Race Condition

A race condition is an error that can occur in concurrently running programs when two or more independently executing processess have access to a shared resource, and at least one of them modifies it without proper synchronization, resulting in unexpected behavior. The outcome of the program depends on the timing of a process execution, making it unpredictable and difficult to reproduce potential issues. For example, improper use of a mutex can lead to such an error.

Race Detector

The Go CLI comes with a very useful feature: it can detect whether a given program has race condition errors.

Using it is straightforward; you can run the Go CLI with the -race flag to detect races:

go run -race main.go

Example for a Race Condition Error

type Counter struct {
	sync.Mutex
	value int
}
 
func main() {
	counter := Counter{}
	for i := 0; i < 10; i++ {
		go func(i int) {
			// counter.Lock()
			counter.value++
			// defer counter.Unlock()
		}(i)
	}
	time.Sleep(time.Second)
	counter.Lock()
	defer counter.Unlock()
 
	fmt.Println(counter.value)
}

In the above code snippet, the Lock and Unlock methods are commented out, resulting in a race condition error. Since the anonymous functions running on different goroutines can potentially modify the counter's value nearly simultaneously, it leads to erroneous behavior, and the counter won't show the actual result.