fix(pool): spawn task for before_acquire

Author: abonander

sqlx-core/src/pool/inner.rs

@@ -13,7 +13,9 @@ use std::task::ready;
 use crate::logger::private_level_filter_to_trace_level;
 use crate::pool::connect::{ConnectPermit, ConnectionCounter, DynConnector};
 use crate::pool::idle::IdleQueue;
-use crate::private_tracing_dynamic_event;
+use crate::rt::JoinHandle;
+use crate::{private_tracing_dynamic_event, rt};
+use either::Either;
 use futures_util::future::{self, OptionFuture};
 use futures_util::FutureExt;
 use std::time::{Duration, Instant};
@@ -116,7 +118,7 @@ impl<DB: Database> PoolInner<DB> {
         let mut close_event = pin!(self.close_event());
         let mut deadline = pin!(crate::rt::sleep(self.options.acquire_timeout));
         let mut acquire_idle = pin!(self.idle.acquire(self).fuse());
-        let mut check_idle = pin!(OptionFuture::from(None));
+        let mut before_acquire = OptionFuture::from(None);
         let mut acquire_connect_permit = pin!(OptionFuture::from(Some(
             self.counter.acquire_permit(self).fuse()
         )));
@@ -144,21 +146,26 @@ impl<DB: Database> PoolInner<DB> {
 
             // Attempt to acquire a connection from the idle queue.
             if let Ready(idle) = acquire_idle.poll_unpin(cx) {
-                check_idle.set(Some(check_idle_conn(idle, &self.options)).into());
+                // If we acquired an idle connection, run any checks that need to be done.
+                //
+                // Includes `test_on_acquire` and the `before_acquire` callback, if set.
+                match finish_acquire(idle) {
+                    // There are checks needed to be done, so they're spawned as a task
+                    // to be cancellation-safe.
+                    Either::Left(check_task) => {
+                        before_acquire = Some(check_task).into();
+                    }
+                    // The connection is ready to go.
+                    Either::Right(conn) => {
+                        return Ready(Ok(conn));
+                    }
+                }
             }
 
-            // If we acquired an idle connection, run any checks that need to be done.
-            //
-            // Includes `test_on_acquire` and the `before_acquire` callback, if set.
-            //
-            // We don't want to race this step if it's already running because canceling it
-            // will result in the potentially unnecessary closure of a connection.
-            //
-            // Instead, we just wait and see what happens. If we already started connecting,
-            // that'll happen concurrently.
-            match ready!(check_idle.poll_unpin(cx)) {
+            // Poll the task returned by `finish_acquire`
+            match ready!(before_acquire.poll_unpin(cx)) {
                 // The `.reattach()` call errors with "type annotations needed" if not qualified.
-                Some(Ok(live)) => return Ready(Ok(Floating::reattach(live))),
+                Some(Ok(conn)) => return Ready(Ok(conn)),
                 Some(Err(permit)) => {
                     // We don't strictly need to poll `connect` here; all we really want to do
                     // is to check if it is `None`. But since currently there's no getter for that,
@@ -178,7 +185,7 @@ impl<DB: Database> PoolInner<DB> {
                     // Attempt to acquire another idle connection concurrently to opening a new one.
                     acquire_idle.set(self.idle.acquire(self).fuse());
                     // Annoyingly, `OptionFuture` doesn't fuse to `None` on its own
-                    check_idle.set(None.into());
+                    before_acquire = None.into();
                 }
                 None => (),
             }
@@ -289,42 +296,51 @@ fn is_beyond_idle_timeout<DB: Database>(idle: &Idle<DB>, options: &PoolOptions<D
         .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>>, ConnectPermit<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`");
+/// Execute `test_before_acquire` and/or `before_acquire` in a background task, if applicable.
+/// 
+/// Otherwise, immediately returns the connection.
+fn finish_acquire<DB: Database>(
+    mut conn: Floating<DB, Idle<DB>>
+) -> Either<JoinHandle<Result<PoolConnection<DB>, ConnectPermit<DB>>>, PoolConnection<DB>> {
+    let pool = conn.permit.pool();
+    
+    if pool.options.test_before_acquire || pool.options.before_acquire.is_some() {
+        // Spawn a task so the call may complete even if `acquire()` is cancelled.
+        return Either::Left(rt::spawn(async move {
+            // 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);
             }
 
-            Ok(true) => {}
-        }
-    }
+            if let Some(test) = &conn.permit.pool().options.before_acquire {
+                let meta = conn.metadata();
+                match test(&mut conn.inner.live.raw, meta).await {
+                    Ok(false) => {
+                        // connection was rejected by user-defined hook, close nicely
+                        return Err(conn.close().await);
+                    }
 
-    // No need to re-connect; connection is alive or we don't care
-    Ok(conn.into_live())
+                    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) => {}
+                }
+            }
+            
+            Ok(conn.into_live().reattach())
+        }));
+    }
+    
+    // No checks are configured, return immediately.
+    Either::Right(conn.into_live().reattach())
 }
 
 fn spawn_maintenance_tasks<DB: Database>(pool: &Arc<PoolInner<DB>>) {
@@ -353,7 +369,7 @@ fn spawn_maintenance_tasks<DB: Database>(pool: &Arc<PoolInner<DB>>) {
     // Immediately cancel this task if the pool is closed.
     let mut close_event = pool.close_event();
 
-    crate::rt::spawn(async move {
+    rt::spawn(async move {
         let _ = close_event
             .do_until(async {
                 // If the last handle to the pool was dropped while we were sleeping
@@ -386,10 +402,10 @@ fn spawn_maintenance_tasks<DB: Database>(pool: &Arc<PoolInner<DB>>) {
 
                     if let Some(duration) = next_run.checked_duration_since(Instant::now()) {
                         // `async-std` doesn't have a `sleep_until()`
-                        crate::rt::sleep(duration).await;
+                        rt::sleep(duration).await;
                     } else {
                         // `next_run` is in the past, just yield.
-                        crate::rt::yield_now().await;
+                        rt::yield_now().await;
                     }
                 }
             })