TypeScript,
compiled
to native.

import { go, Channel, select, defaultCase } from 'klain:sync'

const primes = new Channel<number>(1024)  // primes stream to the collector
const done = new Channel<number>(0)        // a worker signals when finished

// Fan out: 8 goroutines test interleaved slices, in parallel on every core.
for (let id = 0; id < 8; id++) {
  go(() => {
    for (let n = 2 + id; n <= 500000; n += 8) {
      if (isPrime(n)) primes.send(n)
    }
    done.send(id)
  })
}

// Fan in: select takes whichever channel is ready — count primes as they
// arrive, tally completions, then drain the last buffered results.
let count = 0, finished = 0
while (finished < 8) {
  select(
    primes.recvCase((p: number) => { count += 1 }),
    done.recvCase((id: number) => { finished += 1 }),
  )
}
let draining = true
while (draining) {
  select(
    primes.recvCase((p: number) => { count += 1 }),
    defaultCase(() => { draining = false }),
  )
}
console.log(`primes below 500000: ${count}`)  // 41538