many_filters.zig

const std = @import("std");
const Channel = std.event.Channel;
const Timer = std.time.Timer;
const warn = std.debug.warn;

pub const io_mode = .evented;

// Send the sequence 2, 3, 4, ... to channel 'ch'.
fn generate(ch: *Channel(u32)) void {
    var i: u32 = 2;
    while (true) : (i += 1) {
        ch.put(i);
    }
}

// Copy the values from channel 'in' to channel 'out',
// removing those divisible by 'prime'.
fn filter(in: *Channel(u32), out: *Channel(u32), prime: u32) void {
    while (true) {
        const i = in.get();
        if (i % prime != 0) {
            out.put(i);
        }
    }
}

// The prime sieve: Daisy-chain Filter processes.
pub fn main() anyerror!void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    const allocator = &arena.allocator;
    
    var primesish = try allocator.alloc(u32, 100000);

    var timer = try Timer.start();

    var ch = try allocator.create(Channel(u32));
    ch.init(&[0]u32{}); // Unbuffered channel.
    
    _ = async generate(ch);

    var i: usize = 0;
    while (i < 100) : (i += 1) {
        const prime = ch.get();
        primesish[i] = prime;

        const ch1 = try allocator.create(Channel(u32));
        ch1.* = undefined;
        ch1.init(&[0]u32{});

        const frame = try allocator.create(@Frame(filter));
        frame.* = undefined;
        frame.* = async filter(ch, ch1, prime);
        ch = ch1;
    }
    
    while (i < primesish.len) : (i += 1) {
        primesish[i] = ch.get();
    }
    
    const time = timer.lap();
    
    warn("Zig took {d:.3}s", .{@intToFloat(f64, time) / 1000000000.0});
}

This example is broken, due to channels interacting with the event loop to run async on multiple threads. A better version can be found at https://gist.github.com/SpexGuy/953e5780cd2d2c524cba6a79f13076e6