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go f(x, y, z)

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f(x, y, z)

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package main

import (
	"fmt"
	"time"
)

func say(s string) {
	for i := 0; i < 5; i++ {
		time.Sleep(100 * time.Millisecond)
		fmt.Println(s)
	}
}

func main() {
	go say("world")
	say("hello")
}

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ch <- v    // Send v to channel ch. => 将 v 发送至通道 ch。
v := <-ch  // Receive from ch, and assign value to v. => 从 ch 接收值并赋予 v。

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ch := make(chan int)

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package main

import "fmt"

func sum(s []int, c chan int) {
	sum := 0
	for _, v := range s {
		sum += v
	}
	c <- sum // send sum to c
}

func main() {
	s := []int{7, 2, 8, -9, 4, 0}

	c := make(chan int)
	go sum(s[:len(s)/2], c)
	go sum(s[len(s)/2:], c)
	x, y := <-c, <-c // receive from c

	fmt.Println(x, y, x+y)
}

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ch := make(chan int, 100)

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package main

import "fmt"

func main() {
	ch := make(chan int, 2)
	ch <- 1
	ch <- 2
    // ch <- 3 // fatal error: all goroutines are asleep - deadlock!
	fmt.Println(<-ch)
	fmt.Println(<-ch)
}

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v, ok := <-ch

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package main

import (
	"fmt"
)

func fibonacci(n int, c chan int) {
	x, y := 0, 1
	for i := 0; i < n; i++ {
		c <- x
		x, y = y, x+y
	}
	close(c)
}

func main() {
	c := make(chan int, 10)
	go fibonacci(cap(c), c)
	for i := range c {
		fmt.Println(i)
	}
}

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package main

import "fmt"

func fibonacci(c, quit chan int) {
	x, y := 0, 1
	for {
		select {
		case c <- x:
			x, y = y, x+y
		case <-quit:
			fmt.Println("quit")
			return
		}
	}
}

func main() {
	c := make(chan int)
	quit := make(chan int)
	go func() {
		for i := 0; i < 10; i++ {
			fmt.Println(<-c)
		}
		quit <- 0
	}()
	fibonacci(c, quit)
}

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select {
case i := <-c:
    // use i
default:
    // receiving from c would block => 从 c 中接收会阻塞时执行
}

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package main

import (
	"fmt"
	"time"
)

func main() {
	tick := time.Tick(100 * time.Millisecond)
	boom := time.After(500 * time.Millisecond)
	for {
		select {
		case <-tick:
			fmt.Println("tick.")
		case <-boom:
			fmt.Println("BOOM!")
			return
		default:
			fmt.Println("    .")
			time.Sleep(50 * time.Millisecond)
		}
	}
}

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type Tree struct {
    Left  *Tree
    Value int
    Right *Tree
}

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go Walk(tree.New(1), ch)

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package main

import (
	"fmt"
	"golang.org/x/tour/tree"
)

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
    if t.Left != nil {
		Walk(t.Left, ch)
	}
	ch <- t.Value
	if t.Right != nil {
		Walk(t.Right, ch)
	}
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
    var v1, v2 int
	c1 := make(chan int)
	c2 := make(chan int)
	go Walk(t1, c1)
	go Walk(t2, c2)
	for i := 0; i < 10; i++ {
		v1 = <-c1
		v2 = <-c2
		if v1 != v2 {
			return false
		}
	}
	return true
}

func main() {
    ch := make(chan int)
	go Walk(tree.New(10), ch)
	for i := 0; i < 10; i++ {
		fmt.Println(<-ch)
	}
	fmt.Println(Same(tree.New(1), tree.New(1)))
}

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package main

import (
	"fmt"
	"sync"
	"time"
)

// SafeCounter is safe to use concurrently.
type SafeCounter struct {
	mu sync.Mutex
	v  map[string]int
}

// Inc increments the counter for the given key.
func (c *SafeCounter) Inc(key string) {
	c.mu.Lock()
	// Lock so only one goroutine at a time can access the map c.v.
	c.v[key]++
	c.mu.Unlock()
}

// Value returns the current value of the counter for the given key.
func (c *SafeCounter) Value(key string) int {
	c.mu.Lock()
	// Lock so only one goroutine at a time can access the map c.v.
	defer c.mu.Unlock()
	return c.v[key]
}

func main() {
	c := SafeCounter{v: make(map[string]int)}
	for i := 0; i < 1000; i++ {
		go c.Inc("somekey")
	}

	time.Sleep(time.Second)
	fmt.Println(c.Value("somekey"))
}

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package main

import (
	"fmt"
	"sync"
)

type Fetcher interface {
	// Fetch returns the body of URL and
	// a slice of URLs found on that page.
	Fetch(url string) (body string, urls []string, err error)
}

type UrlChecker struct {
	urls map[string]bool
	mux sync.Mutex
}

func (c *UrlChecker) Crawled(url string) bool {
	c.mux.Lock()
	if c.urls[url] {
		defer c.mux.Unlock()
		return true
	}
	c.urls[url] = true
	defer c.mux.Unlock()
	return false
}

var uc = UrlChecker{urls: make(map[string]bool)}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, ret chan string) {
	// TODO: Fetch URLs in parallel.
	// TODO: Don't fetch the same URL twice.
	// This implementation doesn't do either:
	defer close(ret)
	if depth <= 0 {
		return
	}
	if uc.Crawled(url) {
		return
	}
	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		fmt.Println(err)
		return
	}
	ret <- fmt.Sprintf("found: %s %q\n", url, body)
	results := make([]chan string, len(urls))
	for i, u := range urls {
		results[i] = make(chan string)
		go Crawl(u, depth-1, fetcher, results[i])
	}
	
	for _, result := range results {
		for s := range result {
			ret <- s
		}
	}
	
	return
}

func main() {
	result := make(chan string)
	go Crawl("https://golang.org/", 4, fetcher, result)
	for s := range result {
		fmt.Println(s)
	}
}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
	body string
	urls []string
}

func (f fakeFetcher) Fetch(url string) (string, []string, error) {
	if res, ok := f[url]; ok {
		return res.body, res.urls, nil
	}
	return "", nil, fmt.Errorf("not found: %s", url)
}

// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
	"https://golang.org/": &fakeResult{
		"The Go Programming Language",
		[]string{
			"https://golang.org/pkg/",
			"https://golang.org/cmd/",
		},
	},
	"https://golang.org/pkg/": &fakeResult{
		"Packages",
		[]string{
			"https://golang.org/",
			"https://golang.org/cmd/",
			"https://golang.org/pkg/fmt/",
			"https://golang.org/pkg/os/",
		},
	},
	"https://golang.org/pkg/fmt/": &fakeResult{
		"Package fmt",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
	"https://golang.org/pkg/os/": &fakeResult{
		"Package os",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
}