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// Copyright (c) 2019 mysql_async contributors
//
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. All files in the project carrying such notice may not be copied,
// modified, or distributed except according to those terms.
use futures_core::stream::Stream;
use futures_util::{stream::futures_unordered::FuturesUnordered, FutureExt};
use tokio::sync::mpsc;
use std::{
future::Future,
pin::Pin,
sync::{atomic::Ordering, Arc},
task::{Context, Poll},
};
use super::{IdlingConn, Inner};
use crate::{queryable::transaction::TxStatus, BoxFuture, Conn, PoolOpts};
use tokio::sync::mpsc::UnboundedReceiver;
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub(crate) struct Recycler {
inner: Arc<Inner>,
discard: FuturesUnordered<BoxFuture<'static, ()>>,
discarded: usize,
cleaning: FuturesUnordered<BoxFuture<'static, Conn>>,
reset: FuturesUnordered<BoxFuture<'static, Conn>>,
// Option<Conn> so that we have a way to send a "I didn't make a Conn after all" signal
dropped: mpsc::UnboundedReceiver<Option<Conn>>,
/// Pool options.
pool_opts: PoolOpts,
eof: bool,
}
impl Recycler {
pub fn new(
pool_opts: PoolOpts,
inner: Arc<Inner>,
dropped: UnboundedReceiver<Option<Conn>>,
) -> Self {
Self {
inner,
discard: FuturesUnordered::new(),
discarded: 0,
cleaning: FuturesUnordered::new(),
reset: FuturesUnordered::new(),
dropped,
pool_opts,
eof: false,
}
}
}
impl Future for Recycler {
type Output = ();
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 {
// drop unestablished connection
$self
.inner
.metrics
.discarded_unestablished_connection
.fetch_add(1, Ordering::Relaxed);
$self.discard.push(futures_util::future::ok(()).boxed());
} else if $conn.inner.tx_status != TxStatus::None || $conn.has_pending_result() {
$self
.inner
.metrics
.dirty_connection_return
.fetch_add(1, Ordering::Relaxed);
$self.cleaning.push($conn.cleanup_for_pool().boxed());
} else if $conn.expired() || close {
$self
.inner
.metrics
.discarded_expired_connection
.fetch_add(1, Ordering::Relaxed);
$self.discard.push($conn.close_conn().boxed());
} else if $conn.inner.reset_upon_returning_to_a_pool {
$self
.inner
.metrics
.resetting_connection
.fetch_add(1, Ordering::Relaxed);
$self.reset.push($conn.reset_for_pool().boxed());
} else {
conn_return!($self, $conn, false);
}
};
}
while !self.eof {
// see if there are more connections for us to recycle
match Pin::new(&mut self.dropped).poll_recv(cx) {
Poll::Ready(Some(Some(conn))) => {
assert!(conn.inner.pool.is_none());
conn_decision!(self, conn);
}
Poll::Ready(Some(None)) => {
// someone signaled us that it's exit time
close = self.inner.close.load(Ordering::Acquire);
assert!(close);
continue;
}
Poll::Ready(None) => {
// no more connections are coming -- time to exit!
self.inner.close.store(true, Ordering::Release);
self.eof = true;
close = true;
}
Poll::Pending => {
// nope -- but let's still make progress on the ones we have
break;
}
}
}
// 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()
{
assert!(conn.inner.pool.is_none());
conn_decision!(self, conn);
}
}
// are any dirty connections ready for us to reclaim?
loop {
match Pin::new(&mut self.cleaning).poll_next(cx) {
Poll::Pending | Poll::Ready(None) => break,
Poll::Ready(Some(Ok(conn))) => conn_decision!(self, conn),
Poll::Ready(Some(Err(e))) => {
// an error occurred while cleaning a connection.
// what do we do? replace it with a new connection?
// for a conn to end up in cleaning, it must have come through .dropped.
// anything that comes through .dropped we know has .pool.is_none().
// therefore, dropping the conn won't decrement .exist, so we need to do that.
self.discarded += 1;
self.inner
.metrics
.discarded_error_during_cleanup
.fetch_add(1, Ordering::Relaxed);
// NOTE: we're discarding the error here
let _ = e;
}
}
}
// let's iterate through connections being successfully reset
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(Err(e))) => {
// an error during reset.
// replace with a new connection
self.discarded += 1;
self.inner
.metrics
.discarded_error_during_cleanup
.fetch_add(1, Ordering::Relaxed);
// NOTE: we're discarding the error here
let _ = e;
}
}
}
// are there any torn-down connections for us to deal with?
loop {
match Pin::new(&mut self.discard).poll_next(cx) {
Poll::Pending | Poll::Ready(None) => break,
Poll::Ready(Some(Ok(()))) => {
// yes! count it.
// note that we must decrement .exist since the connection does not have a
// .pool, and therefore won't do anything useful when it is dropped.
self.discarded += 1
}
Poll::Ready(Some(Err(e))) => {
// an error occurred while closing a connection.
// what do we do? we still replace it with a new connection..
self.discarded += 1;
self.inner
.metrics
.discarded_error_during_cleanup
.fetch_add(1, Ordering::Relaxed);
// NOTE: we're discarding the error here
let _ = e;
}
}
}
if self.discarded != 0 {
// we need to open up slots for new connctions to be established!
let mut exchange = self.inner.exchange.lock().unwrap();
exchange.exist -= self.discarded;
self.inner
.metrics
.connection_count
.store(exchange.exist, Ordering::Relaxed);
for _ in 0..self.discarded {
if let Some(w) = exchange.waiting.pop() {
w.wake();
}
}
drop(exchange);
self.discarded = 0;
}
// NOTE: we are asserting here that no more connections will ever be returned to
// us. see the explanation in Pool::poll_new_conn for why this is okay, even during
// races on .exist
let effectively_eof = close && self.inner.exchange.lock().unwrap().exist == 0;
if (self.eof || effectively_eof)
&& self.cleaning.is_empty()
&& self.discard.is_empty()
&& self.reset.is_empty()
{
// we know that all Pool handles have been dropped (self.dropped.poll returned None).
// if this assertion fails, where are the remaining connections?
assert_eq!(self.inner.exchange.lock().unwrap().available.len(), 0);
// NOTE: it is _necessary_ that we set this _before_ we call .wake
// otherwise, the following may happen to the DisconnectPool future:
//
// - We wake all in .wake
// - DisconnectPool::poll adds to .wake
// - DisconnectPool::poll reads .closed == false
// - We set .closed = true
//
// At this point, DisconnectPool::poll will never be notified again.
self.inner.closed.store(true, Ordering::Release);
}
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();
}
// we're about to exit, so there better be no outstanding connections
assert_eq!(exchange.exist, 0);
assert_eq!(exchange.available.len(), 0);
drop(exchange);
Poll::Ready(())
} else {
Poll::Pending
}
}
}
impl Drop for Recycler {
fn drop(&mut self) {
if !self.inner.closed.load(Ordering::Acquire) {
// user did not wait for outstanding connections to finish!
// this is not good -- we won't be able to shut down our connections cleanly
// all we can do is try to ensure a clean shutdown
self.inner.close.store(true, Ordering::SeqCst);
}
}
}