howood/imagereductor

package utils

import (
    "runtime"
    "sync"
)

var numParallelInstance = runtime.NumCPU() * 5

// ApplyParallel is apply each funcs parallelly
func ApplyParallel(start, end int, fnc func(start, end int)) {
    chunks := divideToChunk(start, end)
    var wg sync.WaitGroup
    for _, chunk := range chunks {
        wg.Add(1)
        funcChunk := chunk
        go func() {
            defer wg.Done()
            fnc(funcChunk["start"], funcChunk["end"])
        }()
    }
    wg.Wait()
}

func divideToChunk(start, end int) []map[string]int {
    chunks := make([]map[string]int, 0)
    allCount := end - start
    dividePoint := allCount / numParallelInstance
    if dividePoint < 1 {
        dividePoint = allCount
    }
    countStart := start
    countEnd := dividePoint
    for countStart < end {
        chunk := make(map[string]int, 0)
        chunk["start"] = countStart
        chunk["end"] = countEnd
        chunks = append(chunks, chunk)
        countStart += dividePoint
        countEnd += dividePoint
        if countEnd > end {
            countEnd = end
        }
    }
    return chunks
}