channe状态与读取操作之间的关系

╰+哭是因爲堅強的太久メ 2022-01-10 16:49 165阅读 0赞

### channe状态与读取操作之间的关系 ###

本文主要记录通道不同状态下，读取和写入通道结果之间的关系。  
整体上以记录表格形式呈现，后边每一个test()方法表示了一种情况。

<table> 
 <thead> 
  <tr> 
   <th>操作</th> 
   <th>Channel状态</th> 
   <th>结果</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Read</td> 
   <td>未初始化</td> 
   <td>阻塞</td> 
  </tr> 
  <tr> 
   <td>Read</td> 
   <td>已初始化且非空有值</td> 
   <td>读取到正确值</td> 
  </tr> 
  <tr> 
   <td>Read</td> 
   <td>已初始化但为空</td> 
   <td>所在协程阻塞</td> 
  </tr> 
  <tr> 
   <td>Read</td> 
   <td>关闭状态的</td> 
   <td>读取到默认值</td> 
  </tr> 
  <tr> 
   <td>Read</td> 
   <td>通道为只写</td> 
   <td>编译错误</td> 
  </tr> 
  <tr> 
   <td>Write</td> 
   <td>未初始化</td> 
   <td>所在协程阻塞</td> 
  </tr> 
  <tr> 
   <td>Write</td> 
   <td>已初始化且缓冲未满</td> 
   <td>值可以被正确写入</td> 
  </tr> 
  <tr> 
   <td>Write</td> 
   <td>已初始化但缓冲已满</td> 
   <td>此协程阻塞，直到有值被取走</td> 
  </tr> 
  <tr> 
   <td>write</td> 
   <td>通道为只读</td> 
   <td>编译错误</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>未初始化的channel</td> 
   <td>会引发panic</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>已初始化且缓冲有值</td> 
   <td>通道关闭，并读取到值，最后读取到默认零值</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>已初始化且缓冲无值的channel</td> 
   <td>通道关闭并读取到默认值</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>关闭一个已经关闭的channel</td> 
   <td>会引发panic</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>关闭一个只读的channel</td> 
   <td>会引发panic</td> 
  </tr> 
  <tr> 
   <td>Close</td> 
   <td>关闭一个只写的channel</td> 
   <td>通道会正常关闭</td> 
  </tr> 
 </tbody> 
</table>

package main
    
    import (
    	"fmt"
    )
    
    func main() {
    
    	test1()  // 1. 读取一个未初始化的channel---->此协程永久阻塞
    	test2()  // 2. 读取一个初始化并非空的channel---->正确读到值
    	test3()  // 3. 读取一个初始化但为空的channel---->此协程永久阻塞
    	test4()  // 4. 读取一个关闭的channel---->默认值，false
    	test5()  // 5. 读取一个只写类型的channel---->编译错误
    	test6()  // 6. 写入一个未初始化的channel---->此协程永久阻塞
    	test7()  // 7. 写入一个初始化且满缓冲的channel---->此协程阻塞，直到有值被取走
    	test8()  // 8. 写入一个初始化且缓冲未满的channel---->值可以正常写入
    	test9()  // 9. 写入一个关闭的channel---->会引发panic
    	test10() // 10. 写入一个只读channel---->编译错误
    	test11() // 11. 关闭一个未初始化的channel---->会引发panic
    	test12() // 12. 关闭一个初始化且缓冲有值的channel---->通道关闭，且读取到缓冲中的值，直到无值了才读取到默认值
    	test13() // 13. 关闭一个初始化且缓冲无值的channel---->通道关闭，读取到的值为默认值。
    	test14() // 14. 关闭一个已经关闭了的channle---->会引发panic
    	test15() // 15. 关闭一个只读的channel---->会引发panic
    	test16() // 16. 关闭一个只写的channel---->正常关闭
    
    }
    
    // 1. 读取一个未初始化的channel---->此协程永久阻塞
    func test1() {
    	var streamChannel chan int
    	fmt.Println("streamChannel is ", streamChannel)
    	fmt.Printf("read channel: %v", <-streamChannel)
    
    	/*
    
    	streamChannel is  <nil>
    	fatal error: all goroutines are asleep - deadlock!
    
    	*/
    }
    
    // 2. 读取一个初始化并非空的channel---->正确读到值
    func test2() {
    	var streamChannel = make(chan int, 1)
    	fmt.Println("streamChannel is ", streamChannel)
    	streamChannel <- 2
    	fmt.Printf("read channel: %v", <-streamChannel)
    
    	/*
    
    	streamChannel is  0xc000034070
    	read channel: 2
    
    	*/
    }
    
    // 3. 读取一个初始化但为空的channel---->此协程永久阻塞
    func test3() {
    	var streamChannel = make(chan int, 1)
    	fmt.Println("streamChannel is ", streamChannel)
    	fmt.Printf("read channel: %v", <-streamChannel)
    	/*
    
    	streamChannel is  0xc000082000
    	fatal error: all goroutines are asleep - deadlock!
    
