Zio - async I/O framework based on libxev

Calder-Ty · November 3, 2025, 8:05pm

9 posts were split to a new topic: Thoughts on AI Coding

lalinsky · November 4, 2025, 12:30pm

I’ve refactored the coroutine code to be completely standalone, not depending on anything else inside zio, in case anybody wants to use it. Could even turn it into a library on its own. Also added RISC V support. And had a little fun implementing tiny channel for ping-pong test. Stack reservation on virtual memory will be a part of this standalone lib soon.

github.com/lalinsky/zio

src/coroutines.zig

main

// zig fmt: off
// SPDX-FileCopyrightText: 2025 Lukáš Lalinský
// SPDX-License-Identifier: Apache-2.0

const std = @import("std");
const print = std.debug.print;
const Allocator = std.mem.Allocator;
const builtin = @import("builtin");
const assert = std.debug.assert;

pub const DEFAULT_STACK_SIZE = if (builtin.os.tag == .windows) 2 * 1024 * 1024 else 256 * 1024; // 2MB on Windows, 256KB elsewhere - TODO: investigate why Windows needs much more stack

pub const stack_alignment = 16;
pub const Stack = []align(stack_alignment) u8;
pub const StackPtr = [*]align(stack_alignment) u8;

const WindowsTIB = extern struct {
    fiber_data: u64, // TEB offset 0x20
    deallocation_stack: u64, // TEB offset 0x1478
    stack_base: u64, // TEB offset 0x08

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lalinsky · November 4, 2025, 6:42pm

This took a bit of refactoring, to satisfy the way std.Io wants to do closures, but I have the first version of async/concurrent/await/cancel working. Now that I have this done, I/O operations should go much quicker. The zig-0.16 branch has a long way to go though, as std.posix is being removed and the code in libxev depends on it.

lalinsky · November 10, 2025, 1:59pm

I spun off this project, my effort to replace libxev in zio. There are many reasons for which I’d prefer something slightly different from libxev: consistency of cancelations, immediate timer changes on all backends, wasted stack space, better handling of vectord reads/writes. What got me working on this is actually Zig 0.16 migration, as std.posix is being dismantled, it would be very difficult to upgrade libxev, so I decided to take it a step further and completely replace it, while making the new design a better fit for zio. It supports Linux, Windows, macOS, FreeBSD and NetBSD. Currently missing IOCP backend for Windows, but I don’t think that’s a huge problem, as I expect Windows will be used only as platform for development, not deployment. I’m also planning to make it multi-threading aware, to help with thread pinning in the zio runtime, because that depends on backend specifics.

This is the project:

The code it needs you to write is very verbose, it should not be used directly:

github.com/lalinsky/aio.zig

src/test/stream_server.zig

main

const std = @import("std");
const builtin = @import("builtin");
const Loop = @import("../loop.zig").Loop;
const Backend = @import("../backend.zig").Backend;
const Completion = @import("../completion.zig").Completion;
const NetOpen = @import("../completion.zig").NetOpen;
const NetBind = @import("../completion.zig").NetBind;
const NetListen = @import("../completion.zig").NetListen;
const NetAccept = @import("../completion.zig").NetAccept;
const NetConnect = @import("../completion.zig").NetConnect;
const NetRecv = @import("../completion.zig").NetRecv;
const NetSend = @import("../completion.zig").NetSend;
const NetShutdown = @import("../completion.zig").NetShutdown;
const NetClose = @import("../completion.zig").NetClose;
const net = @import("../os/net.zig");
const time = @import("../os/time.zig");

pub fn EchoServer(comptime domain: net.Domain, comptime sockaddr: type) type {
    return struct {
        state: State = .init,

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lalinsky · November 13, 2025, 11:59am

Extracted another library from the code. It’s beneficial to have more extensive CI testing here, so I moved it out of zio. Could be also used by someone else if they want to experiment.

KilianHanich · November 14, 2025, 12:07am

To add, apparently glibc has getaddrinfo_a.

FreeBSD has the getdns library, even if that’s not part of their libc.

OpenBSD has getaddrinfo_async, but it seems like andrewrk has already found it since searching openbsd getaddrinfo_async shows an issue in Zig about it as top result on my end.

Windows has DnsQueryEx.