Async Function is Not Sync Debugging

I am trying to build a simple "scheduler" in an asynchronous context. Here is a piece of the some sample code that will not compile because the Future is "not sync". What I don't understand is...why is it not sync? I am using an Arc<RwLock> for the data structures that I'm using. I can't even access them without locking, so why am I not Sync?

Here is the example code:

async fn testing_theory(mut thing: JobScheduler) -> Result<(), JobError>
    let other_job = Job::new_one_shot(Duration::from_secs(20), |_uuid, _l| Box::pin(async move { println!("Extra"); Ok(()) }))?;

async fn main() -> Result<(), Box<dyn std::error::Error + 'static>> {
    let mut sched = JobScheduler::create();

    let four_s_job_async = Job::new_cron_job("1/4 * * * * *", |_uuid, l| Box::pin(async move {
        println!("{:?} I am a cron job run async every 4 seconds", chrono::Utc::now());
        let job_catch = l.clone();
    let four_s_job_guid = four_s_job_async.get_job_id().await;

And here is the error I'm getting:
error: future cannot be shared between threads safely
--> examples/
15 | let four_s_job_async = Job::new_cron_job("1/4 * * * * *", |_uuid, l| Box::pin(async move {
| ____________________________________________________________________^
16 | | println!("{:?} I am a cron job run async every 4 seconds", chrono::Utc::now());
17 | | let job_catch = l.clone();
18 | | testing_theory(job_catch).await;
19 | | Ok(())
20 | | }))?;
| |
^ future created by async block is not Sync
= help: the trait Sync is not implemented for dyn Future<Output = Result<(), JobError>> + Send
note: future is not Sync as it awaits another future which is not Sync
--> examples/
7 | thing.add(other_job).await.unwrap();
| ^^^^^^^^^^^^^^^^^^^^ await occurs here on type Pin<Box<dyn Future<Output = Result<(), JobError>> + Send>>, which is not Sync
= note: required for the cast to the object type dyn Future<Output = Result<(), JobError>> + Send + Sync

If someone can help me with the error, I'd appreciate it, but I'm mostly interested do I debug this? How do I figure out what variable or situation is causing the Sync error?

Thank you

There's generally no need for a future to implement Sync because the Sync trait only really makes sense for things with &self methods, but the only method on a future takes &mut self. My guess is that the cron job thing you are using is unnecessarily requiring Sync somewhere it shouldn't.

Also: please put errors in code blocks - they're much easier to read that way

Thanks alice. It does indeed seem like there are some extra Sync parameters. Removing them introduces some new problems, that I'm going to try and get around with a code refactor.

Thanks again. I'll put the errors in code blocks in the future.

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