go上下文管理-context

context的应用

1 .ctx可以继承
2 .超时控制

package main

import (
	"context"
	"fmt"
	"io/ioutil"
	"net/http"
	"time"
)
type Result struct {
	r   *http.Response
	err error
}
func process() {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	tr := &http.Transport{}
	client := &http.Client{Transport: tr}
	c := make(chan Result, 1)
	req, err := http.NewRequest("GET", "http://www.baidu.com", nil)
	if err != nil {
		fmt.Println("http request failed, err:", err)
		return
	}
	go func() {
		resp, err := client.Do(req)
		pack := Result{r: resp, err: err}
		c <- pack
	}()
	select {
	//超时时，从ctx.Done中读出数据，走此分支
	case <-ctx.Done():
		tr.CancelRequest(req)
		res := <-c
		fmt.Println("Timeout! err:", res.err)
	case res := <-c:
		defer res.r.Body.Close()
		out, _ := ioutil.ReadAll(res.r.Body)
		fmt.Printf("Server Response: %s", out)
	}
	return
}
func main() {
	process()
}

3 .保存上下文