sync.go

package main

import (
	"fmt"
	"time"
)

func main() {
	ch := make(chan int)
	for i := 0; i < 100; i++ {
		go func(i int) {
			fmt.Println(i, <-ch)
		}(i)
	}
	time.Sleep(1000)
	go func() {
		ch <- 1
	}()

	go func() {
		ch <- 2
	}()
	time.Sleep(1000)
}

Решението ти за синхронизация със sleep е доста непостоянно. Разгледай този пример:

package main

import (
    "fmt"
    "sync"
)

func main() {
    ch := make(chan int)
    start := make(chan struct{})
    var wg sync.WaitGroup

    for i := 0; i < 100; i++ {
        wg.Add(1)
        go func(i int) {
            defer wg.Done()
            <-start
            fmt.Println(i, <-ch)
        }(i)
    }   
    close(start)
    for i := 0; i < 100; i++ {
        ch <- i
    }   

    wg.Wait()
}