Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1044 insertions, 0 deletions

diff --git a/third_party/rust/hyper/src/client/pool.rs b/third_party/rust/hyper/src/client/pool.rs
new file mode 100644
index 0000000000..b9772d688d
--- /dev/null
+++ b/third_party/rust/hyper/src/client/pool.rs
@@ -0,0 +1,1044 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+use std::error::Error as StdError;
+use std::fmt;
+use std::ops::{Deref, DerefMut};
+use std::sync::{Arc, Mutex, Weak};
+
+#[cfg(not(feature = "runtime"))]
+use std::time::{Duration, Instant};
+
+use futures_channel::oneshot;
+#[cfg(feature = "runtime")]
+use tokio::time::{Duration, Instant, Interval};
+use tracing::{debug, trace};
+
+use super::client::Ver;
+use crate::common::{exec::Exec, task, Future, Pin, Poll, Unpin};
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Pool<T> {
+    // If the pool is disabled, this is None.
+    inner: Option<Arc<Mutex<PoolInner<T>>>>,
+}
+
+// Before using a pooled connection, make sure the sender is not dead.
+//
+// This is a trait to allow the `client::pool::tests` to work for `i32`.
+//
+// See https://github.com/hyperium/hyper/issues/1429
+pub(super) trait Poolable: Unpin + Send + Sized + 'static {
+    fn is_open(&self) -> bool;
+    /// Reserve this connection.
+    ///
+    /// Allows for HTTP/2 to return a shared reservation.
+    fn reserve(self) -> Reservation<Self>;
+    fn can_share(&self) -> bool;
+}
+
+/// When checking out a pooled connection, it might be that the connection
+/// only supports a single reservation, or it might be usable for many.
+///
+/// Specifically, HTTP/1 requires a unique reservation, but HTTP/2 can be
+/// used for multiple requests.
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) enum Reservation<T> {
+    /// This connection could be used multiple times, the first one will be
+    /// reinserted into the `idle` pool, and the second will be given to
+    /// the `Checkout`.
+    #[cfg(feature = "http2")]
+    Shared(T, T),
+    /// This connection requires unique access. It will be returned after
+    /// use is complete.
+    Unique(T),
+}
+
+/// Simple type alias in case the key type needs to be adjusted.
+pub(super) type Key = (http::uri::Scheme, http::uri::Authority); //Arc<String>;
+
+struct PoolInner<T> {
+    // A flag that a connection is being established, and the connection
+    // should be shared. This prevents making multiple HTTP/2 connections
+    // to the same host.
+    connecting: HashSet<Key>,
+    // These are internal Conns sitting in the event loop in the KeepAlive
+    // state, waiting to receive a new Request to send on the socket.
+    idle: HashMap<Key, Vec<Idle<T>>>,
+    max_idle_per_host: usize,
+    // These are outstanding Checkouts that are waiting for a socket to be
+    // able to send a Request one. This is used when "racing" for a new
+    // connection.
+    //
+    // The Client starts 2 tasks, 1 to connect a new socket, and 1 to wait
+    // for the Pool to receive an idle Conn. When a Conn becomes idle,
+    // this list is checked for any parked Checkouts, and tries to notify
+    // them that the Conn could be used instead of waiting for a brand new
+    // connection.
+    waiters: HashMap<Key, VecDeque<oneshot::Sender<T>>>,
+    // A oneshot channel is used to allow the interval to be notified when
+    // the Pool completely drops. That way, the interval can cancel immediately.
+    #[cfg(feature = "runtime")]
+    idle_interval_ref: Option<oneshot::Sender<crate::common::Never>>,
+    #[cfg(feature = "runtime")]
+    exec: Exec,
+    timeout: Option<Duration>,
+}
+
+// This is because `Weak::new()` *allocates* space for `T`, even if it
+// doesn't need it!
