package main

import (
    "fmt"
    "math/rand"
    "runtime"
    "sync"
)

const NB_WORKERS = 3000
const JOB_COUNTING_TO = 10000000

var mu sync.Mutex
var guard chan struct{}
var nbConcurrentGoRoutines = 0
var jobsDone = 0

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

func doJob(job int) {
    nbConcurrentGoRoutines = max(nbConcurrentGoRoutines, runtime.NumGoroutine())

    if rand.Intn(10) == 0 {
        return
    }

    for i := 0; i < job; i += 1 {
    }

    mu.Lock()
    jobsDone += 1
    mu.Unlock()

    var wg sync.WaitGroup
    for i := 0; i < 18; i += 1 {
        guard <- struct{}{}
        wg.Add(1)
        go func() {
            doJob(JOB_COUNTING_TO)
            wg.Done()
        }()
    }
    wg.Wait()
    <-guard
}

func main() {
    guard = make(chan struct{}, NB_WORKERS)
    doJob(JOB_COUNTING_TO)
    fmt.Println(jobsDone, nbConcurrentGoRoutines)
}