sqlx_core/pool/inner.rs
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use super::connection::{Floating, Idle, Live};
use crate::connection::ConnectOptions;
use crate::connection::Connection;
use crate::database::Database;
use crate::error::Error;
use crate::pool::{deadline_as_timeout, CloseEvent, Pool, PoolOptions};
use crossbeam_queue::ArrayQueue;
use crate::sync::{AsyncSemaphore, AsyncSemaphoreReleaser};
use std::cmp;
use std::future::Future;
use std::sync::atomic::{AtomicBool, AtomicU32, AtomicUsize, Ordering};
use std::sync::{Arc, RwLock};
use std::task::Poll;
use crate::logger::private_level_filter_to_trace_level;
use crate::pool::options::PoolConnectionMetadata;
use crate::private_tracing_dynamic_event;
use futures_util::future::{self};
use futures_util::FutureExt;
use std::time::{Duration, Instant};
use tracing::Level;
pub(crate) struct PoolInner<DB: Database> {
pub(super) connect_options: RwLock<Arc<<DB::Connection as Connection>::Options>>,
pub(super) idle_conns: ArrayQueue<Idle<DB>>,
pub(super) semaphore: AsyncSemaphore,
pub(super) size: AtomicU32,
pub(super) num_idle: AtomicUsize,
is_closed: AtomicBool,
pub(super) on_closed: event_listener::Event,
pub(super) options: PoolOptions<DB>,
pub(crate) acquire_time_level: Option<Level>,
pub(crate) acquire_slow_level: Option<Level>,
}
impl<DB: Database> PoolInner<DB> {
pub(super) fn new_arc(
options: PoolOptions<DB>,
connect_options: <DB::Connection as Connection>::Options,
) -> Arc<Self> {
let capacity = options.max_connections as usize;
let semaphore_capacity = if let Some(parent) = &options.parent_pool {
assert!(options.max_connections <= parent.options().max_connections);
assert_eq!(options.fair, parent.options().fair);
// The child pool must steal permits from the parent
0
} else {
capacity
};
let pool = Self {
connect_options: RwLock::new(Arc::new(connect_options)),
idle_conns: ArrayQueue::new(capacity),
semaphore: AsyncSemaphore::new(options.fair, semaphore_capacity),
size: AtomicU32::new(0),
num_idle: AtomicUsize::new(0),
is_closed: AtomicBool::new(false),
on_closed: event_listener::Event::new(),
acquire_time_level: private_level_filter_to_trace_level(options.acquire_time_level),
acquire_slow_level: private_level_filter_to_trace_level(options.acquire_slow_level),
options,
};
let pool = Arc::new(pool);
spawn_maintenance_tasks(&pool);
pool
}
pub(super) fn size(&self) -> u32 {
self.size.load(Ordering::Acquire)
}
pub(super) fn num_idle(&self) -> usize {
// We don't use `self.idle_conns.len()` as it waits for the internal
// head and tail pointers to stop changing for a moment before calculating the length,
// which may take a long time at high levels of churn.
//
// By maintaining our own atomic count, we avoid that issue entirely.
self.num_idle.load(Ordering::Acquire)
}
pub(super) fn is_closed(&self) -> bool {
self.is_closed.load(Ordering::Acquire)
}
fn mark_closed(&self) {
self.is_closed.store(true, Ordering::Release);
self.on_closed.notify(usize::MAX);
}
pub(super) fn close<'a>(self: &'a Arc<Self>) -> impl Future<Output = ()> + 'a {
self.mark_closed();
async move {
for permits in 1..=self.options.max_connections {
// Close any currently idle connections in the pool.
while let Some(idle) = self.idle_conns.pop() {
let _ = idle.live.float((*self).clone()).close().await;
}
if self.size() == 0 {
break;
}
// Wait for all permits to be released.
let _permits = self.semaphore.acquire(permits).await;
}
}
}
pub(crate) fn close_event(&self) -> CloseEvent {
CloseEvent {
listener: (!self.is_closed()).then(|| self.on_closed.listen()),
}
}
/// Attempt to pull a permit from `self.semaphore` or steal one from the parent.
///
/// If we steal a permit from the parent but *don't* open a connection,
/// it should be returned to the parent.
async fn acquire_permit<'a>(self: &'a Arc<Self>) -> Result<AsyncSemaphoreReleaser<'a>, Error> {
let parent = self
.parent()
// If we're already at the max size, we shouldn't try to steal from the parent.
// This is just going to cause unnecessary churn in `acquire()`.
