With async/await the apparent complexity gets reduced at the cost of vastly increased actual complexity. E.g., now instead of everything being your code that you can look at and reason about, all your concurrent workloads disappear in this void that promises to do the right thing with them. If it works the way you intended, great. If it doesn't, the rabbit hole can now be really deep.
And then, it's also a trust issue. Now you have to trust other people to have done a good job.
Ok, yes, this makes sense.
And the loss of control is also an issue for me. I write code for memory-constrained environments, with blocking code and OS threads I can usually bound my memory consumption fairly easily. If I surrender the control to a scheduler runtime I feel like it becomes a lot harder, although here I'm willing to concede that it might have more to do with my lack of experience with Tokio than an objective issue.
fn read(&mut self, buf: &mut [u8]) -> Result<usize, io::Error>
fn read<T: AsMut<[u8]>>(self, buf: T) ->
impl Future<Item = (Self, T, usize), Error = (Self, T, io::Error)>
I recently tried writing a small program that would manually poll a future to get a feel for it - utter disaster. conflicting versions of tokio, compiles but crashes because something is called outside of the tokio runtime context, etc. all the examples have #[tokio::main]-decorated main - it's like, I'm not giving you my #$(&#@(&ing main function! the programs I write have tons of stuff going on! I can't just give some library my entire control flow!
sorry for the rant! felt good to write it though.
that is ... not how I have experienced it. I work on building highly concurrent systems every day but async drives me insane. to me the fundamental issue is that although the code now reads linearly, it no longer executes linearly (or reasonably close to linearly), which is 1000x more confusing.
the other thing, when I'm using rust to build something high performance, part of the reason is it provides greater control. I just can't square that with macro-decorating my main function, and handing over the core control-flow to someone else's runtime.