Go语言基础

Posted 2022-08-10 想考北航的小刺猬

Concurrency

Goroutines

goroutine是一个轻量级的线程通过Go runtime（运行时）管理

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")

Channels

Channel是一种有类型的管道，通过它，可以用运算符<-发送和接收数据。

ch <- v    // Send v to channel ch.
v := <-ch  // Receive from ch, and
           // assign value to v.

channel必须在用之前先创建：

ch := make(chan int)

默认情况下，发送和接收阻塞，直到另一方准备好。这允许goroutines同步，而不需要显式的锁或条件变量。

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 := []int7, 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)

Buffer Channels

可以给通道一个长度。

ch := make(chan int, 100)

Range and Close

发送方可以关闭通道，以表示不再发送任何值。接收器可以通过给receive表达式赋值第二个参数来测试通道是否已经关闭

v, ok := <-ch

根据OK的值来判断是否关闭，之应该允许sender关闭通道而不允许receiver关闭。channel不像文件，通常不需要关闭，只有当接收者再也不接收数据了，就可以关闭了。

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)
	

Select

select语句允许goroutine等待多个通信操作。select会阻塞直到其中一个用例能运行，然后执行这个用例，多个用例准备好则随机选一个。

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)

• default case:如果没有用例准备好，就运行default case

sync.Mutex

信号量，互斥锁

• Lock
• Unlock

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 := SafeCounterv: make(map[string]int)
	for i := 0; i < 1000; i++ 
		go c.Inc("somekey")
	

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