.filter(|_| self.size() < self.options.max_connections);
let acquire_self = self.semaphore.acquire(1).fuse();
let mut close_event = self.close_event();
if let Some(parent) = parent {
let acquire_parent = parent.0.semaphore.acquire(1);
let parent_close_event = parent.0.close_event();
futures_util::pin_mut!(
acquire_parent,
acquire_self,
close_event,
parent_close_event
);
let mut poll_parent = false;
future::poll_fn(|cx| {
if close_event.as_mut().poll(cx).is_ready() {
return Poll::Ready(Err(Error::PoolClosed));
}
if parent_close_event.as_mut().poll(cx).is_ready() {
// Propagate the parent's close event to the child.
self.mark_closed();
return Poll::Ready(Err(Error::PoolClosed));
}
if let Poll::Ready(permit) = acquire_self.as_mut().poll(cx) {
return Poll::Ready(Ok(permit));
}
// Don't try the parent right away.
if poll_parent {
acquire_parent.as_mut().poll(cx).map(Ok)
} else {
poll_parent = true;
cx.waker().wake_by_ref();
Poll::Pending
}
})
.await
} else {
close_event.do_until(acquire_self).await
}
}
fn parent(&self) -> Option<&Pool<DB>> {
self.options.parent_pool.as_ref()
}
#[inline]
pub(super) fn try_acquire(self: &Arc<Self>) -> Option<Floating<DB, Idle<DB>>> {
if self.is_closed() {
return None;
}
let permit = self.semaphore.try_acquire(1)?;
self.pop_idle(permit).ok()
}
fn pop_idle<'a>(
self: &'a Arc<Self>,
permit: AsyncSemaphoreReleaser<'a>,
) -> Result<Floating<DB, Idle<DB>>, AsyncSemaphoreReleaser<'a>> {
if let Some(idle) = self.idle_conns.pop() {
self.num_idle.fetch_sub(1, Ordering::AcqRel);
Ok(Floating::from_idle(idle, (*self).clone(), permit))
} else {
Err(permit)
}
}
pub(super) fn release(&self, floating: Floating<DB, Live<DB>>) {
// `options.after_release` and other checks are in `PoolConnection::return_to_pool()`.
let Floating { inner: idle, guard } = floating.into_idle();
if self.idle_conns.push(idle).is_err() {
panic!("BUG: connection queue overflow in release()");
}
// NOTE: we need to make sure we drop the permit *after* we push to the idle queue
// don't decrease the size
guard.release_permit();
self.num_idle.fetch_add(1, Ordering::AcqRel);
}
/// Try to atomically increment the pool size for a new connection.
///
/// Returns `Err` if the pool is at max capacity already or is closed.
pub(super) fn try_increment_size<'a>(
self: &'a Arc<Self>,
permit: AsyncSemaphoreReleaser<'a>,
) -> Result<DecrementSizeGuard<DB>, AsyncSemaphoreReleaser<'a>> {
let result = self
.size
.fetch_update(Ordering::AcqRel, Ordering::Acquire, |size| {
if self.is_closed() {
return None;
}
size.checked_add(1)
.filter(|size| size <= &self.options.max_connections)
});
match result {
// we successfully incremented the size
Ok(_) => Ok(DecrementSizeGuard::from_permit((*self).clone(), permit)),
// the pool is at max capacity or is closed
Err(_) => Err(permit),
}
}
pub(super) async fn acquire(self: &Arc<Self>) -> Result<Floating<DB, Live<DB>>, Error> {
if self.is_closed() {
return Err(Error::PoolClosed);
}
let acquire_started_at = Instant::now();
let deadline = acquire_started_at + self.options.acquire_timeout;
let acquired = crate::rt::timeout(
self.options.acquire_timeout,
async {
loop {
// Handles the close-event internally
let permit = self.acquire_permit().await?;
// First attempt to pop a connection from the idle queue.
let guard = match self.pop_idle(permit) {
// Then, check that we can use it...
Ok(conn) => match check_idle_conn(conn, &self.options).await {
// All good!
Ok(live) => return Ok(live),
// if the connection isn't usable for one reason or another,
// we get the `DecrementSizeGuard` back to open a new one
Err(guard) => guard,
},
Err(permit) => if let Ok(guard) = self.try_increment_size(permit) {
// we can open a new connection
guard
} else {
// This can happen for a child pool that's at its connection limit,
// or if the pool was closed between `acquire_permit()` and
// `try_increment_size()`.
tracing::debug!("woke but was unable to acquire idle connection or open new one; retrying");
// If so, we're likely in the current-thread runtime if it's Tokio,
// and so we should yield to let any spawned return_to_pool() tasks
// execute.
crate::rt::yield_now().await;
continue;
}
};
// Attempt to connect...
