goroutine/channel（1）

channel可以是各種數據類型：

（map類型）

（struct類型）

（接口類型）

package main

import "fmt"

type student struct {
    name string
}

func main() {
    var stuChan chan interface{}
    //空interface類型可以是任意類型
    stuChan = make(chan interface{}, 10)
    stu := student{name:"stu01"}
    stuChan <- &stu

    var stu01 interface{}
    stu01 = <- stuChan

    fmt.Println(stu01)

    var stu02 *student
    //將stu01由interface轉換為結構體類型指針
    stu02, ok := stu01.(*student)
    if !ok {
        fmt.Println("不可以轉換")
        return
    }
    fmt.Println(stu02)

}

輸出：
&{stu01}
&{stu01}

Process finished with exit code 0

channel關閉，判斷：

package main

import "fmt"

func main() {
    var ch chan int
    ch = make(chan int, 10)

    for i := 0; i < 10; i++ {
        ch <- i
    }

    close(ch)

    for {
        var b int
        //從chan取數據的時候第二個參數用來判斷是否成功
        b, ok := <- ch
        if ok == false {
            fmt.Println("chan is closed")
            return
        }
        fmt.Println(b)
    }

}

輸出：
0
1
2
3
4
5
6
7
8
9
chan is closed
range遍歷chan：

package main

import "fmt"

func main() {
    var ch chan int
    ch = make(chan int, 1000)

    for i := 0; i < 1000; i++ {
        ch <- i
    }

    close(ch)
    for v := range ch {
        fmt.Println(v)
    }
}

關閉chan，goroutine同步案例：

package main

import (
    "fmt"
)

func calc(taskChan chan int, resChan chan int,  exitChan chan bool) {
    for v := range taskChan {
        flag := true
        for i := 2; i < v; i++ {
            if v%i == 0 {
                flag = false
                break
            }
        }

        if flag {
            resChan <- v
        }
    }

    fmt.Println("exit")
    //每個calc的協程(goroutine)結束后寫入true到名為exitChan的chan里。代表該goroutine結束了
    exitChan <- true
}

func main() {
    intChan := make(chan int, 1000)
    resultChan := make(chan int, 1000)
    exitChan := make(chan bool, 8)

    go func() {
        for i := 0; i < 10000; i++ {
            intChan <- i
        }

        close(intChan)
    }()

    for i := 0; i < 8; i++ {
        go calc(intChan, resultChan, exitChan)
    }

    //等待所有計算的goroutine全部退出
    go func() {
        for i := 0; i < 8; i++ {
            <-exitChan
            fmt.Println("wait goroute ", i, " exited")
        }
        //8個goroutine結束后關閉resultChan管道
        close(resultChan)
    }()

    //resultChan管道關閉后，range才能在遍歷完后結束
    for v := range resultChan {
        fmt.Println(v)
    }
}

再來個同步channel的例子：

package main

import (
    "fmt"
)

func send(ch chan int, exitChan chan bool) {
    for i := 0; i < 10; i++ {
        ch <- i
    }
    close(ch)
    exitChan <- true
}

func recv(ch chan int, exitChan chan bool) {
    for {
        v, ok := <- ch
        if !ok {
            break
        }
        fmt.Println(v)
    }
    exitChan <- true
}

func main() {
    ch := make(chan int, 10)
    exitChan := make(chan bool, 2)

    go send(ch, exitChan)
    go recv(ch, exitChan)

    var total = 0
    for _ = range exitChan {
        total++
        if total == 2 {
            break
        }
    }

}

輸出：
0
1
2
3
4
5
6
7
8
9

Process finished with exit code 0
channel的只讀，只寫（讀函數里只準讀，寫函數里只準寫。來進行規范，防止出錯）：

package main

import "fmt"

func send(ch chan<- int, exitChan chan struct{}) {

    for i := 0; i < 10; i++ {
        ch <- i
    }

    close(ch)
    var a struct{}
    exitChan <- a
}

func recv(ch <-chan int, exitChan chan struct{}) {
    for {
        v, ok := <-ch
        if !ok {
            break
        }

        fmt.Println(v)
    }

    var a struct{}
    exitChan <- a
}

func main() {
    var ch chan int
    ch = make(chan int, 10)
    exitChan := make(chan struct{}, 2)

    go send(ch, exitChan)
    go recv(ch, exitChan)

    var total = 0
    for _ = range exitChan {
        total++
        if total == 2 {
            break
        }
    }
}