package main

import (
    "fmt"
    "math/rand"
    "sync"
    "sync/atomic"
    "time"
)

func main() {

    // For our example the state will be a map.
    var state = make(map[int]int)

    var mutex = &sync.Mutex{}

    var readOps uint64
    var writeOps uint64

    // Here we start 100 goroutines to execute repeated reads against the state,
    // once per millisecond in each goroutine.
    for r := 0; r < 100; r++ {
        go func() {
            total := 0
            for {
                // For each read we pick a key to access,
                // Lock() the mutex to ensure exclusive access to the state,
                // read the value at the chosen key, Unlock() the mutex,
                // and increment the readOps count.
                key := rand.Intn(5)
                mutex.Lock()
                total += state[key]
                mutex.Unlock()
                atomic.AddUint64(&readOps, 1)

                time.Sleep(time.Millisecond)
            }
        }()
    }

    // We’ll also start 10 goroutines to simulate writes, using the same pattern we did for reads.
    for w := 0; w < 10; w++ {
        go func() {
            for {
                key := rand.Intn(5)
                val := rand.Intn(100)
                mutex.Lock()
                state[key] = val
                mutex.Unlock()
                atomic.AddUint64(&writeOps, 1)
                time.Sleep(time.Millisecond)
            }
        }()
    }

    time.Sleep(time.Second)

    // Take and report final operation counts.
    readOpsFinal := atomic.LoadUint64(&readOps)
    fmt.Println("readOps:", readOpsFinal)
    writeOpsFinal := atomic.LoadUint64(&writeOps)
    fmt.Println("writeOps:", writeOpsFinal)

    // With a final lock of state, show how it ended up.
    mutex.Lock()
    fmt.Println("state:", state)
    mutex.Unlock()
}

Stdout
Stderr