Why is this script hanging on command prompt? - go

Question

I have the following script that generates random sequences and hashes them on the cpu with several threads in go.
package main
import(
"fmt"
"crypto/sha256"
"encoding/hex"
"math/rand"
"time"
"log"
"os"
)
func randChr(i int)(string){
i = i + 65
if i>90 {
i = i - 43
}
return string(i)
}
func randStr(random *rand.Rand, length int)(string){
result := ""
for len(result)<length{
result = result + randChr(random.Intn(36))
}
return result
}
func HashPass(data []byte) (bool,[32]byte){
hash := sha256.Sum256(data)
s := hex.EncodeToString(hash[:])
pass := true
for i := 0; i<7; i++ {
if s[i] != s[i+1]{
pass = false
break;
}
}
return pass,hash
}
func getAPassingHash()(string){
randSource := rand.NewSource(time.Now().UnixNano())
random := rand.New(randSource)
passes := false
s := ""
for !passes {
s=randStr(random,64)
passes,_ = HashPass([]byte(s))
}
return(s)
}
func worker(ch chan string){
ch <- getAPassingHash()
}
func timer(ch chan string,wait time.Duration){
time.Sleep(wait)
ch <- "End"
}
func append(fn string,conts string){
f, err := os.OpenFile(fn,
os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
log.Println(err)
}
defer f.Close()
if _, err := f.WriteString(conts); err != nil {
log.Println(err)
}
}
func main(){
ch := make(chan string)
go timer(ch,6*time.Hour)
for i:=0;i<9;i++{
time.Sleep(time.Second)
go worker(ch)
}
for true{
result := <-ch
if result == "End"{
break;
}
go worker(ch)
fmt.Println(result)
hash := sha256.Sum256([]byte(result))
fmt.Println(hex.EncodeToString(hash[:]))
fmt.Println()
append("hashes.txt","\n"+result+"\n"+hex.EncodeToString(hash[:])+"\n")
}
fmt.Println("done")
}
For some reason the script hangs up occasionally until I click on the command prompt and hit enter. I'm not sure where it is getting stuck but I can see that my system CPU utilization goes down and I know I have results somehow blocking out the program, I hit enter and results print and cpu usage spikes back up. I know this might be hard to replicate but I would really appreciate any suggestions.

Answer 1

It doesn't hang, it waits for the value of passes to be true
func getAPassingHash()(string){
randSource := rand.NewSource(time.Now().UnixNano())
random := rand.New(randSource)
passes := false
s := ""
for !passes { // wait for value is true
s=randStr(random,64)
passes,_ = HashPass([]byte(s))
}
return(s)
}