+struct WeakOpt<T>(Option<Weak<T>>);
+
+#[derive(Clone, Copy, Debug)]
+pub(super) struct Config {
+    pub(super) idle_timeout: Option<Duration>,
+    pub(super) max_idle_per_host: usize,
+}
+
+impl Config {
+    pub(super) fn is_enabled(&self) -> bool {
+        self.max_idle_per_host > 0
+    }
+}
+
+impl<T> Pool<T> {
+    pub(super) fn new(config: Config, __exec: &Exec) -> Pool<T> {
+        let inner = if config.is_enabled() {
+            Some(Arc::new(Mutex::new(PoolInner {
+                connecting: HashSet::new(),
+                idle: HashMap::new(),
+                #[cfg(feature = "runtime")]
+                idle_interval_ref: None,
+                max_idle_per_host: config.max_idle_per_host,
+                waiters: HashMap::new(),
+                #[cfg(feature = "runtime")]
+                exec: __exec.clone(),
+                timeout: config.idle_timeout,
+            })))
+        } else {
+            None
+        };
+
+        Pool { inner }
+    }
+
+    fn is_enabled(&self) -> bool {
+        self.inner.is_some()
+    }
+
+    #[cfg(test)]
+    pub(super) fn no_timer(&self) {
+        // Prevent an actual interval from being created for this pool...
+        #[cfg(feature = "runtime")]
+        {
+            let mut inner = self.inner.as_ref().unwrap().lock().unwrap();
+            assert!(inner.idle_interval_ref.is_none(), "timer already spawned");
+            let (tx, _) = oneshot::channel();
+            inner.idle_interval_ref = Some(tx);
+        }
+    }
+}
+
+impl<T: Poolable> Pool<T> {
+    /// Returns a `Checkout` which is a future that resolves if an idle
+    /// connection becomes available.
+    pub(super) fn checkout(&self, key: Key) -> Checkout<T> {
+        Checkout {
+            key,
+            pool: self.clone(),
+            waiter: None,
+        }
+    }
+
+    /// Ensure that there is only ever 1 connecting task for HTTP/2
+    /// connections. This does nothing for HTTP/1.
+    pub(super) fn connecting(&self, key: &Key, ver: Ver) -> Option<Connecting<T>> {
+        if ver == Ver::Http2 {
+            if let Some(ref enabled) = self.inner {
+                let mut inner = enabled.lock().unwrap();
+                return if inner.connecting.insert(key.clone()) {
+                    let connecting = Connecting {
+                        key: key.clone(),
+                        pool: WeakOpt::downgrade(enabled),
+                    };
+                    Some(connecting)
+                } else {
+                    trace!("HTTP/2 connecting already in progress for {:?}", key);
+                    None
+                };
+            }
+        }
+
+        // else
+        Some(Connecting {
+            key: key.clone(),
+            // in HTTP/1's case, there is never a lock, so we don't
+            // need to do anything in Drop.
+            pool: WeakOpt::none(),
+        })
+    }
+
+    #[cfg(test)]
+    fn locked(&self) -> std::sync::MutexGuard<'_, PoolInner<T>> {
+        self.inner.as_ref().expect("enabled").lock().expect("lock")
+    }
+
+    /* Used in client/tests.rs...
+    #[cfg(feature = "runtime")]
+    #[cfg(test)]
+    pub(super) fn h1_key(&self, s: &str) -> Key {
+        Arc::new(s.to_string())
+    }
+
+    #[cfg(feature = "runtime")]
+    #[cfg(test)]
+    pub(super) fn idle_count(&self, key: &Key) -> usize {
+        self
+            .locked()
+            .idle
+            .get(key)
+            .map(|list| list.len())
+            .unwrap_or(0)
+    }
+    */
+
+    pub(super) fn pooled(
+        &self,
+        #[cfg_attr(not(feature = "http2"), allow(unused_mut))] mut connecting: Connecting<T>,
+        value: T,
+    ) -> Pooled<T> {
+        let (value, pool_ref) = if let Some(ref enabled) = self.inner {
+            match value.reserve() {
+                #[cfg(feature = "http2")]
+                Reservation::Shared(to_insert, to_return) => {
+                    let mut inner = enabled.lock().unwrap();
+                    inner.put(connecting.key.clone(), to_insert, enabled);
+                    // Do this here instead of Drop for Connecting because we
+                    // already have a lock, no need to lock the mutex twice.
