44. Go - Goroutine Race Conditions & Mutex

Race Condition Example:

package main

import "fmt"

func main() {
    counter := 0

    for i := 0; i < 100; i++ {
        go func() {
            temp := counter
            temp++
            counter = temp
        }()

    }
    fmt.Println(counter)
}

The counter never reaches 100 (100 goroutines counting suppose to increment count by 1) because each goroutine access the counter value at different point in time and then resets the counter where other goroutines will access later.

package main

import (
    "fmt"
    "time"
)

func main() {
    counter := 0

    for i := 0; i < 101; i++ {
        go func() {
            temp := counter
            temp++
            counter = temp

        }()
        fmt.Println(counter)
        time.Sleep(time.Millisecond * 50)

    }
    fmt.Println(counter)
}

Adding Sleep Helps.


package main

import (
    "fmt"
    "sync"
)

func main() {
    counter := 0

    var mu sync.Mutex
    var wg sync.WaitGroup
    wg.Add(100)

    for i := 0; i < 100; i++ {
        go func() {
            mu.Lock()
            temp := counter
            temp++
            counter = temp
            mu.Unlock()
            wg.Done()
        }()
        //fmt.Println(counter)
    }

    wg.Wait()
    fmt.Println(counter)
}

Using Mutex and WaitGroups allows counter goroutines to reach 100.

Mutex locks variable from usable from other goroutines who are also using same variable.

// sync.Mutex

// mu.Lock()

// mu.Unlock() 


Flexible Mutex for Locking Reading or Writing

// type RWMutex


WaitGroup

// sync.WaitGroup

// wg.Add(INT)

// wg.Done()

// wg.Wait()

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