Compile error 'Sync is not implemented' under tokio

[tqwewe]

Related issue: SeaQL/sea-query#105

With the following function in a tokio async runtime, I get an error saying:

future created by async block is not `Send`
help: the trait `Sync` is not implemented for `(dyn Iden + 'static)`

async fn update(
    db: &DatabaseConnection,
    active_model: model::ActiveModel,
) -> Result<bool, Box<dyn std::error::Error>> {
    Entity::update(active_model)
        .exec(db)
        .await
        .map_err(Box::new)?;

    Ok(true)
}

SeaORM does not seem to be thread safe. Perhaps this is due to sea-query's Iden type.

[tyt2y3]

Can you setup an minimal reproducible example under /examples?

[tqwewe]

I've fixed it locally... the quick fix seems to be changing the definition of trait Iden in sea-query to:

pub trait Iden: Send + Sync {
    ...
}

This is to enforce the type is Sync

[tyt2y3]

Great finding. Can we instead do it inside SeaORM, changing IdenStatic instead of Iden?

pub trait IdenStatic: Iden + Copy + Debug + Send + Sync + 'static {

I am trying to understand the problem

[tqwewe]

I've tried removing Send + Sync from Iden trait in sea-query and adding it to IdenStatic like you suggested, but the errors come back.

T inside Arc<T> should be Send + Sync for the whole Arc to be Send + Sync.
https://doc.rust-lang.org/std/sync/struct.Arc.html#thread-safety
It says:

Arc<T> will implement Send and Sync as long as the T implements Send and Sync. Why can’t you put a non-thread-safe type T in an Arc<T> to make it thread-safe? This may be a bit counter-intuitive at first: after all, isn’t the point of Arc<T> thread safety? The key is this: Arc<T> makes it thread safe to have multiple ownership of the same data, but it doesn’t add thread safety to its data.

Perhaps sea-query should add Send + Sync to the Iden trait only if "thread-safe" flag is enabled.

[tyt2y3]

Okay, good to know. Thanks.

[tyt2y3]

Btw, any idea how can I add a test case to our test suite for this?
Because it worked in our async_std examples.
It might be specific to tokio?

[tqwewe]

Btw, any idea how can I add a test case to our test suite for this?

Perhaps just making a tokio app and executing your query in a tokio spawned task:

tokio::spawn(async move {
    MyEntity::find().one(&db).await;
})
.await;

It might be specific to tokio?

Perhaps... but I think it might just be any app that uses multiple threads.

[tyt2y3]

@billy1624 can we also run our test suite using tokio?

[billy1624]

Planning to do so. Running doctest & unit test on all supported runtime.

[billy1624]

Planning to do so. Running doctest & unit test on all supported runtime.

See #91

[tyt2y3]

I verified that enabling thread-safe on SeaQuery did solve the issue.