golangsync.Cond

package main
import (
"fmt"
"sync"
"time"
)
func main() {
wait := sync.WaitGroup{}
locker := new(sync.Mutex)
cond := sync.NewCond(locker)
for i := 0; i <3; i++ {
go func(i int) {
defer wait.Done()
wait.Add(1)
cond.L.Lock()
fmt.Println("Waiting start...")
cond.Wait()
fmt.Println("Waiting end...")
cond.L.Unlock()
fmt.Println("Goroutine run. Number:", i)
}(i)
}
time.Sleep(2e9)
cond.L.Lock()
cond.Signal()
cond.L.Unlock()
time.Sleep(2e9)
cond.L.Lock()
cond.Signal()
cond.L.Unlock()
time.Sleep(2e9)
cond.L.Lock()
cond.Signal()
cond.L.Unlock()
wait.Wait()
}