golang查看channel缓冲区的长度

golang提供内建函数cap用于查看channel缓冲区长度。

cap的定义以下：

func cap(v Type) int 
The cap built-in function returns the capacity of v, according to its type: 
- Array: the number of elements in v (same as len(v)).等同于len

- Pointer to array: the number of elements in *v (same as len(v)).等同于len

- Slice: the maximum length the slice can reach when resliced;
if v is nil, cap(v) is zero.对于slice，表示在不从新分配空间的状况下，能够达到的切片的最大长度。若是切片是nil， 则长度为0.

-  Channel: the channel buffer capacity, in units of elements;表示缓冲区的长度。
if v is nil, cap(v) is zero. 若是通道是nil，则缓冲区长度为0。

Example

package main

import ("fmt")

func main(){

    ch1 := make(chan int)
    ch2 := make(chan int, 2)//缓冲区长度为2

    fmt.Println("ch1 buffer len:", cap(ch1))
    fmt.Println("ch2 buffer len:", cap(ch2))
}

output:

ch1 buffer len:0
ch2 buffer len:2