✨ (concurrency): add concurrency chapter with goroutines and channels

Author: yuanyu90221

README.md

@@ -83,4 +83,10 @@ copy(stockAmountByRangeClone, stockAmountByRange)
 
 # 參考文件
 
-[slice-intro](https://go.dev/blog/slices-intro)
+[slice-intro](https://go.dev/blog/slices-intro)
+
+# install debug tool
+
+```shell
+go install github.com/go-delve/delve/cmd/dlv@latest
+```

concurrency/REAME.md

@@ -0,0 +1,8 @@
+# concurrency
+
+所謂的併發是指同時間處理多件事情的能力，但不一定是指同時一起進行。也就是可以透過類似 buffer 的方式來接收起來，然後透過一個 worker 逐步執行
+
+## 說明
+
+golang 採用 user level 的執行緒，並且由 goroutine scheduler 來分配執行任務給 os level 的執行序來執行
+

concurrency/concurrency.go

@@ -0,0 +1,28 @@
+package concurrency
+
+type WebsiteChecker func(string) bool
+
+type result struct {
+	string
+	bool
+}
+
+func CheckWebsites(wc WebsiteChecker, urls []string) map[string]bool {
+	results := make(map[string]bool)
+	resultChannel := make(chan result)
+	for _, url := range urls {
+
+		go func() {
+			// results[url] = wc(url)
+			resultChannel <- result{
+				url,
+				wc(url),
+			}
+		}()
+	}
+	for range len(urls) {
+		r := <-resultChannel
+		results[r.string] = r.bool
+	}
+	return results
+}

concurrency/concurrency_test.go

@@ -0,0 +1,44 @@
+package concurrency
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+func mockWebsiteChecker(url string) bool {
+	return url != "waat://furhurerme.geds"
+}
+
+func TestCheckWebsites(t *testing.T) {
+	websites := []string{
+		"http://google.com",
+		"http://blog.gypsydave5.com",
+		"waat://furhurerme.geds",
+	}
+	want := map[string]bool{
+		"http://google.com":          true,
+		"http://blog.gypsydave5.com": true,
+		"waat://furhurerme.geds":     false,
+	}
+
+	got := CheckWebsites(mockWebsiteChecker, websites)
+	if !reflect.DeepEqual(want, got) {
+		t.Fatalf("want %v, got %v", want, got)
+	}
+}
+
+func slowSubWebsiteChecker(_ string) bool {
+	time.Sleep(20 * time.Millisecond)
+	return true
+}
+
+func BenchmarkCheckWebsites(b *testing.B) {
+	urls := make([]string, 100)
+	for i := 0; i < len(urls); i++ {
+		urls[i] = "a url"
+	}
+	for b.Loop() {
+		CheckWebsites(slowSubWebsiteChecker, urls)
+	}
+}