Document how to use models in multi-threaded environments

[charleselie]

Hello,

I want to fill a combobox with all peripherals connected to my computer (windows), so I don't know the number of elements I have. I have tried different solutions, but I have the following problem :

NonNull<i_slint_core::sharedvector::SharedVectorInner<u8>> cannot be shared between threads safely within [slint::SharedString], the trait Sync is not implemented for NonNull<i_slint_core::sharedvector::SharedVectorInner<u8>> required because it appears within the type [SharedString] required for &[slint::SharedString] to implement std::marker::Send

how can I safely change my combobox depending on the USB peripherals I am connecting to my computer ?

[ogoffart]

Thanks for opening an issue. Please paste more code of what you're trying to do. SharedVector and SharedString should be Send, but are not Sync.
Maybe you need to use a Mutex. Or maybe you need to use slint::invoke_from_event_loop to pass the data back to the UI thread.

[charleselie]

hello,

I've tried to send a sharedVector or sharedString but I have the previous error. I'am actually using the event_loop to update my combobox.

the code ( that is not the same anymore), is working, but as soon as I want to pass the vector, it doesn't not work:

    println!("filling combo box");
    let mut device_names_SS: Vec<SharedString> = Vec::new();
    
    for i in 0.. device_names.len()
    {
        device_names_SS.push(device_names[i].clone().into());
    }

    println!("device_names__ss list {}", device_names_SS[0].clone());
         
    window_weak.upgrade_in_event_loop(move |window| 
    {
        window.set_usbList([device_names_SS[0].clone()].into());

    }).unwrap();

[nununoisy]

The types are a bit confusing, but this is possible. Here's a snippet that will convert any iterable container into a Slint model:

fn slint_string_arr<I>(a: I) -> slint::ModelRc<SharedString>
    where
        I: IntoIterator,
        I::Item: Into<SharedString>
{
    let shared_string_vec: Vec<SharedString> = a
        .into_iter()
        .map(|s| s.into())
        .collect();
    ModelRc::new(VecModel::from(shared_string_vec))
}
// then...
window_weak.upgrade_in_event_loop(move |window| {
    window.set_usbList(slint_string_arr(device_names.clone()))
}).unwrap();

Perhaps this conversion could be provided by Slint itself to simplify usecases like these.

[ogoffart]

Perhaps this conversion could be provided by Slint itself to simplify usecases like these.

In this case, it should be as simple as:

window_weak.upgrade_in_event_loop(move |window|   {
        window.set_usbList(ModelRc::new(VecModel::from(device_names_SS)));
    }).unwrap();

Maybe there could be some simplification for this parent to convert a Vec to a ModelRc directly, or maybe we need better documentation somehow?

[tronical]

It is nowadays a rather common use-case to collect data in separate threads, with the objective of feeding the final data into models. Our documentation for Models - for example at https://slint.dev/releases/1.3.2/docs/rust/slint/struct.ModelRc#example - could include instructions how this is best done, i.e. how to deal with !send errors and the like.

[charleselie]

The types are a bit confusing, but this is possible. Here's a snippet that will convert any iterable container into a Slint model:

fn slint_string_arr<I>(a: I) -> slint::ModelRc<SharedString>
    where
        I: IntoIterator,
        I::Item: Into<SharedString>
{
    let shared_string_vec: Vec<SharedString> = a
        .into_iter()
        .map(|s| s.into())
        .collect();
    ModelRc::new(VecModel::from(shared_string_vec))
}
// then...
window_weak.upgrade_in_event_loop(move |window| {
    window.set_usbList(slint_string_arr(device_names.clone()))
}).unwrap();

Perhaps this conversion could be provided by Slint itself to simplify usecases like these. I am back on that project, and perfect this work well. Thanks a lot. I was doing it another way around, but this is better.

However this following solution doesn't work : window.set_usbList(ModelRc::new(VecModel::from(device_names_SS)));

I think it could be very usefull to have an easy way .