How can I make dispatching concurrent?

[Architector4]

So, with Teloxide 0.11.1, I have this code:

use teloxide::prelude::*;
#[tokio::main]
async fn main() {
    let bot = Bot::from_env();

    let handler = Update::filter_message().endpoint(
            |bot: Bot, msg: Message| async move {
                bot.send_message(msg.chat.id, "A").await?;
                tokio::time::sleep(tokio::time::Duration::from_secs(3)).await;
                bot.send_message(msg.chat.id, "B").await?;
                respond(())
            },
        );
    Dispatcher::builder(bot, handler)
        .enable_ctrlc_handler()
        .build().dispatch().await;
}

From everything being async/await, I expected this to run the endpoint closure concurrently for each message. For example, if I send two messages to the bot in quick succession, I expect it to send "A" twice, and after about 3 seconds send "B" twice.

However, that seems to not be the case: it sends "A", then waits 3 seconds, sends "B", then sends "A" immediately after, and sends "B" after another 3 seconds.

I don't know if this behavior is present with teloxide::repl, but I need to perform more functions than to receive messages with what I'm trying to do, so I have to use dispatching here.

Is there a way to achieve this same behavior, but have the endpoint closure be run concurrently?

[Hirrolot]

From the Dispatcher documentation:

Updates from different chats are handled concurrently, whereas updates from the same chats are handled sequentially. If the dispatcher is unable to determine a chat ID of an incoming update, it will be handled concurrently. Note that this behaviour can be altered with distribution_function.

Because you communicate with your bot in the same chat, all your updates are handled sequentially, which works as designed. If you want to override this behaviour, you can do it through aforestated distribution_function. In particular, if you want all updates to be handled concurrently, just return None from this function.

[Architector4]

Oh, I completely missed that. Adding .distribution_function::<bool>(|_| None) to the builder solves it. Thanks!

[WaffleLapkin]

As a small nit, you can actually help compiler a little bit, by saing that you can only ever return None from the function:

.distribution_function(|_| None::<std::convert::Infallible>)

[Hirrolot]

Maybe it's worth adding concurrent_distribution_fn to the public API with such a body?

[WaffleLapkin]

Well, default behavior is also concurrent, given different chats. Maybe we can come up with a better name.

But yeah, I can see such function being useful, we can add it.