test/chapters/chapter-5/main.go

package main

import (
	"context"
	"fmt"
	"sync"
	"sync/atomic"
	"time"
)

// 5.1 Goroutine 基础
func say(s string) {
	for i := 0; i < 3; i++ {
		time.Sleep(100 * time.Millisecond)
		fmt.Println(s)
	}
}

func goroutineBasic() {
	fmt.Println("=== Goroutine 基础 ===")
	go say("world")
	say("hello")
	time.Sleep(500 * time.Millisecond)
}

// 5.2 GMP 模型演示
func gmpDemo() {
	fmt.Println("\n=== GMP 模型 ===")
	fmt.Printf("GOMAXPROCS: %d\n", runtime.GOMAXPROCS(0))
	fmt.Printf("NumCPU: %d\n", runtime.NumCPU())
	fmt.Printf("NumGoroutine: %d\n", runtime.NumGoroutine())
}

// 5.3 Channel 基础
func channelBasic() {
	fmt.Println("\n=== Channel 基础 ===")
	
	// 无缓冲 Channel
	ch := make(chan int)
	go func() {
		ch <- 42
	}()
	val := <-ch
	fmt.Println("无缓冲 Channel:", val)
	
	// 有缓冲 Channel
	bufferedCh := make(chan int, 2)
	bufferedCh <- 1
	bufferedCh <- 2
	fmt.Println("有缓冲 Channel:", <-bufferedCh, <-bufferedCh)
}

// 5.3 Channel 关闭与遍历
func channelClose() {
	fmt.Println("\n=== Channel 关闭与遍历 ===")
	ch := make(chan int)
	
	go func() {
		for i := 0; i < 5; i++ {
			ch <- i
		}
		close(ch)
	}()
	
	for val := range ch {
		fmt.Print(val, " ")
	}
	fmt.Println()
	
	// 检查关闭
	if _, ok := <-ch; !ok {
		fmt.Println("Channel 已关闭")
	}
}

// 5.3 工作池
func worker(id int, jobs <-chan int, results chan<- int) {
	for j := range jobs {
		fmt.Printf("Worker %d 处理 %d\n", id, j)
		time.Sleep(100 * time.Millisecond)
		results <- j * 2
	}
}

func workerPoolDemo() {
	fmt.Println("\n=== 工作池 ===")
	jobs := make(chan int, 10)
	results := make(chan int, 10)
	
	for w := 1; w <= 3; w++ {
		go worker(w, jobs, results)
	}
	
	for j := 1; j <= 5; j++ {
		jobs <- j
	}
	close(jobs)
	
	for r := 1; r <= 5; r++ {
		<-results
	}
	fmt.Println("工作池完成")
}

// 5.3 Select
func selectDemo() {
	fmt.Println("\n=== Select ===")
	ch1 := make(chan string)
	ch2 := make(chan string)
	
	go func() {
		time.Sleep(500 * time.Millisecond)
		ch1 <- "来自 ch1"
	}()
	
	go func() {
		time.Sleep(300 * time.Millisecond)
		ch2 <- "来自 ch2"
	}()
	
	for i := 0; i < 2; i++ {
		select {
		case msg1 := <-ch1:
			fmt.Println(msg1)
		case msg2 := <-ch2:
			fmt.Println(msg2)
		case <-time.After(1 * time.Second):
			fmt.Println("超时")
			return
		}
	}
}

// 5.4 WaitGroup
func waitGroupDemo() {
	fmt.Println("\n=== WaitGroup ===")
	var wg sync.WaitGroup
	
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			fmt.Printf("Worker %d 开始\n", id)
			time.Sleep(200 * time.Millisecond)
			fmt.Printf("Worker %d 完成\n", id)
		}(i)
	}
	
	wg.Wait()
	fmt.Println("所有任务完成")
}

// 5.4 Mutex
func mutexDemo() {
	fmt.Println("\n=== Mutex ===")
	var mu sync.Mutex
	var count int
	
	for i := 0; i < 1000; i++ {
		go func() {
			mu.Lock()
			count++
			mu.Unlock()
		}()
	}
	
	time.Sleep(1 * time.Second)
	fmt.Println("Count:", count)
}

// 5.4 RWMutex
func rwMutexDemo() {
	fmt.Println("\n=== RWMutex ===")
	var mu sync.RWMutex
	var data = make(map[string]int)
	
	var wg sync.WaitGroup
	
	// 读操作
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			mu.RLock()
			_ = data["key"]
			mu.RUnlock()
		}()
	}
	