return self.connect(deadline, guard).await;
}
}
)
.await
.map_err(|_| Error::PoolTimedOut)??;
let acquired_after = acquire_started_at.elapsed();
let acquire_slow_level = self
.acquire_slow_level
.filter(|_| acquired_after > self.options.acquire_slow_threshold);
if let Some(level) = acquire_slow_level {
private_tracing_dynamic_event!(
target: "sqlx::pool::acquire",
level,
aquired_after_secs = acquired_after.as_secs_f64(),
slow_acquire_threshold_secs = self.options.acquire_slow_threshold.as_secs_f64(),
"acquired connection, but time to acquire exceeded slow threshold"
);
} else if let Some(level) = self.acquire_time_level {
private_tracing_dynamic_event!(
target: "sqlx::pool::acquire",
level,
aquired_after_secs = acquired_after.as_secs_f64(),
"acquired connection"
);
}
Ok(acquired)
}
pub(super) async fn connect(
self: &Arc<Self>,
deadline: Instant,
guard: DecrementSizeGuard<DB>,
) -> Result<Floating<DB, Live<DB>>, Error> {
if self.is_closed() {
return Err(Error::PoolClosed);
}
let mut backoff = Duration::from_millis(10);
let max_backoff = deadline_as_timeout(deadline)? / 5;
loop {
let timeout = deadline_as_timeout(deadline)?;
// clone the connect options arc so it can be used without holding the RwLockReadGuard
// across an async await point
let connect_options = self
.connect_options
.read()
.expect("write-lock holder panicked")
.clone();
// result here is `Result<Result<C, Error>, TimeoutError>`
// if this block does not return, sleep for the backoff timeout and try again
match crate::rt::timeout(timeout, connect_options.connect()).await {
// successfully established connection
Ok(Ok(mut raw)) => {
// See comment on `PoolOptions::after_connect`
let meta = PoolConnectionMetadata {
age: Duration::ZERO,
idle_for: Duration::ZERO,
};
let res = if let Some(callback) = &self.options.after_connect {
callback(&mut raw, meta).await
} else {
Ok(())
};
match res {
Ok(()) => return Ok(Floating::new_live(raw, guard)),
Err(error) => {
tracing::error!(%error, "error returned from after_connect");
// The connection is broken, don't try to close nicely.
let _ = raw.close_hard().await;
// Fall through to the backoff.
}
}
}
// an IO error while connecting is assumed to be the system starting up
Ok(Err(Error::Io(e))) if e.kind() == std::io::ErrorKind::ConnectionRefused => (),
// We got a transient database error, retry.
Ok(Err(Error::Database(error))) if error.is_transient_in_connect_phase() => (),
// Any other error while connection should immediately
// terminate and bubble the error up
Ok(Err(e)) => return Err(e),
// timed out
Err(_) => return Err(Error::PoolTimedOut),
}
// If the connection is refused, wait in exponentially
// increasing steps for the server to come up,
// capped by a factor of the remaining time until the deadline
crate::rt::sleep(backoff).await;
backoff = cmp::min(backoff * 2, max_backoff);
}
}
/// Try to maintain `min_connections`, returning any errors (including `PoolTimedOut`).
pub async fn try_min_connections(self: &Arc<Self>, deadline: Instant) -> Result<(), Error> {
while self.size() < self.options.min_connections {
// Don't wait for a semaphore permit.
//
// If no extra permits are available then we shouldn't be trying to spin up
// connections anyway.
let Some(permit) = self.semaphore.try_acquire(1) else {
return Ok(());
};
// We must always obey `max_connections`.
let Some(guard) = self.try_increment_size(permit).ok() else {
return Ok(());
};
// We skip `after_release` since the connection was never provided to user code
// besides `after_connect`, if they set it.
self.release(self.connect(deadline, guard).await?);
}
Ok(())
}
/// Attempt to maintain `min_connections`, logging if unable.
pub async fn min_connections_maintenance(self: &Arc<Self>, deadline: Option<Instant>) {
let deadline = deadline.unwrap_or_else(|| {
// Arbitrary default deadline if the caller doesn't care.
Instant::now() + Duration::from_secs(300)
});
match self.try_min_connections(deadline).await {
Ok(()) => (),
Err(Error::PoolClosed) => (),
Err(Error::PoolTimedOut) => {
tracing::debug!("unable to complete `min_connections` maintenance before deadline")
}
Err(error) => tracing::debug!(%error, "error while maintaining min_connections"),
}
}
}
impl<DB: Database> Drop for PoolInner<DB> {
fn drop(&mut self) {
self.mark_closed();
if let Some(parent) = &self.options.parent_pool {
// Release the stolen permits.
parent.0.semaphore.release(self.semaphore.permits());
}
}
}
/// Returns `true` if the connection has exceeded `options.max_lifetime` if set, `false` otherwise.
pub(super) fn is_beyond_max_lifetime<DB: Database>(
live: &Live<DB>,
options: &PoolOptions<DB>,
) -> bool {
options
.max_lifetime
.map_or(false, |max| live.created_at.elapsed() > max)
}
/// Returns `true` if the connection has exceeded `options.idle_timeout` if set, `false` otherwise.
