package main
import (
"fmt"
"os"
"os/exec"
"bufio"
"reflect"
)
func runTheCommand(ch chan<- string, cmD string) {
ouT,_ := exec.Command("sh","-c",cmD).Output()
ch <- string(ouT)
}
// Readln returns a single line (without the ending
) from the input buffered reader. An error is returned iff there is an error with the buffered reader.
func Readln(r *bufio.Reader) (string, error) {
var (isPrefix bool = true
err error = nil
line, ln []byte
)
for isPrefix && err == nil {
line, isPrefix, err = r.ReadLine()
ln = append(ln, line...)
}
return string(ln),err
}
func main() {
var chans = []chan string{}
f, _ := os.Open("../tmpStatus.config")
r := bufio.NewReader(f)
cmD, e := Readln(r)
for e == nil {
ch := make(chan string)
chans = append(chans, ch)
go runTheCommand(ch,cmD)
cmD,e = Readln(r)
}
cases := make([]reflect.SelectCase, len(chans))
for i, ch := range chans {
cases[i] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(ch)}
}
remaining := len(cases)
for remaining > 0 {
chosen, value, ok := reflect.Select(cases)
if !ok {
cases[chosen].Chan = reflect.ValueOf(nil)
remaining -= 1
continue
}
fmt.Printf("%s", value.String())
}
}
This code is correctly printing out all the received values from the channels. But in the end it is exiting with the below error :
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [select]: reflect.rselect(0xc200283480, 0x22, 0x22, 0xffffffffffffffff, 0x0, ...) /usr/local/go/src/pkg/runtime/chan.c:1212 +0x10d reflect.Select(0xc200066800, 0x22, 0x22, 0x1, 0x0, ...) /usr/local/go/src/pkg/reflect/value.go:1957 +0x1fb
I am a newbee at GO. I referred google and somehow managed to write a working code. I didn't understand fully how this script works especially the reflect package commands. My intention here is to execute the unix commands listed in ../tmpStatus.config file parallely and print out the results. I am excited by the concurrency features offered by GO and hence decided to give it a try. Now it is printing the results so fast. Till now, I was doing this in python one by one. I ran this script in go version go1.1.2 linux/amd64 installed to a custom location. Any idea why the deadlock is happening ?
