example for david with sem + iterator

concurrency/iterator_sem/main.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+func main() {
+
+	generator := func() <-chan int {
+		totalIteration := 30
+		wg := &sync.WaitGroup{}
+		wg.Add(totalIteration)
+		concurrentCount := 20
+		sem := make(chan bool, concurrentCount)
+		defer close(sem)
+		results := make(chan int, totalIteration)
+		defer close(results)
+		for i := 0; i < totalIteration; i++ {
+			sem <- true
+			go func(i int) {
+				results <- generateNumber()
+				<-sem
+				wg.Done()
+			}(i)
+		}
+		wg.Wait()
+		return results
+	}
+
+	results := generator()
+	for r := range results {
+		fmt.Println(r)
+	}
+
+	fmt.Println("Finished!!!")
+}
+
+func generateNumber() int {
+	rand.Seed(time.Now().Unix())
+	time.Sleep(time.Second)
+	return rand.Intn(10000)
+}