监控golang中的频道充值

Question

There are several channels to monitor, their type are different and irrelevant(since we only care about len and cap), but golang compiler does not accept following code, whatever T is:

func monitorChan(ch chan T) {
    for {
        if len(ch) == cap(ch) {
            log.Warn("log")
        }
        time.Sleep(chanMonitorInterval)
    }
}

it shows error:

cannot use ch (type chan []byte) as type chan interface {} in argument to monitorChan.

How can this function be modified to write once monitor every channel?

---

Here is my code:

package main

import (
    "fmt"
    "time"
)

func monitorChan(ch chan interface{}) {
    for {
        if len(ch) == cap(ch) {
            fmt.Println("log")
        }
        time.Sleep(1 * time.Second)
    }
}

func main() {
    ch := make(chan []byte, 100)
    go monitorChan(ch)
    // actual things below ...
}

Playground: https://play.golang.org/p/t7T28IpLNAs

Answer 1

Use reflection. For example,

package main

import (
    "log"
    "reflect"
    "time"
)

func monitorChan(ch interface{}, intvl time.Duration) {
    v := reflect.ValueOf(ch)
    if v.Kind() != reflect.Chan {
        return
    }

    c := v.Cap()
    if c == 0 {
        return
    }
    for {
        if l := v.Len(); l == c {
            log.Printf("log: len(%d) cap(%d)", l, c)
        }
        time.Sleep(intvl)
    }
}

func main() {
    log.Print("main")
    c := make(chan []byte, 10)
    var chanMonitorInterval = 1 * time.Second
    go monitorChan(c, chanMonitorInterval)
    log.Print("monitor")

    time.Sleep(5 * chanMonitorInterval)
    for len(c) != cap(c) {
        c <- []byte{}
    }
    log.Print("len(c) == cap(c)")
    time.Sleep(3 * chanMonitorInterval)
    <-c
    log.Print("len(c) < cap(c)")
    time.Sleep(5 * chanMonitorInterval)
    log.Print("main")
}

Playground: https://play.golang.org/p/c5VhIIO0pik

Output:

2009/11/10 23:00:00 main
2009/11/10 23:00:00 monitor
2009/11/10 23:00:05 len(c) == cap(c)
2009/11/10 23:00:06 log: len(10) cap(10)
2009/11/10 23:00:07 log: len(10) cap(10)
2009/11/10 23:00:08 log: len(10) cap(10)
2009/11/10 23:00:08 len(c) < cap(c)
2009/11/10 23:00:13 main

---

References:

Package reflect

The Go Blog: The Laws of Reflection