    	*/
    
    }
    
    // 4. 读取一个关闭的channel---->默认值，false
    func test4() {
    	var streamChannel = make(chan int, 1)
    	close(streamChannel)
    	select {
    	case value, ok := <-streamChannel:
    		fmt.Printf("value:%v  ,  ok: %v", value, ok)
    	}
    
    	/*
    
    	value:0  ,  ok: false
    
    	*/
    
    }
    
    // 5. 读取一个只写类型的channel---->编译错误
    func test5() {
    	//var streamChannel = make(chan <-int,1)
    	//var value = <- streamChannel		//直接爆红编译错误
    	/*
    
    	invalid operation: <-streamChannel (receive from send-only type chan<- int)
    
    	*/
    }
    
    // 6. 写入一个未初始化的channel---->此协程永久阻塞
    func test6() {
    	var streamChannel chan int
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	streamChannel <- 6
    	fmt.Printf("write the end!")
    	/*
    
    	streamChannel is <nil> 
    	fatal error: all goroutines are asleep - deadlock!
    
    	*/
    }
    
    // 7. 写入一个初始化且满缓冲的channel---->此协程阻塞，直到有值被取走
    func test7() {
    	var streamChannel = make(chan int, 2)
    	fmt.Printf("streamChannel:%v\n", streamChannel)
    	streamChannel <- 7
    	streamChannel <- 77
    	streamChannel <- 777
    
    	/*
    
    	fatal error: all goroutines are asleep - deadlock!
    	streamChannel:0xc000082000
    		
    	*/
    }
    
    // 8. 写入一个初始化且缓冲未满的channel---->值可以正常写入
    func test8() {
    	var streamChannel = make(chan int, 3)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	streamChannel <- 8
    	streamChannel <- 88
    	fmt.Printf("write the end!")
    	/*
    
    	streamChannel is 0xc000082000
    	write the end!
    	
    	*/
    }
    
    // 9. 写入一个关闭的channel---->会引发panic
    func test9() {
    	var streamChannel = make(chan int, 1)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	close(streamChannel)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	streamChannel <- 9
    	fmt.Printf("write the end!")
    
    	/*
    
    	streamChannel is 0xc000082000
    	streamChannel is 0xc000082000
    	panic: send on closed channel
    
    	*/
    
    }
    
    // 10. 写入一个只读channel---->编译错误
    func test10() {
    
    	//var streamChannel = make(<- chan int,1)
    	//fmt.Printf("streamChannel is %v",streamChannel)
    	//streamChannel <- 10
    	//fmt.Printf("write the end!")
    	/*
    
    	invalid operation: streamChannel <- 10 (send to receive-only type <-chan int)
    
    	*/
    }
    
    // 11. 关闭一个未初始化的channel---->会引发panic
    func test11() {
    	var streamChannel chan int
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	close(streamChannel)
    	fmt.Printf("the end!")
    
    	/*
    
    	streamChannel is <nil>
    	panic: close of nil channel
    
    	*/
    }
    
    // 12. 关闭一个初始化且缓冲有值的channel---->通道关闭，且读取到缓冲中的值，直到无值了才读取到默认值
    func test12() {
    	var streamChannel = make(chan int, 2)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	streamChannel <- 12
    	streamChannel <- 1212
    	close(streamChannel)
    	fmt.Printf("第一次读取值：%v\n", <-streamChannel)
    	fmt.Printf("第二次读取值：%v\n", <-streamChannel)
    	fmt.Printf("第三次读取值：%v\n", <-streamChannel) // 前两次读完之后，通道里面没有值了，再次读取时，就是默认值了
    	fmt.Printf("read the end!")
    
    	/*
    
    	streamChannel is 0xc000082000
    	第一次读取值：12
    	第二次读取值：1212
    	第三次读取值：0
    	read the end!
    
    	*/
    }
    
    // 13. 关闭一个初始化且缓冲无值的channel---->通道关闭，读取到的值为默认值。
    func test13() {
    	var streamChannel = make(chan int, 2)
    	close(streamChannel)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	fmt.Printf("第一次读取通道里的值：%v\n", <-streamChannel)
    	fmt.Printf("第二次读取通道里的值：%v\n", <-streamChannel)
    	fmt.Printf("第三次读取通道里的值：%v\n", <-streamChannel) // 无论读多少次，读到的都是默认值
    
    	/*
    
    	streamChannel is 0xc000034070
    	第一次读取通道里的值：0
    	第二次读取通道里的值：0
    	第三次读取通道里的值：0
    
    	*/
    
    }
    
    // 14. 关闭一个已经关闭了的channle---->会引发panic
    func test14() {
    	var streamChannel = make(chan int, 1)
    	fmt.Printf("1. streamChannel is %v\n", streamChannel)
    	close(streamChannel)
    	fmt.Printf("2. streamChannel is %v\n", streamChannel)
    	close(streamChannel)
    	fmt.Printf("3. streamChannel is %v\n", streamChannel) // 可以看到"关闭一个已经关闭了的channel会引发panic"
    
    	/*
    
    	1. streamChannel is 0xc000034070
    	2. streamChannel is 0xc000034070
        panic: close of closed channel
    
    	*/
    
    }
    
    // 15. 关闭一个只读的channel---->会引发panic
    func test15() {
    	//var streamChannel = make(<-chan int, 1)
    	//fmt.Printf("streamChannel is %v\n", streamChannel)
    	//close(streamChannel)// 直接爆红，不允许编译
    }
    
    // 16. 关闭一个只写的channel---->正常关闭
    func test16() {
    	var streamChannel = make(chan<- int, 1)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	close(streamChannel)
    	fmt.Printf("streamChannel is %v\n", streamChannel)
    	/*
    
    	streamChannel is 0xc000034070
    	streamChannel is 0xc000034070
    
    	*/
    }