What are the possible consequences if multiple threads modify a map data structure simultaneously?

In Go, the standard map is not thread-safe for concurrent read and write operations from multiple goroutines. If multiple goroutines modify the map simultaneously without synchronization, it can lead to a runtime panic with the message "concurrent map writes" or unpredictable program behavior.

To avoid such issues, synchronization mechanisms such as mutexes (sync.Mutex) or specialized thread-safe data structures should be used, or the sync.Map package, which implements a thread-safe map.

Example using a mutex:

var (
    m = make(map[string]int)
    mu sync.Mutex
)

func write(key string, value int) {
    mu.Lock()
    defer mu.Unlock()
    m[key] = value
}

func read(key string) int {
    mu.Lock()
    defer mu.Unlock()
    return m[key]
}

Without such synchronization, the program may crash or get corrupted data.