Debugging Race Condition in Go with goroutines and Mutex - Unexpected Data Modification
I'm collaborating on a project where I'm encountering a race condition in my Go application that uses goroutines and a Mutex for synchronization. The application is fairly simple and performs concurrent updates to a shared map that stores user sessions. Despite using a Mutex to protect access to the map, I'm still observing unexpected data modifications. Here's a simplified version of what I'm doing: ```go package main import ( "fmt" "sync" "time" ) var ( sessions = make(map[string]string) mu sync.Mutex ) func updateSession(userID, sessionID string) { mu.Lock() // Locking the mutex defer mu.Unlock() // Ensure it's unlocked after the function exits sessions[userID] = sessionID time.Sleep(100 * time.Millisecond) // Simulating some processing time } func main() { var wg sync.WaitGroup for i := 0; i < 10; i++ { wg.Add(1) go func(userID int) { defer wg.Done() updateSession(fmt.Sprintf("user%d", userID), fmt.Sprintf("session%d", userID)) }(i) } wg.Wait() fmt.Println(sessions) } ``` When I run this code, I sometimes get overlapping session IDs for the same user, even though I believe the mutex should prevent concurrent writes. Occasionally, the output shows that different goroutines are writing to the same user ID, resulting in lost updates. I have tried using `atomic` operations as well, but they seem to complicate the implementation unnecessarily. Is there any reason the Mutex might not be working as intended, or is there a better approach to manage concurrent writes to a shared map in Go? I'm using Go version 1.20. This is happening in both development and production on Ubuntu 22.04. Any suggestions would be helpful.