When you have such questions, then run your code with the race detector. https://golang.org/doc/articles/race_detector.html
Otherwise, you are only reading from the slice, there is no racing possible. Also, your max function looks very weird and has a small bug: https://play.golang.org/p/8K-0ze3RdDt The slice calculations has bugs as well, e.g. try running with 64 goroutines. + Egon On Thursday, 19 April 2018 14:35:20 UTC+3, l vic wrote: > > I have a program that calculates max value in integer array by breaking > the array into number of slices and calculating max in every slice inside > of go-routine. > Do I still need to lock/unlock each slice with mutex inside of go-routine? > The code seems to be working but are any apparent problems with it? > > package main > > > import ( > > "fmt" > > "os" > > "strconv" > > "sync" > > ) > > > //returns maximum number found in provided slice > > func maxInSlice(numbers []uint) (uint, error) { > > if numbers == nil { > > return 0, fmt.Errorf("nil numbers") > > } > > > var max uint = 0 > > for _, n := range numbers { > > for _, m := range numbers { > > if n > m { > > max = n > > } > > } > > } > > > return max, nil > > } > > > // finds maximum number in numbers array by breaking work into N > pieces > > // (where N is provided as a command line argument) and processing the > > // pieces in parallel goroutines func main() > > func main() { > > parallelism, _ := strconv.Atoi(os.Args[1]) > > fmt.Printf("ok, i'll use %d goroutines\n", parallelism) > > > numbers := []uint{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13} > > wg := sync.WaitGroup{} > > mutex := sync.Mutex{} > > var allMax uint = 0 > > perGoRoutine := len(numbers) / parallelism > > fmt.Printf("perGoRoutine=%d\n", perGoRoutine) > > > for i := 0; i < parallelism; i++ { > > wg.Add(1) > > go func(i int) { > > defer wg.Done() > > fmt.Printf("==>index i = %d perGoRoutine in go func=%d\n", i, > perGoRoutine) > > startIndex := perGoRoutine * i > > endIndex := startIndex + perGoRoutine - 1 > > //include last element > > if i == parallelism-1 { > > endIndex = len(numbers) - 1 > > > } > > > fmt.Printf("startIndex=%d endIndex=%d\n", startIndex, endIndex) > > sliceMax, err := maxInSlice(numbers[startIndex:endIndex]) > > mutex.Lock() > > if err != nil { > > fmt.Printf("error finding max for slice %d to %d, > skipping this slice: %s\n", err) > > return > > } > > > fmt.Printf("goroutine %d (slice %d to %d) found max > %d\n", i, startIndex, endIndex, sliceMax) > > if sliceMax > allMax { > > allMax = sliceMax > > } > > mutex.Unlock() > > > }(i) > > > } > > wg.Wait() > > > fmt.Printf("maximum: %d\n", allMax) > > > } > > > > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
