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fix(postgres): make advisory lock cancel safe #4199

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fix(postgres): make advisory lock cancel safe #4199

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fix(postgres): make advisory lock cancel safe
joeydewaal Mar 23, 2026
94894c5
fix(postgres): prepare advisory lock acquire query first
joeydewaal Mar 24, 2026
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34 changes: 20 additions & 14 deletions sqlx-postgres/src/advisory_lock.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@ use crate::Either;
use crate::PgConnection;
use hkdf::Hkdf;
use sha2::Sha256;
use sqlx_core::executor::Executor;
use sqlx_core::sql_str::SqlSafeStr;
use std::ops::{Deref, DerefMut};
use std::sync::Arc;
use std::sync::OnceLock;
Expand Down Expand Up @@ -203,23 +205,27 @@ impl PgAdvisoryLock {
&self,
mut conn: C,
) -> Result<PgAdvisoryLockGuard<C>> {
let query = match &self.key {
PgAdvisoryLockKey::BigInt(_) => "SELECT pg_advisory_lock($1)",
PgAdvisoryLockKey::IntPair(_, _) => "SELECT pg_advisory_lock($1, $2)",
};

let stmt = conn.as_mut().prepare(query.into_sql_str()).await?;
let query = crate::query::query_statement(&stmt);

// We're wrapping the connection in a `PgAdvisoryLockGuard` early here on purpose. If this
// future is dropped, the lock will be released in the drop impl.
let mut guard = PgAdvisoryLockGuard::new(self.clone(), conn);
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@bonsairobo bonsairobo Mar 24, 2026

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Won't this also cause us to release the lock on drop before it's even been acquired? Is that OK?

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@bonsairobo bonsairobo Mar 24, 2026

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Ah nvm, I assume anything done before the first await happens atomically.

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@bonsairobo bonsairobo Mar 24, 2026

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Actually, is it possible that the first await yields before actually managing to send the lock query? Like maybe if the TCP send buffer is full?

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@joeydewaal joeydewaal Mar 24, 2026

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Yeah the future can be dropped before it's actually sent out. But then it's in the write buffer, which is flushed the next time before the connection is used.

I guess the worst case would be when the query isn't prepared. Then the drop is going to queue an unnecessary release. Thanks for calling this out.

let conn = guard.conn.as_mut().unwrap();

match &self.key {
PgAdvisoryLockKey::BigInt(key) => {
crate::query::query("SELECT pg_advisory_lock($1)")
.bind(key)
.execute(conn.as_mut())
.await?;
}
PgAdvisoryLockKey::IntPair(key1, key2) => {
crate::query::query("SELECT pg_advisory_lock($1, $2)")
.bind(key1)
.bind(key2)
.execute(conn.as_mut())
.await?;
}
PgAdvisoryLockKey::BigInt(key) => query.bind(key),
PgAdvisoryLockKey::IntPair(key1, key2) => query.bind(key1).bind(key2),
}
.execute(conn.as_mut())
.await?;

Ok(PgAdvisoryLockGuard::new(self.clone(), conn))
Ok(guard)
}

/// Acquires an exclusive lock using `pg_try_advisory_lock()`, returning immediately
Expand Down
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