你可能不知道的关于golang的10件事情

英文原文

匿名结构体

最常见的匿名用法，不用单独定义一个结构体类型

    var config struct {
        APIKey      string
        OAuthConfig oauth.Config
    }

    config.APIKey = "BADC0C0A"

匿名结构体定义时并初始化

    data := struct { Title string Users []*User }{ title, users, }
    err := tmpl.Execute(w, data)

匿名结构体slice定义并初始化

    var indexRuneTests = []struct {
        s    string
        rune rune
        out  int
    }{
        {"a A x", 'A', 2},
        {"some_text=some_value", '=', 9},
        {"☺a", 'a', 3},
        {"a☻☺b", '☺', 4},
    }

嵌套互斥锁

    var hits struct {
        sync.Mutex
        n int
    }

    hits.Lock()
    hits.n++
    hits.Unlock()

嵌套结构体

    type Item struct { Title string URL string }

    type Response struct { Data struct { Children []struct { Data Item }
        }
    }

命令行 go doc

在命令行中，可以通过go doc 查看包相关接口信息

wdy@wdy:~/learn/program-learn/golang$ go doc sync
package sync // import "sync"

Package sync provides basic synchronization primitives such as mutual
exclusion locks. Other than the Once and WaitGroup types, most are intended
for use by low-level library routines. Higher-level synchronization is
better done via channels and communication.

Values containing the types defined in this package should not be copied.

func NewCond(l Locker) *Cond
type Cond struct { ... }
type Locker interface { ... }
type Mutex struct { ... }
type Once struct { ... }
type Pool struct { ... }
type RWMutex struct { ... }
type WaitGroup struct { ... }

wdy@wdy:~/learn/program-learn/golang$ go doc sync Mutex
type Mutex struct {
        // Has unexported fields.
}
    A Mutex is a mutual exclusion lock. Mutexes can be created as part of other
    structures; the zero value for a Mutex is an unlocked mutex.


func (m *Mutex) Lock()
func (m *Mutex) Unlock()

wdy@wdy:~/learn/program-learn/golang$ go doc sync.mutex.lock
func (m *Mutex) Lock()
    Lock locks m. If the lock is already in use, the calling goroutine blocks
    until the mutex is available.

在同一个channel上进行读写操作

battle是一个阻塞channel,当多个goroutine执行warrior的时候，最先执行到select的goroutine进入到

case battle <- name:

此时其他goroutine会阻塞在select上，name进入battle的瞬间，阻塞等待的goroutine的其中一个会进入到

case opponent := <-battle:

battle数据被读取后，阻塞等待的剩余的goroutine的其中一个会进入到

case battle <- name:

按照如上流程反复直到所有goroutine执行完毕。

var battle = make(chan string)

func warrior(name string, done chan struct{}) {
    select {
    case opponent := <-battle:
        fmt.Printf("%s beat %s\n", name, opponent)
    case battle <- name:
        // I lost :-(
    }
    done <- struct{}{}
}

func main() {
    done := make(chan struct{})
    langs := []string{"Go", "C", "C++", "Java", "Perl", "Python"}
    for _, l := range langs {
        go warrior(l, done)
    }
    for _ = range langs {
        <-done
    }
}

可以看到每次结果都是不一样的

wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Go beat Python
C++ beat C
Java beat Perl
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Perl beat Java
Python beat Go
C beat C++
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
C++ beat C
Java beat Perl
Python beat Go
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Go beat Python
Perl beat Java
C beat C++
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Python beat Go
C beat C++
Java beat Perl
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Go beat Python
Perl beat Java
C beat C++
wdy@wdy:~/learn/program-learn/golang$ go run learnchannel.go
Go beat Python
C beat C++
Java beat Perl

利用close来向其他goroutine广播

func waiter(i int, block, done chan struct{}) {
    time.Sleep(time.Duration(rand.Intn(3000)) * time.Millisecond)
    fmt.Println(i, "waiting...")
    <-block
    fmt.Println(i, "done!")
    done <- struct{}{}
}

func main() {
    block, done := make(chan struct{}), make(chan struct{})
    for i := 0; i < 4; i++ {
        go waiter(i, block, done)
    }
    time.Sleep(5 * time.Second)
    close(block)
    for i := 0; i < 4; i++ {
        <-done
    }
}

结果

2 waiting...
1 waiting...
3 waiting...
0 waiting...
0 done!
3 done!
2 done!
1 done!

利用nil通道的特性

goroutine对于值为nil的channel进行接受或发送操作时，会永久block

type Work struct {
    Job string
}

func (w Work) Do() {
    fmt.Println("do", w.Job)
}

func (w Work) Refuse() {
    fmt.Println(w.Job + "stopped")
}

func makeWork(ch chan Work) {
    for {
        time.Sleep(500 * time.Millisecond)
        ch <- Work{Job: "job"}
    }
}

func worker(i int, ch chan Work, quit chan struct{}) {
    for {
        select {
        case w := <-ch:
            if quit == nil {
                w.Refuse()
                fmt.Println("worker", i, "refused", w)
                break
            }
            w.Do()
            fmt.Println("worker", i, "processed", w)
        case <-quit:
            fmt.Println("worker", i, "quitting")
            quit = nil
        }
    }
}

结果

do job
worker 0 processed {job}
do job
worker 1 processed {job}
do job
worker 2 processed {job}
do job
worker 3 processed {job}
do job
worker 0 processed {job}
do job
worker 1 processed {job}
do job
worker 2 processed {job}
do job
worker 3 processed {job}
do job
worker 0 processed {job}
worker 0 quitting
worker 1 quitting
worker 2 quitting
worker 3 quitting
jobstopped
worker 0 refused {job}
jobstopped
worker 1 refused {job}
jobstopped
worker 2 refused {job}
jobstopped
worker 3 refused {job}

后记

之前一直在CSDN上写文章，后面会逐步转换到简书上，还请大家多多支持。