golang基础chan的select操作、定时器操作、超时控制、goroutine中使用recover

chan的只读和只写

a.只读chan的声明
Var 变量的名字 <-chan int
Var readChan <- chan int

b. 只写chan的声明
Var 变量的名字 chan<- int
Var writeChan chan<- int

chan的select操作

格式如下

Select {
case u :&＃61; <- ch1:
case e :&＃61; <- ch2:
default: }


看实例代码&＃xff1a;

package main
import "fmt"
import "time"
func main() {
var ch chan int
ch &＃61; make(chan int ,10)
ch2:&＃61; make(chan int ,10)
go func(){
var i int
for {
ch <- i
time.Sleep(time.Second)
ch2 <- i * i
time.Sleep(time.Second)
i &＃43;&＃43;
}
}()
for {
select{
case v:&＃61; <-ch:
fmt.Println(v)
case v:&＃61; <-ch2:
fmt.Println(v)
default:
fmt.Println("get data timeout")
time.Sleep(time.Second)
}
}
}


输出如下&＃xff1a;

PS E:\golang\go_pro\src\safly> go run demo.go
0
get data timeout
0
get data timeout
1
get data timeout
1
get data timeout
2
get data timeout
4
get data timeout
3
get data timeout
9
get data timeout
4
get data timeout
16
get data timeout
5
get data timeout
exit status 2
PS E:\golang\go_pro\src\safly>

chan的定时器

package main
import "fmt"
import "time"
/* type Ticker struct { C <-chan Time r runtimeTimer } */
func main() {
t :&＃61; time.NewTicker(time.Second)
for v :&＃61; range t.C {
fmt.Println("hello, ", v)
}
}


输出如下&＃xff1a;

PS E:\golang\go_pro\src\safly> go run demo.go
hello, 2017-11-11 18:50:38.165007 &＃43;0800 CST
hello, 2017-11-11 18:50:39.1652525 &＃43;0800 CST
hello, 2017-11-11 18:50:40.165327 &＃43;0800 CST
hello, 2017-11-11 18:50:41.1650873 &＃43;0800 CST
exit status 2
PS E:\golang\go_pro\src\safly>

一次定时器

package main
import "fmt"
import "time"
/* func After(d Duration) <-chan Time { return NewTimer(d).C } */
func main() {
select {
case <- time.After(time.Second):
fmt.Println("after")
}
}


输出如下&＃xff1a;

PS E:\golang\go_pro\src\safly> go run demo.go
after
PS E:\golang\go_pro\src\safly>

超时控制

package main
import "fmt"
import "time"
func queryDb(ch chan int) {
// time.Sleep(time.Second)
ch <- 100
}
func main() {
ch :&＃61; make(chan int)
go queryDb(ch)
t :&＃61; time.NewTicker(time.Second)
select {
case v :&＃61; <-ch:
fmt.Println("result", v)
case <-t.C:
fmt.Println("timeout")
}
}


输出如下&＃xff1a;

PS E:\golang\go_pro\src\safly> go run demo.go
result 100
PS E:\golang\go_pro\src\safly>

以上代码是没有超时的&＃xff0c;我们将上面代码中 // time.Sleep(time.Second)注释去掉
就会输出如下的结果

PS E:\golang\go_pro\src\safly> go run demo.go
timeout
PS E:\golang\go_pro\src\safly>

goroutine中使用recover

应用场景&＃xff0c;如果某个goroutine panic了&＃xff0c;而且这个goroutine里面没有
捕获(recover)&＃xff0c;那么整个进程就会挂掉。所以&＃xff0c;好的习惯是每当go产
生一个goroutine&＃xff0c;就需要写下recover

package main
import (
"fmt"
// "runtime"
"time"
)
func test() {
defer func() {
if err :&＃61; recover(); err !&＃61; nil {
fmt.Println("panic:", err)
}
}()
var m map[string]int
m["stu"] &＃61; 100
}
func calc() {
for {
fmt.Println("i&＃39;m calc")
time.Sleep(time.Second)
}
}
func main() {
go test()
for i :&＃61; 0; i <2; i&＃43;&＃43; {
go calc()
}
time.Sleep(time.Second * 10000)
}


输出如下&＃xff1a;

PS E:\golang\go_pro\src\safly> go run demo.go
i&＃39;m calc
panic: assignment to entry in nil map
i&＃39;m calc
i&＃39;m calc
i&＃39;m calc
i&＃39;m calc
i&＃39;m calc
i&＃39;m calc
i&＃39;m calc
exit status 2
PS E:\golang\go_pro\src\safly>