+                    inner.connected(&connecting.key);
+                    // prevent the Drop of Connecting from repeating inner.connected()
+                    connecting.pool = WeakOpt::none();
+
+                    // Shared reservations don't need a reference to the pool,
+                    // since the pool always keeps a copy.
+                    (to_return, WeakOpt::none())
+                }
+                Reservation::Unique(value) => {
+                    // Unique reservations must take a reference to the pool
+                    // since they hope to reinsert once the reservation is
+                    // completed
+                    (value, WeakOpt::downgrade(enabled))
+                }
+            }
+        } else {
+            // If pool is not enabled, skip all the things...
+
+            // The Connecting should have had no pool ref
+            debug_assert!(connecting.pool.upgrade().is_none());
+
+            (value, WeakOpt::none())
+        };
+        Pooled {
+            key: connecting.key.clone(),
+            is_reused: false,
+            pool: pool_ref,
+            value: Some(value),
+        }
+    }
+
+    fn reuse(&self, key: &Key, value: T) -> Pooled<T> {
+        debug!("reuse idle connection for {:?}", key);
+        // TODO: unhack this
+        // In Pool::pooled(), which is used for inserting brand new connections,
+        // there's some code that adjusts the pool reference taken depending
+        // on if the Reservation can be shared or is unique. By the time
+        // reuse() is called, the reservation has already been made, and
+        // we just have the final value, without knowledge of if this is
+        // unique or shared. So, the hack is to just assume Ver::Http2 means
+        // shared... :(
+        let mut pool_ref = WeakOpt::none();
+        if !value.can_share() {
+            if let Some(ref enabled) = self.inner {
+                pool_ref = WeakOpt::downgrade(enabled);
+            }
+        }
+
+        Pooled {
+            is_reused: true,
+            key: key.clone(),
+            pool: pool_ref,
+            value: Some(value),
+        }
+    }
+}
+
+/// Pop off this list, looking for a usable connection that hasn't expired.
+struct IdlePopper<'a, T> {
+    key: &'a Key,
+    list: &'a mut Vec<Idle<T>>,
+}
+
+impl<'a, T: Poolable + 'a> IdlePopper<'a, T> {
+    fn pop(self, expiration: &Expiration) -> Option<Idle<T>> {
+        while let Some(entry) = self.list.pop() {
+            // If the connection has been closed, or is older than our idle
+            // timeout, simply drop it and keep looking...
+            if !entry.value.is_open() {
+                trace!("removing closed connection for {:?}", self.key);
+                continue;
+            }
+            // TODO: Actually, since the `idle` list is pushed to the end always,
+            // that would imply that if *this* entry is expired, then anything
+            // "earlier" in the list would *have* to be expired also... Right?
+            //
+            // In that case, we could just break out of the loop and drop the
+            // whole list...
+            if expiration.expires(entry.idle_at) {
+                trace!("removing expired connection for {:?}", self.key);
+                continue;
+            }
+
+            let value = match entry.value.reserve() {
+                #[cfg(feature = "http2")]
+                Reservation::Shared(to_reinsert, to_checkout) => {
+                    self.list.push(Idle {
+                        idle_at: Instant::now(),
+                        value: to_reinsert,
+                    });
+                    to_checkout
+                }
+                Reservation::Unique(unique) => unique,
+            };
+
+            return Some(Idle {
+                idle_at: entry.idle_at,
+                value,
+            });
+        }
+
+        None
+    }
+}
+
+impl<T: Poolable> PoolInner<T> {
+    fn put(&mut self, key: Key, value: T, __pool_ref: &Arc<Mutex<PoolInner<T>>>) {
+        if value.can_share() && self.idle.contains_key(&key) {
+            trace!("put; existing idle HTTP/2 connection for {:?}", key);
+            return;
+        }
+        trace!("put; add idle connection for {:?}", key);
+        let mut remove_waiters = false;
+        let mut value = Some(value);
+        if let Some(waiters) = self.waiters.get_mut(&key) {
+            while let Some(tx) = waiters.pop_front() {
+                if !tx.is_canceled() {
+                    let reserved = value.take().expect("value already sent");
+                    let reserved = match reserved.reserve() {
+                        #[cfg(feature = "http2")]
+                        Reservation::Shared(to_keep, to_send) => {
+                            value = Some(to_keep);
+                            to_send
+                        }
+                        Reservation::Unique(uniq) => uniq,
+                    };
+                    match tx.send(reserved) {
+                        Ok(()) => {
+                            if value.is_none() {
+                                break;
+                            } else {
+                                continue;
+                            }
+                        }
+                        Err(e) => {
+                            value = Some(e);
+                        }
+                    }
+                }
+
+                trace!("put; removing canceled waiter for {:?}", key);
+            }
+            remove_waiters = waiters.is_empty();
+        }
+        if remove_waiters {
+            self.waiters.remove(&key);
+        }
+
+        match value {
+            Some(value) => {
+                // borrow-check scope...
