有没有办法知道通道缓冲区中有多少条消息？

Question

I have identified a bottleneck in my program, it is a buffered channel. I would like to give client an indication of system load, which should be indicated by number of messages buffered in the channel.

Is there a way in Go to tell how many buffered messages there are in a channel?

If you also have a Java background, I am looking for an equivelent of this: http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/LinkedBlockingQueue.html#size()

Answer 1

Length and capacity

The built-in functions len and cap take arguments of various types and return a result of type int. The implementation guarantees that the result always fits into an int.

Call      Argument type    Result

len(s)    chan T           number of elements queued in channel buffer

cap(s)    chan T           channel buffer capacity

The len function for a channel gives the number of elements queued in the channel buffer. For example,

package main

import "fmt"

func main() {
    ch := make(chan int, 8)
    ch <- 42
    ch <- 7
    <-ch
    ch <- 64
    // number of queued elements = 1 + 1 - 1 + 1 = 2
    fmt.Println(len(ch), cap(ch))
}

Output:

2 8