英文:
Defer never called when writing to channel
问题
我正在尝试在goroutine函数的最后一个操作中向通道写入数据。
不幸的是，这并没有起作用，而且等待组永远不会完成。
import (
"sync"
"github.com/SlyMarbo/rss"
"fmt"
)
func main() {
urls := []string{"http://rss.cnn.com/rss/edition.rss", "http://rss.time.com/web/time/rss/top/index.xml"}
var c = make(chan string)
var wg sync.WaitGroup
for _, url := range urls {
wg.Add(1)
go receiveRss(url, &wg, c)
}
wg.Wait()
fmt.Println("==============DONE=================")
}
func receiveRss(url string, wg *sync.WaitGroup, c chan string) {
defer wg.Done()
feed, err := rss.Fetch(url)
if err != nil {
fmt.Println("Failed to retrieve RSS feed", err)
}
items := feed.Items
for _, item := range items {
c <- item.Title
}
}
当将c <- item.Title替换为fmt.Println(item.Title)时，延迟函数被调用并打印出"DONE"。
英文:
I'm trying to write to a channel as last action in a goroutine function.
Unfortunately this is not working. And the waitGroup is never done.
import (
"sync"
"github.com/SlyMarbo/rss"
"fmt"
)
func main() {
urls := []string{"http://rss.cnn.com/rss/edition.rss", "http://rss.time.com/web/time/rss/top/index.xml"}
var c = make(chan string)
var wg sync.WaitGroup
for _, url := range urls {
wg.Add(1)
go receiveRss(url, &wg, c)
}
wg.Wait()
fmt.Println("==============DONE=================")
}
func receiveRss(url string, wg *sync.WaitGroup, c chan string) {
defer wg.Done()
feed, err := rss.Fetch(url)
if err != nil {
fmt.Println("Failed to retrieve RSS feed", err)
}
items := feed.Items
for _, item := range items {
c <- item.Title
}
}
When replacing c <- item.Title with fmt.Println(item.Title) the deferred function is called and DONE is printed.
答案1
得分: 1
问题是我只是向通道写入数据，从未从中读取数据。
如果不这样做，通道将是无用的。
解决方法是：
在启动goroutine的循环之后从通道中读取数据：
for title := range c {
fmt.Println(title)
}
这会导致无限循环，如果通道从未关闭。
所以我在写入数据后关闭通道：
close(c)
以下是完整的代码：
func main() {
urls := []string{"http://rss.cnn.com/rss/edition.rss", "http://rss.time.com/web/time/rss/top/index.xml"}
var c = make(chan []string)
var wg sync.WaitGroup
for _, url := range urls {
wg.Add(1)
go receiveRss(url, &wg, c)
}
for title := range c {
fmt.Println(title)
}
wg.Wait()
fmt.Println("==============DONE=================")
}
func receiveRss(url string, wg *sync.WaitGroup, c chan []string) {
defer wg.Done()
feed, err := rss.Fetch(url)
if err != nil {
fmt.Println("Failed to retrieve RSS feed", err)
}
items := feed.Items
var titles []string
for _, item := range items {
titles = append(titles, item.Title)
}
c <- titles
close(c)
}
英文:
The problem is that I was only writing to the channel. Never reading from it.
Without doing this the channel would be useless.
The solution to this is:
Reading from the channel after the loop which starts the goroutines:
for title := range c {
fmt.Println(title)
}
This then causes an endless loop if the channel is never closed.
So I just close the channel after writing to it:
close(c)
Here is the whole code:
func main() {
urls := []string{"http://rss.cnn.com/rss/edition.rss", "http://rss.time.com/web/time/rss/top/index.xml"}
var c = make(chan []string)
var wg sync.WaitGroup
for _, url := range urls {
wg.Add(1)
go receiveRss(url, &wg, c)
}
for title := range c {
fmt.Println(title)
}
wg.Wait()
fmt.Println("==============DONE=================")
}
func receiveRss(url string, wg *sync.WaitGroup, c chan []string) {
defer wg.Done()
feed, err := rss.Fetch(url)
if err != nil {
fmt.Println("Failed to retrieve RSS feed", err)
}
items := feed.Items
var titles []string
for _, item := range items {
titles = append(titles, item.Title)
}
c <- titles
close(c)
}
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论