golang并发编程示例小记
golang并发编程示例小记
Go提供了sync和channel两种方式来支持协程的并发
0x00 sync
如果我们希望并发下载N个资源,多个并发协程之间不需要通信,那么就可以使用sync.WaitGroup,等待所有并发协程执行结束
package main
import (
"fmt"
"sync"
"time"
)
var wg sync.WaitGroup
func download(url string){
fmt.Println("start downloading:", url)
time.Sleep(time.Second)//模拟耗时
fmt.Println(url + "OK!")
wg.Done()
}
func main(){
for i := 0;i<10;i++{
wg.Add(1)
go download("a.com/" + string(i+'0'))
}
fmt.Println("waiting...")
wg.Wait()
fmt.Println("Done!")
}
//waiting...
//start downloading: a.com/7
//start downloading: a.com/2
//start downloading: a.com/1
//start downloading: a.com/5
//start downloading: a.com/3
//start downloading: a.com/0
//start downloading: a.com/4
//start downloading: a.com/8
//start downloading: a.com/6
//start downloading: a.com/9
//a.com/1OK!
//a.com/0OK!
//a.com/5OK!
//a.com/3OK!
//a.com/7OK!
//a.com/2OK!
//a.com/8OK!
//a.com/6OK!
//a.com/9OK!
//a.com/4OK!
//Done!
- wg.Add(1)表示为wg添加一个计数,wg.Done()减去一个计数
- go download()表示启动新的协程并发执行download函数
- wg.Wait()等待所有协程执行结束
可以看到原来需要10s的并发操作,并发后约1-2s即可执行完毕
0x01 channel
package main
import (
"fmt"
"sync"
"time"
)
var wg sync.WaitGroup
var ch = make(chan string, 10)//创建大小为10的缓冲信道
func download(url string){
fmt.Println("start downloading:", url)
time.Sleep(time.Second)//模拟耗时
fmt.Println(url + " OK!")
ch <- url
}
func main(){
for i := 0;i<10;i++{
go download("a.com/" + string(i+'0'))
}
for i:=0;i<10;i++{
msg:=<-ch//等待信道返回消息
fmt.Println("finish: ", msg)
}
//fmt.Println("waiting...")
//wg.Wait()
fmt.Println("Done!")
}
//start downloading: a.com/9
//start downloading: a.com/2
//start downloading: a.com/5
//start downloading: a.com/7
//start downloading: a.com/0
//start downloading: a.com/8
//start downloading: a.com/6
//start downloading: a.com/1
//start downloading: a.com/3
//start downloading: a.com/4
//a.com/4 OK!
//a.com/5 OK!
//a.com/9 OK!
//a.com/1 OK!
//a.com/7 OK!
//a.com/0 OK!
//a.com/3 OK!
//a.com/6 OK!
//a.com/8 OK!
//finish: a.com/4
//finish: a.com/5
//finish: a.com/9
//finish: a.com/1
//finish: a.com/7
//finish: a.com/0
//finish: a.com/3
//finish: a.com/6
//finish: a.com/8
//a.com/2 OK!
//finish: a.com/2
//Done!
使用channel信道,可以在协程之间传递消息,阻塞等待并发协程返回消息
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