }, queue_id);
!occupied
}

fn pop(&mut self) -> Option<Waker> {
match self.queue.pop() {
Some((qw, _)) => Some(qw.waker),
None => None,
}
}

/// Returns `true` if removed.
fn remove(&mut self, id: QueueId) -> bool {
self.queue.remove(&id).is_some()
}

fn peek_id(&mut self) -> Option<QueueId> {
self.queue.peek().map(|(qw, _)| qw.queue_id)
}
}

const QUEUE_END_ID: QueueId = QueueId(Reverse(u64::MAX));

#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub(crate) struct QueueId(Reverse<u64>);

impl QueueId {
fn next() -> Self {
static NEXT_QUEUE_ID: atomic::AtomicU64 = atomic::AtomicU64::new(0);
let id = NEXT_QUEUE_ID.fetch_add(1, atomic::Ordering::SeqCst);
QueueId(Reverse(id))
}
}

#[derive(Debug)]
struct QueuedWaker {
queue_id: QueueId,
waker: Waker,
}

impl Eq for QueuedWaker {}

impl Borrow<QueueId> for QueuedWaker {
fn borrow(&self) -> &QueueId {
&self.queue_id
}
}

impl PartialEq for QueuedWaker {
fn eq(&self, other: &Self) -> bool {
self.queue_id == other.queue_id
}
}

impl Hash for QueuedWaker {
fn hash<H: Hasher>(&self, state: &mut H) {
self.queue_id.hash(state)
}
}

/// Connection pool data.
#[derive(Debug)]
pub struct Inner {
Expand Down Expand Up @@ -310,9 +228,7 @@ impl Pool {
.connection_count
.store(exchange.exist, atomic::Ordering::Relaxed);
// we just enabled the creation of a new connection!
if let Some(w) = exchange.waiting.pop() {
w.wake();
}
exchange.waiting.wake();
}

/// Poll the pool for an available connection.
Expand Down Expand Up @@ -474,20 +390,16 @@ mod test {
use waker_fn::waker_fn;

use std::{
cmp::Reverse,
future::Future,
pin::pin,
sync::{Arc, OnceLock},
task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
task::{Context, Poll},
time::Duration,
};

use crate::{
conn::pool::{Pool, QueueId, Waitlist, QUEUE_END_ID},
opts::PoolOpts,
prelude::*,
test_misc::get_opts,
PoolConstraints, Row, TxOpts, Value,
conn::pool::Pool, opts::PoolOpts, prelude::*, test_misc::get_opts, PoolConstraints, Row,
TxOpts, Value,
};

macro_rules! conn_ex_field {
Expand Down Expand Up @@ -1016,7 +928,7 @@ mod test {
}
drop(only_conn);

assert_eq!(0, pool.inner.exchange.lock().unwrap().waiting.queue.len());
assert_eq!(0, pool.inner.exchange.lock().unwrap().waiting.len());
// metrics should catch up with waiting queue (see #335)
assert_eq!(
0,
Expand Down Expand Up @@ -1070,40 +982,6 @@ mod test {
Ok(())
}

#[test]
fn waitlist_integrity() {
const DATA: *const () = &();
const NOOP_CLONE_FN: unsafe fn(*const ()) -> RawWaker = |_| RawWaker::new(DATA, &RW_VTABLE);
const NOOP_FN: unsafe fn(*const ()) = |_| {};
static RW_VTABLE: RawWakerVTable =
RawWakerVTable::new(NOOP_CLONE_FN, NOOP_FN, NOOP_FN, NOOP_FN);
let w = unsafe { Waker::from_raw(RawWaker::new(DATA, &RW_VTABLE)) };

let mut waitlist = Waitlist::default();
assert_eq!(0, waitlist.queue.len());

waitlist.push(w.clone(), QueueId(Reverse(4)));
waitlist.push(w.clone(), QueueId(Reverse(2)));
waitlist.push(w.clone(), QueueId(Reverse(8)));
waitlist.push(w.clone(), QUEUE_END_ID);
waitlist.push(w.clone(), QueueId(Reverse(10)));

waitlist.remove(QueueId(Reverse(8)));

assert_eq!(4, waitlist.queue.len());

let (_, id) = waitlist.queue.pop().unwrap();
assert_eq!(2, id.0 .0);
let (_, id) = waitlist.queue.pop().unwrap();
assert_eq!(4, id.0 .0);
let (_, id) = waitlist.queue.pop().unwrap();
assert_eq!(10, id.0 .0);
let (_, id) = waitlist.queue.pop().unwrap();
assert_eq!(QUEUE_END_ID, id);

assert_eq!(0, waitlist.queue.len());
}

#[tokio::test]
async fn check_absolute_connection_ttl() -> super::Result<()> {
let constraints = PoolConstraints::new(1, 3).unwrap();
Expand Down Expand Up @@ -1185,7 +1063,7 @@ mod test {

let queue_len = || {
let exchange = pool.inner.exchange.lock().unwrap();
exchange.waiting.queue.len()
exchange.waiting.len()
};

