A go worker pattern

AsynchronousWork_and_SerialOutput.go

token := make(chan struct{}, 1)
token <- struct{}{} // A goroutine must have the token to print

for test := range readTests(os.Stdin) {
	gate <- struct{}{}
	next := make(chan struct{}, 1) // where to send the token to.
	go func(test Test, in, out chan struct{}) {
		defer func() { <-gate }()

		// Asynchronous work.
		time.Sleep(1 * time.Second)

		// This bit enforces running in the order we started
		t := <-in // wait for token to become available
		defer func() {
			out <- t // give token to next worker
		}()

        	// Runs in serial, in input order.
		log.Printf("Ran %v", test)
	}(test, token, next)
	token = next // becomes the next token.
}