fn is_beyond_idle_timeout<DB: Database>(idle: &Idle<DB>, options: &PoolOptions<DB>) -> bool {
options
.idle_timeout
.map_or(false, |timeout| idle.idle_since.elapsed() > timeout)
}
async fn check_idle_conn<DB: Database>(
mut conn: Floating<DB, Idle<DB>>,
options: &PoolOptions<DB>,
) -> Result<Floating<DB, Live<DB>>, DecrementSizeGuard<DB>> {
if options.test_before_acquire {
// Check that the connection is still live
if let Err(error) = conn.ping().await {
// an error here means the other end has hung up or we lost connectivity
// either way we're fine to just discard the connection
// the error itself here isn't necessarily unexpected so WARN is too strong
tracing::info!(%error, "ping on idle connection returned error");
// connection is broken so don't try to close nicely
return Err(conn.close_hard().await);
}
}
if let Some(test) = &options.before_acquire {
let meta = conn.metadata();
match test(&mut conn.live.raw, meta).await {
Ok(false) => {
// connection was rejected by user-defined hook, close nicely
return Err(conn.close().await);
}
Err(error) => {
tracing::warn!(%error, "error from `before_acquire`");
// connection is broken so don't try to close nicely
return Err(conn.close_hard().await);
}
Ok(true) => {}
}
}
// No need to re-connect; connection is alive or we don't care
Ok(conn.into_live())
}
fn spawn_maintenance_tasks<DB: Database>(pool: &Arc<PoolInner<DB>>) {
// NOTE: use `pool_weak` for the maintenance tasks
// so they don't keep `PoolInner` from being dropped.
let pool_weak = Arc::downgrade(pool);
let period = match (pool.options.max_lifetime, pool.options.idle_timeout) {
(Some(it), None) | (None, Some(it)) => it,
(Some(a), Some(b)) => cmp::min(a, b),
(None, None) => {
if pool.options.min_connections > 0 {
crate::rt::spawn(async move {
if let Some(pool) = pool_weak.upgrade() {
pool.min_connections_maintenance(None).await;
}
});
}
return;
}
};
// Immediately cancel this task if the pool is closed.
let mut close_event = pool.close_event();
crate::rt::spawn(async move {
let _ = close_event
.do_until(async {
// If the last handle to the pool was dropped while we were sleeping
while let Some(pool) = pool_weak.upgrade() {
if pool.is_closed() {
return;
}
let next_run = Instant::now() + period;
// Go over all idle connections, check for idleness and lifetime,
// and if we have fewer than min_connections after reaping a connection,
// open a new one immediately. Note that other connections may be popped from
// the queue in the meantime - that's fine, there is no harm in checking more
for _ in 0..pool.num_idle() {
if let Some(conn) = pool.try_acquire() {
if is_beyond_idle_timeout(&conn, &pool.options)
|| is_beyond_max_lifetime(&conn, &pool.options)
{
let _ = conn.close().await;
pool.min_connections_maintenance(Some(next_run)).await;
} else {
pool.release(conn.into_live());
}
}
}
// Don't hold a reference to the pool while sleeping.
drop(pool);
if let Some(duration) = next_run.checked_duration_since(Instant::now()) {
// `async-std` doesn't have a `sleep_until()`
crate::rt::sleep(duration).await;
} else {
// `next_run` is in the past, just yield.
crate::rt::yield_now().await;
}
}
})
.await;
});
}
/// RAII guard returned by `Pool::try_increment_size()` and others.
///
/// Will decrement the pool size if dropped, to avoid semantically "leaking" connections
/// (where the pool thinks it has more connections than it does).
pub(in crate::pool) struct DecrementSizeGuard<DB: Database> {
pub(crate) pool: Arc<PoolInner<DB>>,
cancelled: bool,
}
impl<DB: Database> DecrementSizeGuard<DB> {
/// Create a new guard that will release a semaphore permit on-drop.
pub fn new_permit(pool: Arc<PoolInner<DB>>) -> Self {
Self {
pool,
cancelled: false,
}
}
pub fn from_permit(pool: Arc<PoolInner<DB>>, permit: AsyncSemaphoreReleaser<'_>) -> Self {
// here we effectively take ownership of the permit
permit.disarm();
Self::new_permit(pool)
}
/// Release the semaphore permit without decreasing the pool size.
///
/// If the permit was stolen from the pool's parent, it will be returned to the child's semaphore.
fn release_permit(self) {
self.pool.semaphore.release(1);
self.cancel();
}
pub fn cancel(mut self) {
self.cancelled = true;
}
}
impl<DB: Database> Drop for DecrementSizeGuard<DB> {
fn drop(&mut self) {
if !self.cancelled {
self.pool.size.fetch_sub(1, Ordering::AcqRel);
// and here we release the permit we got on construction
self.pool.semaphore.release(1);
}
}
}