Go, tcp too many open files debug

Question

Here\'s a straightforward Go http (tcp) connection test script

func main() {
    ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *htt         


        

Answer 1

If you want to run millions of go routines that open/read/close a socket, well you better up your ulimit, or open/read/close the socket and pass the value read in to the go-routine, but I would use a buffered channel to control how many file descriptors you want to be able to open.

const (
    // this is where you can specify how many maxFileDescriptors
    // you want to allow open
    maxFileDescriptors = 100
)

func main() {
    ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintln(w, "Hello, client")
    }))
    defer ts.Close()
    var wg sync.WaitGroup
    maxChan := make(chan bool, maxFileDescriptors)
    for i := 0; i < 1000; i++ {
        maxChan <- true
        wg.Add(1)
        go func(url string, i int, maxChan chan bool, wg *sync.WaitGroup) {
            defer wg.Done()
            defer func(maxChan chan bool) { <-maxChan }(maxChan)
            resp, err := http.Get(url)
            if err != nil {
                panic(err)
            }
            greeting, err := ioutil.ReadAll(resp.Body)
            if err != nil {
                panic(err)
            }
            err = resp.Body.Close()
            if err != nil {
                panic(err)
            }
            fmt.Printf("%d: %s", i, string(greeting))
        }(ts.URL, i, maxChan, &wg)
    }
    wg.Wait()
}