+                {
+                    let idle_list = self.idle.entry(key.clone()).or_insert_with(Vec::new);
+                    if self.max_idle_per_host <= idle_list.len() {
+                        trace!("max idle per host for {:?}, dropping connection", key);
+                        return;
+                    }
+
+                    debug!("pooling idle connection for {:?}", key);
+                    idle_list.push(Idle {
+                        value,
+                        idle_at: Instant::now(),
+                    });
+                }
+
+                #[cfg(feature = "runtime")]
+                {
+                    self.spawn_idle_interval(__pool_ref);
+                }
+            }
+            None => trace!("put; found waiter for {:?}", key),
+        }
+    }
+
+    /// A `Connecting` task is complete. Not necessarily successfully,
+    /// but the lock is going away, so clean up.
+    fn connected(&mut self, key: &Key) {
+        let existed = self.connecting.remove(key);
+        debug_assert!(existed, "Connecting dropped, key not in pool.connecting");
+        // cancel any waiters. if there are any, it's because
+        // this Connecting task didn't complete successfully.
+        // those waiters would never receive a connection.
+        self.waiters.remove(key);
+    }
+
+    #[cfg(feature = "runtime")]
+    fn spawn_idle_interval(&mut self, pool_ref: &Arc<Mutex<PoolInner<T>>>) {
+        let (dur, rx) = {
+            if self.idle_interval_ref.is_some() {
+                return;
+            }
+
+            if let Some(dur) = self.timeout {
+                let (tx, rx) = oneshot::channel();
+                self.idle_interval_ref = Some(tx);
+                (dur, rx)
+            } else {
+                return;
+            }
+        };
+
+        let interval = IdleTask {
+            interval: tokio::time::interval(dur),
+            pool: WeakOpt::downgrade(pool_ref),
+            pool_drop_notifier: rx,
+        };
+
+        self.exec.execute(interval);
+    }
+}
+
+impl<T> PoolInner<T> {
+    /// Any `FutureResponse`s that were created will have made a `Checkout`,
+    /// and possibly inserted into the pool that it is waiting for an idle
+    /// connection. If a user ever dropped that future, we need to clean out
+    /// those parked senders.
+    fn clean_waiters(&mut self, key: &Key) {
+        let mut remove_waiters = false;
+        if let Some(waiters) = self.waiters.get_mut(key) {
+            waiters.retain(|tx| !tx.is_canceled());
+            remove_waiters = waiters.is_empty();
+        }
+        if remove_waiters {
+            self.waiters.remove(key);
+        }
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl<T: Poolable> PoolInner<T> {
+    /// This should *only* be called by the IdleTask
+    fn clear_expired(&mut self) {
+        let dur = self.timeout.expect("interval assumes timeout");
+
+        let now = Instant::now();
+        //self.last_idle_check_at = now;
+
+        self.idle.retain(|key, values| {
+            values.retain(|entry| {
+                if !entry.value.is_open() {
+                    trace!("idle interval evicting closed for {:?}", key);
+                    return false;
+                }
+
+                // Avoid `Instant::sub` to avoid issues like rust-lang/rust#86470.
