Go Race

A race condition occurs in Go when two or more goroutines try to access the same resource. It may happen when a variable attempts to read and write the resource without any regard to other routines.

Go Race Condition Example

package main
import (
   "sync"
   "time"
   "math/rand"
   "fmt"
)
var wait sync.WaitGroup
var count int
func  increment(s string)  {
   for i :=0;i<10;i++ {
      x := count
      x++;
      time.Sleep(time.Duration(rand.Intn(4))*time.Millisecond)
      count = x;
      fmt.Println(s, i,"Count: ",count)
      
   }
   wait.Done()
   
}
func main(){
   wait.Add(2)
   go increment("foo: ")
   go increment("bar: ")
   wait.Wait()
   fmt.Println("last count value " ,count)
}

Output:

foo:  0 Count:  1
bar:  0 Count:  1
foo:  1 Count:  2
foo:  2 Count:  3
foo:  3 Count:  4
bar:  1 Count:  2
foo:  4 Count:  5
foo:  5 Count:  6
foo:  6 Count:  7
bar:  2 Count:  3
bar:  3 Count:  4
bar:  4 Count:  5
foo:  7 Count:  8
foo:  8 Count:  9
bar:  5 Count:  6
bar:  6 Count:  7
foo:  9 Count:  10
bar:  7 Count:  8
bar:  8 Count:  9
bar:  9 Count:  10
last count value  10

As you can see in the above example, the count resource is accessed by 2 go routines. Each routine iterates to 10 times. In such case, the count variable should be 20 at last. But it is not so because it is simulating race condition.

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