15. channel

作用

goroutine之间互相通信

无缓冲channel

• make(chan xxx)
• 无缓冲的channel会阻塞，必须等待从channel取出才结束

package main
import "fmt"
func main() {
    // 无缓冲channel
    c:=make(chan int)
    go func() {
        defer fmt.Println("goroutine exit")
        fmt.Println("goroutine running ...")
        // 发送给channel
        c<-0
    }()
    // 读取channel数据
    res:=  <-c
    fmt.Println(res)
    defer fmt.Println("main goroutine exit")
}

goroutine running ...
goroutine exit
0
main goroutine exit

有缓冲channel

• make(chan xxx,size)
• channel满了再次添加会阻塞
• channel空了再次取出会阻塞

package main
import (
    "fmt"
    "time"
)
func main() {
    c := make(chan int,3)
    fmt.Println("init len:",len(c),"cap:",cap(c))
    go func() {
        defer fmt.Println("child goroutine exit")
        for i:=0;i<5;i++ {
            c<-i
            fmt.Println("send:",i,"len:",len(c),"cap:",cap(c))
        }
    }()
    time.Sleep(3*time.Second)
    for i:=0;i<5;i++{
        fmt.Println(<-c)
    }
    defer fmt.Println("main goroutine exit")
}

init len: 0 cap: 3
send: 0 len: 1 cap: 3
send: 1 len: 2 cap: 3
send: 2 len: 3 cap: 3
0
1
2
3
send: 3 len: 3 cap: 3
send: 4 len: 0 cap: 3
child goroutine exit
4
main goroutine exit

关闭channel

• close(xxx)
• 只有不需要发送数据时才需要关闭channel
• 关闭channel后无法再次发送数据
• 关闭channel后可以继续接受数据
• nil channel不可收发

package main
import "fmt"
func main() {
    c:= make(chan int)
    go func() {
        for i:=0;i<3;i++{
            c<-i
        }
        // 当不需要再次发送数据后需要关闭channel,如果被关闭可能会引发死锁
        close(c)
    }()
    for{
        // 如果 channel 没有关闭则 ok 为ture 当channel内没有数据后为false
         if res,ok:= <-c;ok{
             fmt.Println(res)
        }else {
            break
         }
    }
}

0
1
2