How to Solve the 'fatal error: concurrent map read and map write' in Go?

"Golang fatal error: concurrent map read and map write" Explained

The error "fatal error: concurrent map read and map write" in Go occurs when multiple goroutines try to access a map concurrently for both reading and writing. This can happen when one goroutine tries to read from the map while another goroutine is concurrently writing to it.

Solutions

sync.RWMutex

Use a sync.RWMutex to control access to the map. This option is suitable for scenarios with single reads and writes (not loops over the map).

var someMap = map[string]string{}
var someMapMutex = sync.RWMutex{}

go func() {
    someMapMutex.Lock()
    someMap["key"] = "value"
    someMapMutex.Unlock()
}()

someMapMutex.RLock()
v, ok := someMap["key"]
someMapMutex.RUnlock()
if !ok {
    fmt.Println("key missing")
    return
}
fmt.Println(v)

syncmap.Map

An alternative is to use a syncmap.Map{}, which is a concurrent map type in Go. It handles race conditions internally and is generally slower than a regular map. However, it excels in for-loop scenarios.

var someMap = syncmap.Map{}

go func() {
    someMap.Store("key", "value")
}()

v, ok := someMap.Load("key")
if !ok {
    fmt.Println("key missing")
    return
}
fmt.Println(v)

// Looping over keys is simplified with syncmap
someMap.Range(func(key, value interface{}) bool {
    val, ok := value.(string)
    if !ok {
        return false // Break iteration
    }
    fmt.Println(key, val)
    return true // Continue iteration
})

General Advice

To prevent this error, it's recommended to test your server with the -race option to identify and eliminate potential race conditions.

go run -race server.go

By implementing these solutions and following these guidelines, you can avoid the "concurrent map read and map write" error and ensure thread-safe access to shared data in your Go code.

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