+                if now.saturating_duration_since(entry.idle_at) > dur {
+                    trace!("idle interval evicting expired for {:?}", key);
+                    return false;
+                }
+
+                // Otherwise, keep this value...
+                true
+            });
+
+            // returning false evicts this key/val
+            !values.is_empty()
+        });
+    }
+}
+
+impl<T> Clone for Pool<T> {
+    fn clone(&self) -> Pool<T> {
+        Pool {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+/// A wrapped poolable value that tries to reinsert to the Pool on Drop.
+// Note: The bounds `T: Poolable` is needed for the Drop impl.
+pub(super) struct Pooled<T: Poolable> {
+    value: Option<T>,
+    is_reused: bool,
+    key: Key,
+    pool: WeakOpt<Mutex<PoolInner<T>>>,
+}
+
+impl<T: Poolable> Pooled<T> {
+    pub(super) fn is_reused(&self) -> bool {
+        self.is_reused
+    }
+
+    pub(super) fn is_pool_enabled(&self) -> bool {
+        self.pool.0.is_some()
+    }
+
+    fn as_ref(&self) -> &T {
+        self.value.as_ref().expect("not dropped")
+    }
+
+    fn as_mut(&mut self) -> &mut T {
+        self.value.as_mut().expect("not dropped")
+    }
+}
+
+impl<T: Poolable> Deref for Pooled<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.as_ref()
+    }
+}
+
+impl<T: Poolable> DerefMut for Pooled<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.as_mut()
+    }
+}
+
+impl<T: Poolable> Drop for Pooled<T> {
+    fn drop(&mut self) {
+        if let Some(value) = self.value.take() {
+            if !value.is_open() {
+                // If we *already* know the connection is done here,
+                // it shouldn't be re-inserted back into the pool.
+                return;
+            }
+
+            if let Some(pool) = self.pool.upgrade() {
+                if let Ok(mut inner) = pool.lock() {
+                    inner.put(self.key.clone(), value, &pool);
+                }
+            } else if !value.can_share() {
+                trace!("pool dropped, dropping pooled ({:?})", self.key);
+            }
+            // Ver::Http2 is already in the Pool (or dead), so we wouldn't
+            // have an actual reference to the Pool.
+        }
+    }
+}
+
+impl<T: Poolable> fmt::Debug for Pooled<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Pooled").field("key", &self.key).finish()
+    }
+}
+
+struct Idle<T> {
+    idle_at: Instant,
+    value: T,
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Checkout<T> {
+    key: Key,
+    pool: Pool<T>,
+    waiter: Option<oneshot::Receiver<T>>,
+}
+
+#[derive(Debug)]
+pub(super) struct CheckoutIsClosedError;
+
+impl StdError for CheckoutIsClosedError {}
+
+impl fmt::Display for CheckoutIsClosedError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("checked out connection was closed")
+    }
+}
+
+impl<T: Poolable> Checkout<T> {
+    fn poll_waiter(
+        &mut self,
+        cx: &mut task::Context<'_>,
+    ) -> Poll<Option<crate::Result<Pooled<T>>>> {
+        if let Some(mut rx) = self.waiter.take() {
+            match Pin::new(&mut rx).poll(cx) {
+                Poll::Ready(Ok(value)) => {
+                    if value.is_open() {
+                        Poll::Ready(Some(Ok(self.pool.reuse(&self.key, value))))
+                    } else {
+                        Poll::Ready(Some(Err(
+                            crate::Error::new_canceled().with(CheckoutIsClosedError)
+                        )))
+                    }
+                }
+                Poll::Pending => {
+                    self.waiter = Some(rx);
+                    Poll::Pending
+                }
+                Poll::Ready(Err(_canceled)) => Poll::Ready(Some(Err(
+                    crate::Error::new_canceled().with("request has been canceled")
+                ))),
+            }
+        } else {
+            Poll::Ready(None)
+        }
+    }
+
+    fn checkout(&mut self, cx: &mut task::Context<'_>) -> Option<Pooled<T>> {
+        let entry = {
+            let mut inner = self.pool.inner.as_ref()?.lock().unwrap();
+            let expiration = Expiration::new(inner.timeout);
+            let maybe_entry = inner.idle.get_mut(&self.key).and_then(|list| {
+                trace!("take? {:?}: expiration = {:?}", self.key, expiration.0);
+                // A block to end the mutable borrow on list,
+                // so the map below can check is_empty()
+                {
+                    let popper = IdlePopper {
+                        key: &self.key,
+                        list,
+                    };
+                    popper.pop(&expiration)
+                }
+                .map(|e| (e, list.is_empty()))
+            });
+
+            let (entry, empty) = if let Some((e, empty)) = maybe_entry {
+                (Some(e), empty)
+            } else {
+                // No entry found means nuke the list for sure.
