发出HTTP请求时打开的文件过多

Question

I am trying to create a http client program in go which would make many http GET requests. I am using a buffered channel to limit the number of concurrent requests.

When I run the program I get

Get http://198.18.96.213/: dial tcp 198.18.96.213:80: too many open files

Here is my program:

package main

import (
    "fmt"
    "net/http"
    "time"
)

func HttpGets(numRequests int, numConcurrent int, url string) map[int]int {
    // I want number of requests with each status code
    responseStatuses := map[int]int {
        100: 0, 101 : 0, 102 : 0, 200 : 0, 201 : 0, 202 : 0, 203 : 0, 204 : 0, 205 : 0, 
        206 : 0, 207 : 0, 208 : 0, 226 : 0, 300 : 0, 301 : 0, 302 : 0, 303 : 0, 304 : 0, 
        305 : 0, 306 : 0, 307 : 0, 308 : 0, 400 : 0, 401 : 0, 402 : 0, 403 : 0, 404 : 0, 
        405 : 0, 406 : 0, 407 : 0, 408 : 0, 409 : 0, 410 : 0, 411 : 0, 412 : 0, 413 : 0, 
        414 : 0, 415 : 0, 416 : 0, 417 : 0, 421 : 0, 422 : 0, 423 : 0, 424 : 0, 425 : 0, 
        426 : 0, 427 : 0, 428 : 0, 429 : 0, 430 : 0, 431 : 0, 500 : 0, 501 : 0, 502 : 0, 
        503 : 0, 504 : 0, 505 : 0, 506 : 0, 507 : 0, 508 : 0, 509 : 0, 510 : 0, 511 : 0, 
    }

    reqsDone := 0
    ch := make(chan *http.Response, numConcurrent)
    for i := 0; i < numRequests; i++ {
        go func(url string) {
            client := &http.Client{}
            req, reqErr := http.NewRequest("GET", url, nil)
            if reqErr != nil {
                fmt.Println(reqErr)
            }
            // adding connection:close header hoping to get rid 
            // of too many files open error. Found this in http://craigwickesser.com/2015/01/golang-http-to-many-open-files/           
            req.Header.Add("Connection", "close") 

            resp, err := client.Do(req)
            if (err !=nil) {
                fmt.Println(err)
            }
            ch <- resp

        }(url)
    }

    for {
        select {
        case r := <-ch:
            reqsDone += 1 // probably needs a lock?
            status := r.StatusCode          
            if _, ok := responseStatuses[status]; ok {
                responseStatuses[status] += 1           

            } else {
                responseStatuses[status] = 1
            }
            r.Body.Close() // trying to close body hoping to get rid of too many files open error 
            if (reqsDone == numRequests) {
                return responseStatuses
            }    
        }
    }
    return responseStatuses
}

func main() {
    var numRequests, numConcurrent = 500, 10
    url := "http://198.18.96.213/"
    beginTime := time.Now()
    results := HttpGets(numRequests, numConcurrent, url)
    endTime := time.Since(beginTime)
    fmt.Printf("Total time elapsed: %s
", endTime)
    for k,v := range results {
        if v!=0 {
            fmt.Printf("%d : %d
", k, v)
        }       
    }

}

How to I ensure files/socets are closed so that I don't get this error when making multiple requests?

Answer 1

Basically you were spawning 100s of goroutines that will start the connection the block until they are closed.

Here's a quick (and very ugly) working code:

var (
    responseStatuses = make(map[int]int, 63)
    reqsDone         = 0

    urlCh = make(chan string, numConcurrent)
    ch    = make(chan *http.Response, numConcurrent)
)
log.Println(numConcurrent, numRequests, len(responseStatuses))
for i := 0; i < numConcurrent; i++ {
    go func() {
        for url := range urlCh {
            client := &http.Client{}
            req, reqErr := http.NewRequest("GET", url, nil)
            if reqErr != nil {
                fmt.Println(reqErr)
            }
            // adding connection:close header hoping to get rid
            // of too many files open error. Found this in http://craigwickesser.com/2015/01/golang-http-to-many-open-files/
            req.Header.Add("Connection", "close")

            resp, err := client.Do(req)
            if err != nil {
                fmt.Println(err)
            }
            ch <- resp
        }

    }()
}
go func() {
    for i := 0; i < numRequests; i++ {
        urlCh <- url
    }
    close(urlCh)
}()

<kbd>playground</kbd>