Why this goroutines are asleep?-CodePudding

In my opinion,the "select...case" means "If any chan is available, it executes".So,Why are there error here ,I think message<-msg is available chan send , but it cause deadlock!. thanks very much.


import "fmt"

func main() {
    messages:=make(chan string)
    //signals:=make(chan string)

    select {
    case msg:=<-messages:
        fmt.Println(msg)
    default:
        fmt.Println("no mes receivedd")
    }

    msg:="h1"
    select {
    case messages<-msg:
        fmt.Println("sent message",msg)
    }
}

CodePudding user response：

The first select has a default case, so it selected that immediately. The second select attempts to write to messages, but there are no other goroutines listening, so you have a deadlock.

Move the second select before the first, put it in a goroutine, and remove the default case, then you'll have a successful send/receive.

CodePudding user response：

source geeksforgeeks

Here we have two goroutines map with two functions. one goroutine map with main function and one with an anonymous function.

package main

import (
    "fmt"
)

func main() {
    messages := make(chan string)
    //signals:=make(chan string)
    msg := "h1"
    go func(msg string) {
        select {
        case messages <- msg:
            fmt.Println("sent message", msg)
        }
    }(msg)

    select {
    case msg := <-messages:
        fmt.Println("Message recieved", msg)
    }
}

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