duandeng1824
2017-10-27 12:20
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Golang Goroutine添加并发时速度变慢

I am studying about golang and use of goroutine.
With this sample code, on my PC with 4 logical CPUs, I can't understand why I don't have any performance improvement.

If I add in concurrency, the time it takes to do tends to slow down by the original without concurrency.

2017/10/27 13:57:17 Starting 1 threads
2017/10/27 13:57:27 Id routine: 0  rate: 232.558140
2017/10/27 13:57:27 Current total rate was 232.56 K/s
2017/10/27 13:57:27 Starting 1 threads
2017/10/27 13:57:37 Id routine: 0  rate: 357.142857
2017/10/27 13:57:37 Current total rate was 357.14 K/s


2017/10/27 13:58:04 Starting 2 threads
2017/10/27 13:58:14 Id routine: 0  rate: 131.578947
2017/10/27 13:58:14 Id routine: 1  rate: 129.870130
2017/10/27 13:58:14 Current total rate was 261.45 K/s
2017/10/27 13:58:14 Starting 2 threads
2017/10/27 13:58:24 Id routine: 1  rate: 144.927536
2017/10/27 13:58:24 Id routine: 0  rate: 151.515152
2017/10/27 13:58:24 Current total rate was 296.44 K/s

2017/10/27 13:59:15 Starting 3 threads
2017/10/27 13:59:25 Id routine: 2  rate: 94.339623
2017/10/27 13:59:25 Id routine: 0  rate: 92.592593
2017/10/27 13:59:25 Id routine: 1  rate: 90.090090
2017/10/27 13:59:25 Current total rate was 277.02 K/s
2017/10/27 13:59:25 Starting 3 threads
2017/10/27 13:59:35 Id routine: 2  rate: 92.592593
2017/10/27 13:59:35 Id routine: 0  rate: 90.090090
2017/10/27 13:59:35 Id routine: 1  rate: 101.010101
2017/10/27 13:59:35 Current total rate was 283.69 K/s

2017/10/27 14:00:12 Starting 4 threads
2017/10/27 14:00:22 Id routine: 1  rate: 56.818182
2017/10/27 14:00:22 Id routine: 3  rate: 56.818182
2017/10/27 14:00:22 Id routine: 0  rate: 61.349693
2017/10/27 14:00:22 Id routine: 2  rate: 62.500000
2017/10/27 14:00:22 Current total rate was 237.49 K/s
2017/10/27 14:00:22 Starting 4 threads
2017/10/27 14:00:32 Id routine: 1  rate: 67.114094
2017/10/27 14:00:32 Id routine: 3  rate: 61.349693
2017/10/27 14:00:32 Id routine: 0  rate: 57.803468
2017/10/27 14:00:32 Id routine: 2  rate: 65.789474
2017/10/27 14:00:32 Current total rate was 252.06 K/s

And, here is the concurrent code with the goroutines:

package main

import (
    "fmt"
    "log"
    "sync"
    "time"
)

var (
    tryArr           []string
    goroutineQuit    = make(chan struct{})
    concurrencyMapHQ = struct {
        sync.RWMutex
        HQ map[int]float64
    }{HQ: make(map[int]float64)}
)

func rateStats() {
    var totalRate float64
    for i, rate := range concurrencyMapHQ.HQ {
        log.Printf("Id routine: %d  rate: %f", i, rate)
        totalRate += rate
    }

    log.Printf("Current total rate was %.2f K/s", totalRate)
}

func stopThreads(threads int) {
    for i := 0; i < threads; i++ {
        goroutineQuit <- struct{}{}
    }

    rateStats()
}

func runThreads(threads int, steps int) {
    log.Printf("Starting %d threads", threads)

    for i := 0; i < threads; i++ {
        i := i
        go func(id int, steps int) {
            calculate(i, steps)
        }(i, steps)
    }
}

func calculate(idRoutine int, steps int) {
    var (
        possibles []string
        numBatchs = 0
        t1        = time.Now()
    )

    for {
        select {
        case <-goroutineQuit:
            return
        default:
            possibles = nil

            for _, nonce := range tryArr {
                possibles = append(possibles, nonce)
            }

            numBatchs++
            if numBatchs == 99 {
                t2 := time.Now()

                timeExecution := t2.Sub(t1) / time.Millisecond

                concurrencyMapHQ.Lock()
                concurrencyMapHQ.HQ[idRoutine] = float64(steps) / float64(timeExecution)
                concurrencyMapHQ.Unlock()

                numBatchs = 0
                t1 = t2

            }
        }
    }
}

func main() {
    threads := 4
    steps := 10000

    tryArr = make([]string, steps)
    for i := 0; i < steps; i++ {
        tryArr[i] = fmt.Sprintf("indice: %d", i)
    }

    for {
        runThreads(threads, steps)
        time.Sleep(10 * time.Second)
        stopThreads(threads)

        runThreads(threads, steps)
        time.Sleep(10 * time.Second)
        stopThreads(threads)
    }
}
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