+                (None, true)
+            };
+            if empty {
+                //TODO: This could be done with the HashMap::entry API instead.
+                inner.idle.remove(&self.key);
+            }
+
+            if entry.is_none() && self.waiter.is_none() {
+                let (tx, mut rx) = oneshot::channel();
+                trace!("checkout waiting for idle connection: {:?}", self.key);
+                inner
+                    .waiters
+                    .entry(self.key.clone())
+                    .or_insert_with(VecDeque::new)
+                    .push_back(tx);
+
+                // register the waker with this oneshot
+                assert!(Pin::new(&mut rx).poll(cx).is_pending());
+                self.waiter = Some(rx);
+            }
+
+            entry
+        };
+
+        entry.map(|e| self.pool.reuse(&self.key, e.value))
+    }
+}
+
+impl<T: Poolable> Future for Checkout<T> {
+    type Output = crate::Result<Pooled<T>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        if let Some(pooled) = ready!(self.poll_waiter(cx)?) {
+            return Poll::Ready(Ok(pooled));
+        }
+
+        if let Some(pooled) = self.checkout(cx) {
+            Poll::Ready(Ok(pooled))
+        } else if !self.pool.is_enabled() {
+            Poll::Ready(Err(crate::Error::new_canceled().with("pool is disabled")))
+        } else {
+            // There's a new waiter, already registered in self.checkout()
+            debug_assert!(self.waiter.is_some());
+            Poll::Pending
+        }
+    }
+}
+
+impl<T> Drop for Checkout<T> {
+    fn drop(&mut self) {
+        if self.waiter.take().is_some() {
+            trace!("checkout dropped for {:?}", self.key);
+            if let Some(Ok(mut inner)) = self.pool.inner.as_ref().map(|i| i.lock()) {
+                inner.clean_waiters(&self.key);
+            }
+        }
+    }
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+#[allow(missing_debug_implementations)]
+pub(super) struct Connecting<T: Poolable> {
+    key: Key,
+    pool: WeakOpt<Mutex<PoolInner<T>>>,
+}
+
+impl<T: Poolable> Connecting<T> {
+    pub(super) fn alpn_h2(self, pool: &Pool<T>) -> Option<Self> {
+        debug_assert!(
+            self.pool.0.is_none(),
+            "Connecting::alpn_h2 but already Http2"
+        );
+
+        pool.connecting(&self.key, Ver::Http2)
+    }
+}
+
+impl<T: Poolable> Drop for Connecting<T> {
+    fn drop(&mut self) {
+        if let Some(pool) = self.pool.upgrade() {
+            // No need to panic on drop, that could abort!
+            if let Ok(mut inner) = pool.lock() {
+                inner.connected(&self.key);
+            }
+        }
+    }
+}
+
+struct Expiration(Option<Duration>);
+
+impl Expiration {
+    fn new(dur: Option<Duration>) -> Expiration {
+        Expiration(dur)
+    }
+
+    fn expires(&self, instant: Instant) -> bool {
+        match self.0 {
+            // Avoid `Instant::elapsed` to avoid issues like rust-lang/rust#86470.
+            Some(timeout) => Instant::now().saturating_duration_since(instant) > timeout,
+            None => false,
+        }
+    }
+}
+
+#[cfg(feature = "runtime")]
+pin_project_lite::pin_project! {
+    struct IdleTask<T> {
+        #[pin]
+        interval: Interval,
+        pool: WeakOpt<Mutex<PoolInner<T>>>,
+        // This allows the IdleTask to be notified as soon as the entire
+        // Pool is fully dropped, and shutdown. This channel is never sent on,
+        // but Err(Canceled) will be received when the Pool is dropped.
