In this program:
</p>

<pre>
var a string
var once sync.Once

func setup() {
	a = "hello, world"
}

func doprint() {
	once.Do(setup)
	print(a)
}

func twoprint() {
	go doprint()
	go doprint()
}
</pre>

<p>
calling <code>twoprint</code> will call <code>setup</code> exactly
once.
The <code>setup</code> function will complete before either call
of <code>print</code>.