sea-orm-sync + rusqlite , cannot put DatabaseConnection in OnceLock because it is not Sync

[johnny-smitherson]

Description

Can't put rusqlite database connection objects in statics / globals because of compiler error:

static DB_LOCK: std::sync::OnceLock<DatabaseConnection> = OnceLock::new();

This cause

error[E0277]: `(dyn for<'a, 'b> Fn(&'a sea_orm::metric::Info<'b>) + 'static)` cannot be shared between threads safely
   --> packages/storage_crackhouse/src/basic/mod.rs:115:17
    |
115 | static DB_LOCK: std::sync::OnceLock<DatabaseConnection> = OnceLock::new();
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn for<'a, 'b> Fn(&'a sea_orm::metric::Info<'b>) + 'static)` cannot be shared between threads safely
    |
    = help: the trait `Sync` is not implemented for `(dyn for<'a, 'b> Fn(&'a sea_orm::metric::Info<'b>) + 'static)`
    = note: required for `Arc<(dyn for<'a, 'b> Fn(&'a sea_orm::metric::Info<'b>) + 'static)>` to implement `Sync`
note: required because it appears within the type `Option<Arc<(dyn for<'a, 'b> Fn(&'a sea_orm::metric::Info<'b>) + 'static)>>`
   --> /home/p/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:600:10
    |
600 | pub enum Option<T> {
    |          ^^^^^^
note: required because it appears within the type `sea_orm::driver::rusqlite::RusqliteSharedConnection`
   --> /home/p/V/sea-orm/sea-orm-sync/src/driver/rusqlite.rs:42:12
    |
 42 | pub struct RusqliteSharedConnection {
    |            ^^^^^^^^^^^^^^^^^^^^^^^^
note: required because it appears within the type `DatabaseConnectionType`
   --> /home/p/V/sea-orm/sea-orm-sync/src/database/db_connection.rs:34:10
    |
 34 | pub enum DatabaseConnectionType {
    |          ^^^^^^^^^^^^^^^^^^^^^^
note: required because it appears within the type `DatabaseConnection`
   --> /home/p/V/sea-orm/sea-orm-sync/src/database/db_connection.rs:24:12
    |
 24 | pub struct DatabaseConnection {
    |            ^^^^^^^^^^^^^^^^^^
    = note: required for `OnceLock<DatabaseConnection>` to implement `Sync`
    = note: shared static variables must have a type that implements `Sync`

Steps to Reproduce

1. static DB_LOCK: std::sync::OnceLock<DatabaseConnection> = OnceLock::new();
2. compiler error

Expected Behavior

compile

Actual Behavior

no compile

Reproduces How Often

always

Workarounds

diff --git a/sea-orm-sync/src/metric.rs b/sea-orm-sync/src/metric.rs
index 86bf48d6..6c37fe86 100644
--- a/sea-orm-sync/src/metric.rs
+++ b/sea-orm-sync/src/metric.rs
@@ -1,6 +1,6 @@
 use std::{sync::Arc, time::Duration};
 
-pub(crate) type Callback = Arc<dyn Fn(&Info<'_>)>;
+pub(crate) type Callback = Arc<dyn Fn(&Info<'_>)+Send+Sync>;
 
 #[allow(unused_imports)]
 pub(crate) use inner::metric;

johnny-smitherson@e7492d9

Versions

same as #3068

[Huliiiiii]

Do you need to use the DatabaseConnection in a multi-threaded environment? In this case, you should use sea-orm instead of sea-orm-sync.

rusqlite::Connection is also !Sync. In a single-threaded environment, you should use OnceCell instead of OnceLock.

@tyt2y3 make sync script lacks coverage for removing Arc and Mutex from the sync crate.

[johnny-smitherson]

From my understanding only sea-orm-sync has wasm support through rusqlite, the "rusqlite" feature on sea-orm doesn't seem to be pulling that library at all.

I'm trying to keep a single code-base across browser and non-browser, so I will stick with the sync version unless the original async version starts supporting wasm32 as well.

Anyway, because of all the browser / dedicated worker / shared message passing shenanigans, I basically have two environments:

• browser worker thread which is single-threaded but async, that is wired together to sometimes require Sync
• dedicated host thread which will run all the sqlite ops in sync on a single thread local connection

I guess I'm trying to skip doing a bunch of dependency injection by hoisting stuff into shared statics.

rusqlite::Connection is also !Sync. In a single-threaded environment, you should use OnceCell instead of OnceLock.

The comment on this says it should be shared between threads, which it is, once you add the 3 lines of +Send+Sync. IDK if it breaks anything else

[Huliiiiii]

The sync version is script-generated, so comments aren’t taken into account.