go channel learning

I spent several hours to figure out some conceptions about channel tonight

 

1. buffered channel and non-buffered channel

buffered channel

bufferedchan := make(chan int, 1)

when adding element into bufferedchan, it will not blocked if it is not full.

for example:

package main

import "fmt"

func main() {

    messages := make(chan string, 1)

    messages <- "buffered"

    fmt.Println("quit!")
}

the program won't block and the answer is:

quit!

 

2.channel is thread safe, and we can read data from a closed channel

package main

import "fmt"

func main() {
    jobs := make(chan int, 5)
    done := make(chan bool)

    go func() {                           ------------------------------- (Part I)
        fmt.Println("enter go routinue")

        for {
            j, more := <-jobs
            if more {
                fmt.Println("received job", j)
            } else {
                fmt.Println("received all jobs")
                done <- true
                return
            }
        }
    }()

    jobs <- 1                             ------------------------------- (part II)
    jobs <- 2
    jobs <- 3
    close(jobs)
    fmt.Println("sent all jobs and closed")


    <-done                                ------------------------------- (Part III)
}

the result is:

sent all jobs and closed
enter go routinue
received job 1
received job 2
received job 3
received all jobs

 

firstly, it executes (Part II)  and stop at  <-done.

and then a child routinue executes (Part I) and done<-true.

Now the channel done is actived and continue to execute.

 

*If the channel jobs is not closed in main, the statement "j, more := <-jobs" in (Part I) will block.  the deadlock will happen.

*If we don't set "<-done" in main, main will not wait the child routinue to finish.

 

3. range iterates buffered channel seeing https://gobyexample.com/range-over-channels

 

package main

import "fmt"

func main() {

    queue := make(chan string, 2)
    queue <- "one"
    queue <- "two"
    close(queue)

    for elem := range queue {
        fmt.Println(elem)
    }
    fmt.Println("done!")
}

 

if we don't close the queue, it will block in  "elem := range queue".

 

4. a closed channel won't block;  we can't write to it, but we can read from it infinitly. the read value is always 0 value like 0/false/nil

package main

import "fmt"

func main() {

    queue := make(chan int, 2)
    queue <- 10
    queue <- 20
    close(queue)

    for i := 0; i < 10; i++ {
        fmt.Println(<-queue)
    }

    fmt.Println("done!")
}

the result is

10
20
0
0
0
0
0
0
0
0
done!