feat: add three patterns

1. generator
2. fan-in
3. fan-out

01-generator/README.md

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+# Generator
+
+
+通常可以拿來做 pipeline 使用，避免一次讀取太大量資料。 其他使用方式還有類似 graceful shutdown 的方法。
+
+參考 [Generator Pattern](./main.go)
+
+補充: 通常產生 channel 人最好要負責關閉 channel，原因有以下兩點
+
+1. 無法向已 closed channel 寫入資料
+2. 可以讀取已 closed channel 的資料

01-generator/main.go

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+package main
+
+import "fmt"
+
+func generateData() <-chan int {
+	data := make(chan int, 1)
+
+	go func(data chan int) {
+		for i := 0; i < 10; i++ {
+			data <- i
+		}
+
+		close(data)
+	}(data)
+
+	return data
+}
+
+func main() {
+	data := generateData()
+
+	for d := range data {
+		fmt.Println(d)
+	}
+}

02-fan-in/README.md

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+# Fan-in
+
+
+通常可以拿來做一些限制流量或是想從多個 output 統一收集 input 使用。
+
+參考 [Fan-In Pattern](./main.go)

02-fan-in/main.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+)
+
+func generateData() <-chan int {
+	data := make(chan int, 1)
+
+	go func(data chan int) {
+		for i := 0; i < 10; i++ {
+			data <- i
+		}
+
+		close(data)
+	}(data)
+
+	return data
+}
+
+func fanIn(sources ...<-chan int) <-chan int {
+	target := make(chan int, 1)
+
+	go func() {
+		defer close(target)
+
+		wg := sync.WaitGroup{}
+
+		for _, source := range sources {
+			wg.Add(1)
+			go func(source <-chan int, target chan int) {
+				defer wg.Done()
+				for val := range source {
+					target <- val
+				}
+			}(source, target)
+		}
+
+		wg.Wait()
+
+	}()
+
+	return target
+}
+
+func main() {
+	data1 := generateData()
+	data2 := generateData()
+	target := fanIn(data1, data2)
+
+	for d := range target {
+		fmt.Println(d)
+	}
+}

03-fan-out/README.md

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+# Fan-out
+
+通常可以拿來當做 Message Queue 使用，從單一 input 散佈到各個地方去。
+
+參考 [Fan-Out Pattern](./main.go)

03-fan-out/main.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func generateData() <-chan int {
+	data := make(chan int, 1)
+
+	go func(data chan int) {
+		for i := 0; i < 10; i++ {
+			data <- i
+		}
+
+		close(data)
+	}(data)
+
+	return data
+}
+
+func fanOut(data <-chan int) <-chan int {
+	target := make(chan int, 1)
+
+	go func(data <-chan int) {
+		defer close(target)
+		for val := range data {
+			target <- val
+		}
+	}(data)
+
+	return target
+}
+
+func main() {
+	data := generateData()
+	target1 := fanOut(data)
+	target2 := fanOut(data)
+
+	go func() {
+		for d := range target1 {
+			fmt.Printf("target1: %d\n", d)
+		}
+	}()
+
+	go func() {
+		for d := range target2 {
+			fmt.Printf("target2: %d\n", d)
+		}
+	}()
+
+	time.Sleep(1 * time.Second) // Easily use time.Sleep to wait them finished instead of sync.WaitGroup
+}

04-fan-in-fan-out/README.md

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+# Fan-In and Fan-Out
+
+把以上兩種做一個整合範例，雖然這範例看起來跟直接讀兩個 channel 很像，但實際上同個 target1 channel 是有可能拿到同樣的值的。
+
+參考 [Fan-In and Fan-Out Pattern](./main.go)

04-fan-in-fan-out/main.go

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+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+func generateData() <-chan int {
+	data := make(chan int, 1)
+
+	go func(data chan int) {
+		for i := 0; i < 10; i++ {
+			data <- i
+		}
+
+		close(data)
+	}(data)
+
+	return data
+}
+
+func fanIn(sources ...<-chan int) <-chan int {
+	target := make(chan int, 1)
+
+	go func() {
+		defer close(target)
+
+		wg := sync.WaitGroup{}
+
+		for _, source := range sources {
+			wg.Add(1)
+			go func(source <-chan int, target chan int) {
+				defer wg.Done()
+				for val := range source {
+					target <- val
+				}
+			}(source, target)
+		}
+
+		wg.Wait()
+
+	}()
+
+	return target
+}
+
+func fanOut(data <-chan int) <-chan int {
+	target := make(chan int, 1)
+
+	go func(data <-chan int) {
+		defer close(target)
+		for val := range data {
+			target <- val
+		}
+	}(data)
+
+	return target
+}
+
+func main() {
+	data1 := generateData()
+	data2 := generateData()
+
+	target := fanIn(data1, data2)
+
+	target1 := fanOut(target)
+	target2 := fanOut(target)
+
+	go func() {
+		for d := range target1 {
+			fmt.Printf("target1: %d\n", d)
+		}
+	}()
+
+	go func() {
+		for d := range target2 {
+			fmt.Printf("target2: %d\n", d)
+		}
+	}()
+
+	time.Sleep(1 * time.Second) // Easily use time.Sleep to wait them finished instead of sync.WaitGroup
+}

README.md

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+# 介紹
+
+此專案是 go concurrency patterns 的各式範例
+
+# 大綱
+
+
+| Number | Name                                      |
+|--------|-------------------------------------------|
+| 1      | [Generator](./01-generator)               | 
+| 2      | [Fan-In](./02-fan-in)                     | 
+| 3      | [Fan-Out](./03-fan-out)                   | 
+| 4      | [Fan-In and Fan-Out](./04-fan-in-fan-out) |