通道/ Goroutines抛出错误

Question

I'm currently following this tutorial http://www.miek.nl/files/go/20120807-go.pdf and on chapter 7 it discusses channels/goroutines

However the example code is throwing an error for me just after you run it.

package main

import (
    "fmt"
    "time"
)

var c chan int

func ready(w string, sec int) {
    time.Sleep(time.Duration(sec) * time.Second)
    fmt.Println(w, "is ready!")
    c <- 1
}

func main() {
    c := make(chan int)
    go ready("Tea", 2)
    go ready("Coffee", 1)
    fmt.Println("Waiting...")
    <-c
    <-c
}

Here is the output when you execute the code

daniel:go> go run goroutines.go 
Waiting...
Coffee is ready!
Tea is ready!
throw: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
    /home/daniel/Dropbox/code/go/goroutines.go:21 +0xee

goroutine 2 [syscall]:
created by runtime.main
    /build/buildd/golang-1/src/pkg/runtime/proc.c:221

goroutine 3 [chan send (nil chan)]:
main.ready(0x80bb0d4, 0x3, 0x2, 0x0)
    /home/daniel/Dropbox/code/go/goroutines.go:13 +0xe5
created by main.main
    /home/daniel/Dropbox/code/go/goroutines.go:18 +0x5e

goroutine 4 [chan send (nil chan)]:
main.ready(0x80bba30, 0x6, 0x1, 0x0)
    /home/daniel/Dropbox/code/go/goroutines.go:13 +0xe5
created by main.main
    /home/daniel/Dropbox/code/go/goroutines.go:19 +0x80

goroutine 5 [timer goroutine (idle)]:
created by addtimer
    /build/buildd/golang-1/src/pkg/runtime/ztime_386.c:69
exit status 2

Is there something wrong with my code?

Any help would be appreciated

Answer 1

Yes, just a typo:

package main

import (
    "fmt"
    "time"
)

var c chan int

func ready(w string, sec int) {
    time.Sleep(time.Duration(sec) * time.Second)
    fmt.Println(w, "is ready!")
    c <- 1
}

func main() {
    c = make(chan int) // previously c := make(chan int)
    go ready("Tea", 2)
    go ready("Coffee", 1)
    fmt.Println("Waiting...")
    <-c
    <-c
}

main() didn't use the global c since it declared a new one.

Notice that you don't have to make the channel inside main(), make it while declaring it:

var c = make(chan int)