Question about using in rust

[cheunglok97]

#[tokio::main]
async fn main() {
    let handle = tokio::spawn(async {
        evaluate().await;
    });
    let handle2 = tokio::spawn(async {
        evaluate().await;
    });
    let (result, result2) = tokio::join!(handle, handle2);
}

async fn evaluate() {
    let decision_content: DecisionContent = serde_json::from_str(include_str!("jdm_graph.json")).unwrap();
    let engine = DecisionEngine::default();
    let decision = engine.create_decision(decision_content.into());

    let result = decision.evaluate(&json!({ "input": 12 })).await;
}

I am trying to studying this project and I and faced some problem when I try it.

Then I compile the above code, I got
Rc<UnsafeCell<Vec<&zen_expression::opcodes::Opcode<'_>>>> cannot be sent between threads safely`

May I know how to sove this?

Great thanks!

[stefan-gorules]

Hi @cheunglok97,

ZEN expressions are optimized for single-threaded use and don't support multi-threading in the evaluation of a single expression. This limitation applies to the ZEN engine as well.

To integrate ZEN decisions within a Tokio-based, multi-threaded environment, you can use Handle::current().block_on to execute these decisions synchronously within an asynchronous context. This approach bypasses Tokio's thread safety requirements for asynchronous functions, allowing you to include non-thread-safe ZEN operations in your Tokio application. For a practical implementation, see this GitHub example.

Let me know if this solves your issue.

[cheunglok97]

Thanks! That is a very good example

[andymk-dev]

This worked earlier but it doesn't seem to work with the latest version (0.33). I'm getting the following error again.

std::rc::Rc<str> cannot be sent between threads safely
within std::result::Result<zen_engine::DecisionGraphResponse, std::boxed::Box<zen_engine::EvaluationError>>, the trait std::marker::Send is not implemented for std::rc::Rc<str>, which is required by std::result::Result<zen_engine::DecisionGraphResponse, std::boxed::Box<zen_engine::EvaluationError>>: std::marker::SendrustcClick for full compiler diagnostic
mod.rs(21, 10): required because it appears within the type zen_engine::Variable
graph.rs(441, 12): required because it appears within the type zen_engine::DecisionGraphResponse
result.rs(527, 10): required because it appears within the type std::result::Result<zen_engine::DecisionGraphResponse, std::boxed::Box<zen_engine::EvaluationError>>
blocking.rs(205, 12): required by a bound in tokio::task::spawn_blocking