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I just upgraded some code to Zig 0.16.0 and I am actually really happy with the results. It impacted A LOT of things, but the changes were actually very good and seems to have set the language for a bright future, especially with the new IO mechanism which allows supper efficient code that looks good whether it's implemented single-threaded, multi-threaded or just via an event loop!

If you haven't tried Zig since 0.16.0 was released, I highly recommend having a look. The release notes for this release were huge!!

https://ziglang.org/download/0.16.0/release-notes.html

ulbu 7 hours ago [ - ]

the “(super) efficient” is not there yet. Io is still dynamic dispatch with multiple layers of indirection. afaik it’s slower than before.

the upcoming releases are expected to provide a solution to this “dispatch is comptime-known, but still dynamic” problem, and drop the loses in efficiency.

bbkane 6 hours ago [ - ]

Hmm in the 2025 talk ( https://youtu.be/f30PceqQWko?si=qZESxMaSyt7fYMfz ), Andrew emphasizes that this approach is more efficient than before- even showing compiled assembly iirc. I guess that was a one-off?

chaz72 5 hours ago [ - ]

My guess is that one of these (Andrew) is measuring syscalls and the other is measuring vtable indirections.

kristoff_it 3 hours ago [ - ]

A vtable indirection is essentially free when you're going to perform a syscall. What matters is that the buffer is above the vtable (which is already the case for the current implementation) so that you don't pay for the indirection when hitting the buffer.

nullpoint420 4 hours ago [ - ]

Wow that’s gnarly it’s using dynamic dispatch. I mean I get it, but I thought zig was some sort of performance demon.

smj-edison an hour ago [ - ]

I believe their plan is using "restricted function pointers", where you can specify that a pointer will only ever be to a function defined in the codebase. I'm pretty sure they also have plans for devirtualization, but I haven't followed super closely.

dnautics 3 hours ago [ - ]

if youre doing io, one pointer indirection seems unlikely tp be rate limiting. same for allocation (the other dynamic dispatch in zig)

rsyring 6 hours ago [ - ]

The parent seems to be talking about efficient code style, not necessarily performance implementation, as they go on to discuss how it looks.

That is, I think the point was DevX not io performance.

tarruda 2 hours ago [ - ]

> especially with the new IO mechanism which allows supper efficient code that looks good whether it's implemented single-threaded, multi-threaded or just via an event loop!

I had some trouble understanding how the async/await mechanism works:

  var foo_future = io.async(foo, .{args});
  defer if (foo_future.cancel(io)) |resource| resource.deinit() else |_| {}

  var bar_future = io.async(bar, .{args});
  defer if (bar_future.cancel(io)) |resource| resource.deinit() else |_| {}

  const foo_result = try foo_future.await(io);
  const bar_result = try bar_future.await(io);

My assumption is that calling io.async using an event loop implementation of IO, it will internally start a "task" (or whatever it should be called) and that the future is a handle to it. So far so good.

The part that I don't understand is what happens when you call future.await(io). Will the IO implementation somehow suspend the current function and resume once the future is resolved? If so, does that mean that every function in zig is a stackless coroutine?

kristoff_it an hour ago [ - ]

> If so, does that mean that every function in zig is a stackless coroutine?

No and yes.

If you're using Io.Threaded, then the concurrency model is multithreading and calling Future.await will block your thread on a OS futex.

If you're using Io.Evented, then the concurrency model is green threads / fibers and calling Future.await will suspend the current green thread by yielding (swapping CPU state with another fiber).

Zig currently does not support stackless coroutines so today you can't have that, but we used to have them (pre self-hosted compiler), and there's an accepted proposal to bring them back, in which case any function that calls await, or that otherwise has a suspension point, would have to be transformed into a stackless coroutine by the compiler, yes. The plan is for that to happen transparently without requiring an `async` annotation in the function signature, like we already did in the past.

This is an old post of mine that explains how that worked at a high level: https://kristoff.it/blog/zig-colorblind-async-await/

jasonjmcghee 2 hours ago [ - ]

For future reference you can format code on hn with a newline first then indenting each line by 2+ spaces. (Rather than triple tick)

tarruda an hour ago [ - ]

Fixed it. thanks!

afirmativ 5 hours ago [ - ]

Maybe one day it'd be possible to use these new features, but I find myself using `.use_llvm = true` in my zig builds for stability and lesser tested targets.