Wait groups example added

Author: hamed

15-Concurrency/04-WaitGroups/go.mod

@@ -0,0 +1,3 @@
+module waitGroup
+
+go 1.18

15-Concurrency/04-WaitGroups/main.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+"fmt"
+"io"
+"net/http"
+"strconv"
+"sync"
+)
+
+var TodoList = []string{}
+
+func main() {
+wg := sync.WaitGroup{}
+wg.Add(50) // 50 - 50 = 0
+for i := 0; i < 50; i++ {
+//wg.Add(1)
+go GetTodo(i+1, &wg)
+}
+
+wg.Wait()
+fmt.Printf("%v", TodoList)
+
+}
+
+func GetTodo(id int, wg *sync.WaitGroup) {
+//"https://jsonplaceholder.typicode.com/todos/1"
+GetUrl("https://jsonplaceholder.typicode.com/todos/"+strconv.Itoa(id), wg)
+}
+
+func GetUrl(url string, wg *sync.WaitGroup) {
+defer wg.Done()
+response, err := http.Get(url)
+
+if err != nil {
+panic(err)
+}
+
+responseBody, err := io.ReadAll(response.Body)
+defer response.Body.Close()
+
+if err != nil {
+panic(err)
+}
+
+TodoList = append(TodoList, string(responseBody))
+
+}
+
+// main =>
+// fork task1 task2 task3 task4 task5
+
+//join
+
+// 5
+// -1 => 4
+// -1 => 3
+// ...
+// -1 => 0