我们是否应该为每个异步请求运行一个goroutine，即使它们是彼此产生的呢？

Question

I'm developing a web application in go and I know in http package, every request is run in a separate goroutine. Now, if the code inside this goroutine queries a database then wait and using db result calls a remote api to fetch some related data and son on and so forth, shall I run each of these calls in separate goroutine or the one provided by http is enough?

Answer 1

That depends on what you're doing.

Each HTTP request should be handled sequentially. That is to say, you shouldn't fire off a goroutine for handling the request itself:

func myHandler(w http.ResponseWriter, r *http.Request) {
    go func(w http.ResponseWriter, r *http.Request) {
        // There's no advantage to this
    }(w,r)
}

However, there are still times when goroutines make sense when handling an HTTP response. The two most common situations are probably:

1. You want to do something in parallel.

   func myHandler(w http.ResponseWriter, r *http.Request) {
       wg := &sync.WaitGroup{}
       wg.Add(2)
       go func() {
           defer wg.Done()
           /* query a remote API */
       }()
       go func() {
           defer wg.Done()
           /* query a database */
       }()
       wg.Wait()
       // finish handling the response
   }
   

2. You want to finish handling something after responding to the HTTP request, so that the web client doesn't have to wait.

   func myHandler(w http.ResponseWriter, r *http.Request) {
       // handle request
       w.Write( ... )
       go func() {
           // Log the request, and send an email
       }()
   }