	// 写操作
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			mu.Lock()
			data["key"]++
			mu.Unlock()
		}()
	}
	
	wg.Wait()
	fmt.Println("Data:", data)
}

// 5.4 Once
func onceDemo() {
	fmt.Println("\n=== Once ===")
	var once sync.Once
	setup := func() {
		fmt.Println("初始化一次")
	}
	
	for i := 0; i < 5; i++ {
		go func() {
			once.Do(setup)
		}()
	}
	
	time.Sleep(500 * time.Millisecond)
}

// 5.5 Atomic
func atomicDemo() {
	fmt.Println("\n=== Atomic ===")
	var count int64
	
	for i := 0; i < 1000; i++ {
		go func() {
			atomic.AddInt64(&count, 1)
		}()
	}
	
	time.Sleep(1 * time.Second)
	fmt.Println("Atomic Count:", atomic.LoadInt64(&count))
}

// 5.6 Context
func contextDemo() {
	fmt.Println("\n=== Context ===")
	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
	defer cancel()
	
	go func() {
		select {
		case <-time.After(1 * time.Second):
			fmt.Println("任务完成")
		case <-ctx.Done():
			fmt.Println("任务取消:", ctx.Err())
		}
	}()
	
	time.Sleep(1 * time.Second)
}

// 5.8 管道
func pipelineDemo() {
	fmt.Println("\n=== 管道 ===")
	
	// 生成
	gen := func(nums ...int) <-chan int {
		out := make(chan int)
		go func() {
			for _, n := range nums {
				out <- n
			}
			close(out)
		}()
		return out
	}
	
	// 平方
	sq := func(in <-chan int) <-chan int {
		out := make(chan int)
		go func() {
			for n := range in {
				out <- n * n
			}
			close(out)
		}()
		return out
	}
	
	c := gen(1, 2, 3)
	c = sq(c)
	
	for n := range c {
		fmt.Println(n)
	}
}

// 5.9 并发爬虫
type Crawler struct {
	visited map[string]bool
	mu      sync.Mutex
	wg      sync.WaitGroup
	limit   chan struct{}
}

func (c *Crawler) crawl(url string, depth int) {
	if depth <= 0 {
		return
	}
	
	c.limit <- struct{}{}
	defer func() { <-c.limit }()
	defer c.wg.Done()
	
	c.mu.Lock()
	if c.visited[url] {
		c.mu.Unlock()
		return
	}
	c.visited[url] = true
	c.mu.Unlock()
	
	fmt.Println("抓取:", url)
	
	// 模拟子链接
	links := []string{url + "/1", url + "/2"}
	for _, link := range links {
		c.wg.Add(1)
		go c.crawl(link, depth-1)
	}
}

func crawlerDemo() {
	fmt.Println("\n=== 并发爬虫 ===")
	crawler := &Crawler{
		visited: make(map[string]bool),
		limit:   make(chan struct{}, 5),
	}
	
	crawler.wg.Add(1)
	go crawler.crawl("http://example.com", 2)
	
	crawler.wg.Wait()
	fmt.Println("爬虫完成")
}

// 5.10 竞态检测示例（需配合 -race 运行）
func raceDemo() {
	fmt.Println("\n=== 竞态检测示例 ===")
	var count int
	
	for i := 0; i < 100; i++ {
		go func() {
			count++  // 竞态！
		}()
	}
	
	time.Sleep(1 * time.Second)
	fmt.Println("Count:", count)
}

func main() {
	goroutineBasic()
	gmpDemo()
	channelBasic()
	channelClose()
	workerPoolDemo()
	selectDemo()
	waitGroupDemo()
	mutexDemo()
	rwMutexDemo()
	onceDemo()
	atomicDemo()
	contextDemo()
	pipelineDemo()
	crawlerDemo()
	raceDemo()
}