feat(postgres): remove lifetime from PgAdvisoryLockGuard

Unlike with CPU synchronization primitives, there is no semantic requirement
that the guard borrows the lock object.

We preserve the optimization of memoizing the release query by wrapping it in
an Arc. This way all instances of `PgAdvisoryLockGuard` that originate from the
same lock will share a single instance of the release query.

sqlx-postgres/src/advisory_lock.rs

@@ -5,6 +5,7 @@ use hkdf::Hkdf;
 use once_cell::sync::OnceCell;
 use sha2::Sha256;
 use std::ops::{Deref, DerefMut};
+use std::sync::Arc;
 
 /// A mutex-like type utilizing [Postgres advisory locks].
 ///
@@ -37,7 +38,7 @@ use std::ops::{Deref, DerefMut};
 pub struct PgAdvisoryLock {
     key: PgAdvisoryLockKey,
     /// The query to execute to release this lock.
-    release_query: OnceCell<String>,
+    release_query: Arc<OnceCell<String>>,
 }
 
 /// A key type natively used by Postgres advisory locks.
@@ -77,8 +78,8 @@ pub enum PgAdvisoryLockKey {
 ///
 /// This means the lock is not actually released as soon as the guard is dropped. To ensure the
 /// lock is eagerly released, you can call [`.release_now().await`][Self::release_now()].
-pub struct PgAdvisoryLockGuard<'lock, C: AsMut<PgConnection>> {
-    lock: &'lock PgAdvisoryLock,
+pub struct PgAdvisoryLockGuard<C: AsMut<PgConnection>> {
+    lock: PgAdvisoryLock,
     conn: Option<C>,
 }
 
@@ -163,7 +164,7 @@ impl PgAdvisoryLock {
     pub fn with_key(key: PgAdvisoryLockKey) -> Self {
         Self {
             key,
-            release_query: OnceCell::new(),
+            release_query: Arc::new(OnceCell::new()),
         }
     }
 
@@ -201,7 +202,7 @@ impl PgAdvisoryLock {
     pub async fn acquire<C: AsMut<PgConnection>>(
         &self,
         mut conn: C,
-    ) -> Result<PgAdvisoryLockGuard<'_, C>> {
+    ) -> Result<PgAdvisoryLockGuard<C>> {
         match &self.key {
             PgAdvisoryLockKey::BigInt(key) => {
                 crate::query::query("SELECT pg_advisory_lock($1)")
@@ -218,7 +219,7 @@ impl PgAdvisoryLock {
             }
         }
 
-        Ok(PgAdvisoryLockGuard::new(self, conn))
+        Ok(PgAdvisoryLockGuard::new(self.clone(), conn))
     }
 
     /// Acquires an exclusive lock using `pg_try_advisory_lock()`, returning immediately
@@ -244,7 +245,7 @@ impl PgAdvisoryLock {
     pub async fn try_acquire<C: AsMut<PgConnection>>(
         &self,
         mut conn: C,
-    ) -> Result<Either<PgAdvisoryLockGuard<'_, C>, C>> {
+    ) -> Result<Either<PgAdvisoryLockGuard<C>, C>> {
         let locked: bool = match &self.key {
             PgAdvisoryLockKey::BigInt(key) => {
                 crate::query_scalar::query_scalar("SELECT pg_try_advisory_lock($1)")
@@ -262,7 +263,7 @@ impl PgAdvisoryLock {
         };
 
         if locked {
-            Ok(Either::Left(PgAdvisoryLockGuard::new(self, conn)))
+            Ok(Either::Left(PgAdvisoryLockGuard::new(self.clone(), conn)))
         } else {
             Ok(Either::Right(conn))
         }
@@ -322,8 +323,8 @@ impl PgAdvisoryLockKey {
 
 const NONE_ERR: &str = "BUG: PgAdvisoryLockGuard.conn taken";
 
-impl<'lock, C: AsMut<PgConnection>> PgAdvisoryLockGuard<'lock, C> {
-    fn new(lock: &'lock PgAdvisoryLock, conn: C) -> Self {
+impl<C: AsMut<PgConnection>> PgAdvisoryLockGuard<C> {
+    fn new(lock: PgAdvisoryLock, conn: C) -> Self {
         PgAdvisoryLockGuard {
             lock,
             conn: Some(conn),
@@ -362,7 +363,7 @@ impl<'lock, C: AsMut<PgConnection>> PgAdvisoryLockGuard<'lock, C> {
     }
 }
 
-impl<'lock, C: AsMut<PgConnection> + AsRef<PgConnection>> Deref for PgAdvisoryLockGuard<'lock, C> {
+impl<C: AsMut<PgConnection> + AsRef<PgConnection>> Deref for PgAdvisoryLockGuard<C> {
     type Target = PgConnection;
 
     fn deref(&self) -> &Self::Target {
@@ -376,17 +377,13 @@ impl<'lock, C: AsMut<PgConnection> + AsRef<PgConnection>> Deref for PgAdvisoryLo
 /// However, replacing the connection with a different one using, e.g. [`std::mem::replace()`]
 /// is a logic error and will cause a warning to be logged by the PostgreSQL server when this
 /// guard attempts to release the lock.
-impl<'lock, C: AsMut<PgConnection> + AsRef<PgConnection>> DerefMut
-    for PgAdvisoryLockGuard<'lock, C>
-{
+impl<C: AsMut<PgConnection> + AsRef<PgConnection>> DerefMut for PgAdvisoryLockGuard<C> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         self.conn.as_mut().expect(NONE_ERR).as_mut()
     }
 }
 
-impl<'lock, C: AsMut<PgConnection> + AsRef<PgConnection>> AsRef<PgConnection>
-    for PgAdvisoryLockGuard<'lock, C>
-{
+impl<C: AsMut<PgConnection> + AsRef<PgConnection>> AsRef<PgConnection> for PgAdvisoryLockGuard<C> {
     fn as_ref(&self) -> &PgConnection {
         self.conn.as_ref().expect(NONE_ERR).as_ref()
     }
@@ -398,7 +395,7 @@ impl<'lock, C: AsMut<PgConnection> + AsRef<PgConnection>> AsRef<PgConnection>
 /// However, replacing the connection with a different one using, e.g. [`std::mem::replace()`]
 /// is a logic error and will cause a warning to be logged by the PostgreSQL server when this
 /// guard attempts to release the lock.
-impl<'lock, C: AsMut<PgConnection>> AsMut<PgConnection> for PgAdvisoryLockGuard<'lock, C> {
+impl<C: AsMut<PgConnection>> AsMut<PgConnection> for PgAdvisoryLockGuard<C> {
     fn as_mut(&mut self) -> &mut PgConnection {
         self.conn.as_mut().expect(NONE_ERR).as_mut()
     }
@@ -407,7 +404,7 @@ impl<'lock, C: AsMut<PgConnection>> AsMut<PgConnection> for PgAdvisoryLockGuard<
 /// Queues a `pg_advisory_unlock()` call on the wrapped connection which will be flushed
 /// to the server the next time it is used, or when it is returned to [`PgPool`][crate::PgPool]
 /// in the case of [`PoolConnection<Postgres>`][crate::pool::PoolConnection].
-impl<'lock, C: AsMut<PgConnection>> Drop for PgAdvisoryLockGuard<'lock, C> {
+impl<C: AsMut<PgConnection>> Drop for PgAdvisoryLockGuard<C> {
     fn drop(&mut self) {
         if let Some(mut conn) = self.conn.take() {
             // Queue a simple query message to execute next time the connection is used.