什么时候应该在通道上使用互斥锁？

Question

For the past few weeks I've been wrestling with one (not-so) simple question:

When is it best to use a sync.Mutex and, conversely, when is it best use a chan?

It seems that for a lot of problems either strategy is interchangeable with the other - and that's just the problem!

Take this video found in the Golang documentation. Below, I've taken the liberty to dictate the code in the playground and also translate it to a sync.Mutex equivalent.

Is there a certain problem - encountered in the real world - that warrants the use of one other?

Notes:

• I am a huge fan of this use of chan and struggle to think of a more elegant implementation using sync.Mutex.
• It's worth noting that the chan implementation does more work in the same time (reaches 12)*

Playgrounds:

• Chan implementation
• Mutex implementation

Ping/pong with chan:

package main

import (
    "fmt"
    "time"
)

type Ball struct { hits int }

func main() {
    table := make(chan *Ball)
    go player("ping", table)
    go player("pong", table)

    table <- new(Ball)
    time.Sleep(1 * time.Second)
    <-table
}

func player(name string, table chan *Ball) {
    for {
        ball := <-table
        ball.hits++
        fmt.Println(name, ball.hits)
        time.Sleep(100 * time.Millisecond)
        table <- ball
    }
}

Ping/pong with sync.Mutex:

package main

import (
    "fmt"
    "time"
    "sync"
)

type Ball struct { hits int }

var m =  sync.Mutex{}

func main() {
    ball := new(Ball)
    go player("ping", ball)
    go player("pong", ball)

    time.Sleep(1 * time.Second)
}

func player(name string, ball *Ball) {
    for {
        m.Lock()
        ball.hits++
        fmt.Println(name, ball.hits)
        time.Sleep(100 * time.Millisecond)
        m.Unlock()

    }
}

Answer 1

In some case Channels are best, in some sync.Mutex, for this simple example sync.Mutex is 10x slower than channel:
e.g. here the difference is 101 million (Imagine you need One second counter):

1- Consider this simple code:

package main

import (
    "sync"
    "time"
)

func main() {
    var i rwm
    go func() {
        for {
            i.inc() // free running counter
        }
    }()
    time.Sleep(1 * time.Second)
    println(i.read()) // sampling the counter
}

type rwm struct {
    sync.RWMutex
    i int
}

func (l *rwm) inc() {
    l.Lock()
    defer l.Unlock()
    l.i++
}
func (l *rwm) read() int {
    l.RLock()
    defer l.RUnlock()
    return l.i
}

output:

11227280

---

2- versus this using channel:

package main

import "time"

func main() {
    ch := make(chan int)
    go func() {
        timeout := time.NewTimer(1 * time.Second)
        defer timeout.Stop()
        i := 1
        for {
            select {
            case <-timeout.C:
                ch <- i
                return
            default:
                i++
            }
        }
    }()

    println(<-ch)
}

output:

112362269

---

difference:

112362269-11227280=101134989

112362269/11227280=10x