// Get a connection, so we know the next futures will be
Expand Down
89 changes: 40 additions & 49 deletions src/conn/pool/recycler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,36 @@ impl Recycler {
eof: false,
}
}

fn conn_return(&mut self, conn: Conn, pool_is_closed: bool) {
let mut exchange = self.inner.exchange.lock().unwrap();
if pool_is_closed || exchange.available.len() >= self.pool_opts.active_bound() {
drop(exchange);
self.inner
.metrics
.discarded_superfluous_connection
.fetch_add(1, Ordering::Relaxed);
self.discard.push(conn.close_conn().boxed());
} else {
self.inner
.metrics
.connection_returned_to_pool
.fetch_add(1, Ordering::Relaxed);
#[cfg(feature = "hdrhistogram")]
self.inner
.metrics
.connection_active_duration
.lock()
.unwrap()
.saturating_record(conn.inner.active_since.elapsed().as_micros() as u64);
exchange.available.push_back(conn.into());
self.inner
.metrics
.connections_in_pool
.store(exchange.available.len(), Ordering::Relaxed);
exchange.waiting.wake();
}
}
}

impl Future for Recycler {
Expand All @@ -62,44 +92,6 @@ impl Future for Recycler {
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut close = self.inner.close.load(Ordering::Acquire);

macro_rules! conn_return {
($self:ident, $conn:ident, $pool_is_closed: expr) => {{
let mut exchange = $self.inner.exchange.lock().unwrap();
if $pool_is_closed || exchange.available.len() >= $self.pool_opts.active_bound() {
drop(exchange);
$self
.inner
.metrics
.discarded_superfluous_connection
.fetch_add(1, Ordering::Relaxed);
$self.discard.push($conn.close_conn().boxed());
} else {
$self
.inner
.metrics
.connection_returned_to_pool
.fetch_add(1, Ordering::Relaxed);
#[cfg(feature = "hdrhistogram")]
$self
.inner
.metrics
.connection_active_duration
.lock()
.unwrap()
.saturating_record($conn.inner.active_since.elapsed().as_micros() as u64);
exchange.available.push_back($conn.into());
$self
.inner
.metrics
.connections_in_pool
.store(exchange.available.len(), Ordering::Relaxed);
if let Some(w) = exchange.waiting.pop() {
w.wake();
}
}
}};
}

macro_rules! conn_decision {
($self:ident, $conn:ident) => {
if $conn.inner.stream.is_none() || $conn.inner.disconnected {
Expand Down Expand Up @@ -132,7 +124,7 @@ impl Future for Recycler {
.fetch_add(1, Ordering::Relaxed);
$self.reset.push($conn.reset_for_pool().boxed());
} else {
conn_return!($self, $conn, false);
$self.conn_return($conn, false);
}
};
}
Expand Down Expand Up @@ -165,9 +157,12 @@ impl Future for Recycler {

// if we've been asked to close, reclaim any idle connections
if close || self.eof {
while let Some(IdlingConn { conn, .. }) =
self.inner.exchange.lock().unwrap().available.pop_front()
{
loop {
let Some(IdlingConn { conn, .. }) =
self.inner.exchange.lock().unwrap().available.pop_front()
else {
break;
};
assert!(conn.inner.pool.is_none());
conn_decision!(self, conn);
}
Expand Down Expand Up @@ -199,7 +194,7 @@ impl Future for Recycler {
loop {
match Pin::new(&mut self.reset).poll_next(cx) {
Poll::Pending | Poll::Ready(None) => break,
Poll::Ready(Some(Ok(conn))) => conn_return!(self, conn, close),
Poll::Ready(Some(Ok(conn))) => self.conn_return(conn, close),
Poll::Ready(Some(Err(e))) => {
// an error during reset.
// replace with a new connection
Expand Down Expand Up @@ -247,9 +242,7 @@ impl Future for Recycler {
.connection_count
.store(exchange.exist, Ordering::Relaxed);
for _ in 0..self.discarded {
if let Some(w) = exchange.waiting.pop() {
w.wake();
}
exchange.waiting.wake();
}
drop(exchange);
self.discarded = 0;
Expand Down Expand Up @@ -285,9 +278,7 @@ impl Future for Recycler {
if self.inner.closed.load(Ordering::Acquire) {
// `DisconnectPool` might still wait to be woken up.
let mut exchange = self.inner.exchange.lock().unwrap();
while let Some(w) = exchange.waiting.pop() {
w.wake();
}
while exchange.waiting.wake() {}
// we're about to exit, so there better be no outstanding connections
assert_eq!(exchange.exist, 0);
assert_eq!(exchange.available.len(), 0);
Expand Down
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