+        #[pin]
+        pool_drop_notifier: oneshot::Receiver<crate::common::Never>,
+    }
+}
+
+#[cfg(feature = "runtime")]
+impl<T: Poolable + 'static> Future for IdleTask<T> {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            match this.pool_drop_notifier.as_mut().poll(cx) {
+                Poll::Ready(Ok(n)) => match n {},
+                Poll::Pending => (),
+                Poll::Ready(Err(_canceled)) => {
+                    trace!("pool closed, canceling idle interval");
+                    return Poll::Ready(());
+                }
+            }
+
+            ready!(this.interval.as_mut().poll_tick(cx));
+
+            if let Some(inner) = this.pool.upgrade() {
+                if let Ok(mut inner) = inner.lock() {
+                    trace!("idle interval checking for expired");
+                    inner.clear_expired();
+                    continue;
+                }
+            }
+            return Poll::Ready(());
+        }
+    }
+}
+
+impl<T> WeakOpt<T> {
+    fn none() -> Self {
+        WeakOpt(None)
+    }
+
+    fn downgrade(arc: &Arc<T>) -> Self {
+        WeakOpt(Some(Arc::downgrade(arc)))
+    }
+
+    fn upgrade(&self) -> Option<Arc<T>> {
+        self.0.as_ref().and_then(Weak::upgrade)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::task::Poll;
+    use std::time::Duration;
+
+    use super::{Connecting, Key, Pool, Poolable, Reservation, WeakOpt};
+    use crate::common::{exec::Exec, task, Future, Pin};
+
+    /// Test unique reservations.
+    #[derive(Debug, PartialEq, Eq)]
+    struct Uniq<T>(T);
+
+    impl<T: Send + 'static + Unpin> Poolable for Uniq<T> {
+        fn is_open(&self) -> bool {
+            true
+        }
+
+        fn reserve(self) -> Reservation<Self> {
+            Reservation::Unique(self)
+        }
+
+        fn can_share(&self) -> bool {
+            false
+        }
+    }
+
+    fn c<T: Poolable>(key: Key) -> Connecting<T> {
+        Connecting {
+            key,
+            pool: WeakOpt::none(),
+        }
+    }
+
+    fn host_key(s: &str) -> Key {
+        (http::uri::Scheme::HTTP, s.parse().expect("host key"))
+    }
+
+    fn pool_no_timer<T>() -> Pool<T> {
+        pool_max_idle_no_timer(::std::usize::MAX)
+    }
+
+    fn pool_max_idle_no_timer<T>(max_idle: usize) -> Pool<T> {
+        let pool = Pool::new(
+            super::Config {
+                idle_timeout: Some(Duration::from_millis(100)),
+                max_idle_per_host: max_idle,
+            },
+            &Exec::Default,
+        );
+        pool.no_timer();
+        pool
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_smoke() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        drop(pooled);
+
+        match pool.checkout(key).await {
+            Ok(pooled) => assert_eq!(*pooled, Uniq(41)),
+            Err(_) => panic!("not ready"),
+        };
+    }
+
+    /// Helper to check if the future is ready after polling once.
