ref: bb49af4578c4a1f31beee9da6d868e859697d1bc
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)
}