ref: 183f3d40a1dbc2254f1e01de21eb022996f40ad2
dir: /lib/thread/test/waitgrp.myr/
use std
use thread
const Threadc = 8
var wg
const main = {
	wg = thread.mkwg(Threadc)
	for var i = 0; i < Threadc; i++
		thread.spawn({
			std.usleep(3_000_000)
			thread.wgpost(&wg)
			thread.wgwait(&wg)
		})
	;;
	thread.wgwait(&wg)
}