WaitGroup 主要用于控制任务组下的并发子任务。它的具体做法就是，子任务 goroutine 执行前通过 Add 方法添加任务数目，子任务 goroutine 结束时调用 Done 标记已完成任务数，主任务 goroutine 通过 Wait 方法等待所有的任务完成后才能执行后续逻辑
package main
import (
"net/http"
"sync"
)
func main() {
var wg sync.WaitGroup
var urls = []string{
"http://www.golang.org/",
"http://www.baidu.com/",
"http://www.bokeyuan12111.com/",
}
for _, url := range urls {
wg.Add(1)
go func(url string) {
defer wg.Done()
resp, err := http.Get(url)
if err != nil {
return
}
resp.Body.Close()
}(url)
}
wg.Wait()
}
但在实际的项目代码中，子任务 goroutine 的执行并不总是顺风顺水，它们也许会产生 error。而 WaitGroup 并没有告诉我们在子 goroutine 发生错误时，如何将其抛给主任务 groutine。这个时候可以考虑使用 errgroup
package main
import (
"fmt"
"net/http"
"golang.org/x/sync/errgroup"
)
func main() {
var urls = []string{
"http://www.golang.org/",
"http://www.baidu.com/",
"http://www.bokeyuan12111.com/",
}
g := new(errgroup.Group)
for _, url := range urls {
url := url
g.Go(func() error {
resp, err := http.Get(url)
if err != nil {
fmt.Println(err)
return err
}
fmt.Printf("get [%s] success: [%d] \n", url, resp.StatusCode)
return resp.Body.Close()
})
}
if err := g.Wait(); err != nil {
fmt.Println(err)
} else {
fmt.Println("All success!")
}
}
get [http://www.baidu.com/] success: [200]
Get "http://www.bokeyuan12111.com/": dial tcp: lookup www.bokeyuan12111.com: no such host
Get "http://www.golang.org/": dial tcp 142.251.42.241:80: i/o timeout
Get "http://www.bokeyuan12111.com/": dial tcp: lookup www.bokeyuan12111.com: no such host
errgroup 上下文取消
package main
import (
"context"
"fmt"
"golang.org/x/sync/errgroup"
)
func main() {
g, ctx := errgroup.WithContext(context.Background())
dataChan := make(chan int, 20)
// 数据生产端任务子 goroutine
g.Go(func() error {
defer close(dataChan)
for i := 1; ; i++ {
if i == 10 {
return fmt.Errorf("data 10 is wrong")
}
dataChan <- i
fmt.Println(fmt.Sprintf("sending %d", i))
}
})
// 数据消费端任务子 goroutine
for i := 0; i < 3; i++ {
g.Go(func() error {
for j := 1; ; j++ {
select {
case <-ctx.Done():
return ctx.Err()
case number := <-dataChan:
fmt.Println(fmt.Sprintf("receiving %d", number))
}
}
})
}
// 主任务 goroutine 等待 pipeline 结束数据流
err := g.Wait()
if err != nil {
fmt.Println(err)
}
fmt.Println("main goroutine done!")
}
sending 1
sending 2
sending 3
sending 4
sending 5
sending 6
sending 7
sending 8
sending 9
receiving 1
receiving 3
receiving 2
receiving 4
data 10 is wrong
main goroutine done!