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)
}
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