Replace gtk3 with gtk4

[zhao-gang]

Fixed #227

[PolyMeilex]

GTK does not support multithreading, so those changes seem to be untested, and will most likely simply panic on threading assertions at runtime.

[zhao-gang]

Hi @PolyMeilex , how to test GTK4 with multithreading ? I run examples with GTK4 feature and they seemed okay.

[PolyMeilex]

My guess is that simply opening the async dialog more than once during the same process lifetime should do the trick, and cause the process to blow up in one way or another. So either open 2 dialogs, or open one and the next one once the first one is done.

[zhao-gang]

Modified async example to open 2 dialogs in sequence and it's working. Added my testing code.

Yes it crashed with GTK. I'll try to fix the async code.

fn main() {
    // Spawn dialog on main thread
    let task1 = rfd::AsyncFileDialog::new().pick_file();
    let task2 = rfd::AsyncFileDialog::new().pick_file();

    // Await somewhere else
    execute(async {
        let file = task1.await;

        if let Some(file) = file {
            // If you are on native platform you can just get the path
            #[cfg(not(target_arch = "wasm32"))]
            println!("{:?}", file.path());

            // If you care about wasm support you just read() the file
            file.read().await;
        }

        let file = task2.await;

        if let Some(file) = file {
            // If you are on native platform you can just get the path
            #[cfg(not(target_arch = "wasm32"))]
            println!("{:?}", file.path());

            // If you care about wasm support you just read() the file
            file.read().await;
        }
    });

    std::thread::park();
}

use std::future::Future;

#[cfg(not(target_arch = "wasm32"))]
fn execute<F: Future<Output = ()> + Send + 'static>(f: F) {
    // this is stupid... use any executor of your choice instead
    std::thread::spawn(move || futures::executor::block_on(f));
}
#[cfg(target_arch = "wasm32")]
fn execute<F: Future<Output = ()> + 'static>(f: F) {
    wasm_bindgen_futures::spawn_local(f);
}

[zhao-gang]

Hi @PolyMeilex , I think the GTK multithreading issue is fixed. And updated async test to check this.