Validating 9x9 sudoku board using golang and concurrency - go

Question

I am practicing golang by doing coding problems on LeetCode. I am trying to solve a simple sudoku puzzle (it just validates the board). No rows with same digits, no columns with same digits, no 3x3 blocks with same digits. I am trying to use concurrency for learning Go Routines/Channels/Etc...
I can't get the waitgroup to finalize
import (
"sync"
"fmt"
)
func isValidSlice(slice []byte, results chan<- bool, wg *sync.WaitGroup) {
fmt.Println(slice)
seen := make(map[byte]bool)
for _,val := range(slice) {
if seen[val] {
if val != '.'{
results <- false
defer wg.Done()
return
}
} else {
seen[val] = true
}
}
results <- true
defer wg.Done()
}
func isValidSudoku(board [][]byte) bool {
// Channel to receive solution
c := make(chan bool)
// Number of routines that will run (9 for rows, 9 for cols, 9 for 3x3 blocks)
var wg sync.WaitGroup
// Check every row
for x:= 0; x < 9; x++{
wg.Add(1)
go isValidSlice(append([]byte{}, board[x]...), c, &wg)
}
for y:= 0; y < 9; y++{
wg.Add(1)
go isValidSlice(append([]byte{}, board[0:9][y]...), c, &wg)
}
// Check every 3x3 block
for x:= 0; x <= 6; x += 3{
for y := 0; y <= 6; y += 3{
block_digits := append([]byte{}, board[x][y:y+3]...)
block_digits = append(block_digits, board[x+1][y:y+3]...)
block_digits = append(block_digits, board[x+2][y:y+3]...)
wg.Add(1)
go isValidSlice(block_digits, c, &wg)
}
}
fmt.Println("got here")
wg.Wait()
fmt.Println("never got here")
for result := range c{
if !result{
return false
}
}
return true
}
I'm expecting the wg.Wait() lock to release and code to move forward. Then I'm expecting to one of the results in the channel to be false and return false if so. Otherwise, after all elements in the channel are traverse and no false was found, I would expect a True.

Answer 1

Your goroutines cannot call wg.Done() because they all wait to add their value in the channel. But since you only consume the values from the channel after wg.Wait(), all goroutines but one never get to call wg.Done().
You actually don't need a WaitGroup, just remove it.
Other comments:
You should move defer wg.Done() to the first line of isValidSlice. Calling defer on the last line of your function does not make much sense.
You only need a WaitGroup if you want to close the channel properly, you can do that in an additional goroutine, see below for an example on how to do it.
func isValidSudoku(board [][]byte) bool {
// ...
fmt.Println("got here")
go func(){
wg.Wait()
close(c)
}()
fmt.Println("never got here")
for result := range c{
if !result{
go func(){
for _ := range c {
}
}()
return false
}
}
return true
}