+    struct PollOnce<'a, F>(&'a mut F);
+
+    impl<F, T, U> Future for PollOnce<'_, F>
+    where
+        F: Future<Output = Result<T, U>> + Unpin,
+    {
+        type Output = Option<()>;
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+            match Pin::new(&mut self.0).poll(cx) {
+                Poll::Ready(Ok(_)) => Poll::Ready(Some(())),
+                Poll::Ready(Err(_)) => Poll::Ready(Some(())),
+                Poll::Pending => Poll::Ready(None),
+            }
+        }
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_returns_none_if_expired() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        drop(pooled);
+        tokio::time::sleep(pool.locked().timeout.unwrap()).await;
+        let mut checkout = pool.checkout(key);
+        let poll_once = PollOnce(&mut checkout);
+        let is_not_ready = poll_once.await.is_none();
+        assert!(is_not_ready);
+    }
+
+    #[cfg(feature = "runtime")]
+    #[tokio::test]
+    async fn test_pool_checkout_removes_expired() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(3)
+        );
+        tokio::time::sleep(pool.locked().timeout.unwrap()).await;
+
+        let mut checkout = pool.checkout(key.clone());
+        let poll_once = PollOnce(&mut checkout);
+        // checkout.await should clean out the expired
+        poll_once.await;
+        assert!(pool.locked().idle.get(&key).is_none());
+    }
+
+    #[test]
+    fn test_pool_max_idle_per_host() {
+        let pool = pool_max_idle_no_timer(2);
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        // pooled and dropped 3, max_idle should only allow 2
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(2)
+        );
+    }
+
+    #[cfg(feature = "runtime")]
+    #[tokio::test]
+    async fn test_pool_timer_removes_expired() {
+        let _ = pretty_env_logger::try_init();
+        tokio::time::pause();
+
+        let pool = Pool::new(
+            super::Config {
+                idle_timeout: Some(Duration::from_millis(10)),
+                max_idle_per_host: std::usize::MAX,
+            },
+            &Exec::Default,
+        );
+
+        let key = host_key("foo");
+
+        pool.pooled(c(key.clone()), Uniq(41));
+        pool.pooled(c(key.clone()), Uniq(5));
+        pool.pooled(c(key.clone()), Uniq(99));
+
+        assert_eq!(
+            pool.locked().idle.get(&key).map(|entries| entries.len()),
+            Some(3)
+        );
+
+        // Let the timer tick passed the expiration...
+        tokio::time::advance(Duration::from_millis(30)).await;
+        // Yield so the Interval can reap...
+        tokio::task::yield_now().await;
+
+        assert!(pool.locked().idle.get(&key).is_none());
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_task_unparked() {
+        use futures_util::future::join;
+        use futures_util::FutureExt;
+
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        let pooled = pool.pooled(c(key.clone()), Uniq(41));
+
+        let checkout = join(pool.checkout(key), async {
+            // the checkout future will park first,
+            // and then this lazy future will be polled, which will insert
+            // the pooled back into the pool
+            //
+            // this test makes sure that doing so will unpark the checkout
+            drop(pooled);
+        })
+        .map(|(entry, _)| entry);
+
+        assert_eq!(*checkout.await.unwrap(), Uniq(41));
+    }
+
+    #[tokio::test]
+    async fn test_pool_checkout_drop_cleans_up_waiters() {
+        let pool = pool_no_timer::<Uniq<i32>>();
+        let key = host_key("foo");
+
+        let mut checkout1 = pool.checkout(key.clone());
+        let mut checkout2 = pool.checkout(key.clone());
+
+        let poll_once1 = PollOnce(&mut checkout1);
+        let poll_once2 = PollOnce(&mut checkout2);
+
+        // first poll needed to get into Pool's parked
+        poll_once1.await;
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 1);
+        poll_once2.await;
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 2);
+
+        // on drop, clean up Pool
+        drop(checkout1);
+        assert_eq!(pool.locked().waiters.get(&key).unwrap().len(), 1);
+
+        drop(checkout2);
+        assert!(pool.locked().waiters.get(&key).is_none());
+    }
+
+    #[derive(Debug)]
+    struct CanClose {
+        #[allow(unused)]
+        val: i32,
+        closed: bool,
+    }
+
+    impl Poolable for CanClose {
+        fn is_open(&self) -> bool {
+            !self.closed
+        }
+
+        fn reserve(self) -> Reservation<Self> {
+            Reservation::Unique(self)
+        }
+
+        fn can_share(&self) -> bool {
+            false
+        }
+    }
+
+    #[test]
+    fn pooled_drop_if_closed_doesnt_reinsert() {
+        let pool = pool_no_timer();
+        let key = host_key("foo");
+        pool.pooled(
+            c(key.clone()),
+            CanClose {
+                val: 57,
+                closed: true,
+            },
+        );
+
+        assert!(!pool.locked().idle.contains_key(&key));
+    }
+}