这是什么语法啊，看不懂

系统库 signal.go 中有这么一段代码： // Wait until there are no more signals waiting to be delivered. // Defined by the runtime package. func signalWaitUntilIdle() //<-------------这里看不懂啊，我自己尝试模仿一个，报错说函数必须有函数体 func process(sig os.Signal) { n := signum(sig) if n < 0 { return } handlers.Lock() defer handlers.Unlock() for c, h := range handlers.m { if h.want(n) { // send but do not block for it select { case c <- sig: default: } } } // Avoid the race mentioned in Stop. for _, d := range handlers.stopping { if d.h.want(n) { select { case d.c <- sig: default: } } } }