When Should You Embed Mutexes in Go Structs?

When Is It Appropriate to Embed Mutexes Within Structures in Go?

In Go, structs provide a convenient way to encapsulate related data. Developers often incorporate mutexes into structs to protect concurrent access to their internal fields. This approach raises the question of whether embedded mutexes offer advantages over local or global mutexes.

Embedded vs. Local Mutexes

Embedding a mutex within a struct, as demonstrated in the code you provided, closely associates the mutex with the protected data. This makes its purpose readily apparent and facilitates intuitive usage. For example, to protect the contents of struct A, simply use a.mu.Lock() and a.mu.Unlock().

Embedded vs. Global Mutexes

In cases where only a single instance of a struct exists, it may be appropriate to use a global mutex instead. This allows multiple goroutines to access the struct concurrently. However, if multiple instances of the struct require individual protection, a global mutex becomes inappropriate, as it would limit concurrency to only one instance at a time.

Choosing the Appropriate Solution

The preferred approach depends on the specific circumstances:

• Embedded Mutex: Suitable when multiple instances of the struct need to be protected individually from concurrent access.
• Local Mutex: Useful when the scope of protection is limited to a specific function or block of code.
• Global Mutex: Acceptable when only a single instance of the struct exists and concurrent access is acceptable, or when it is unnecessary to differentiate between multiple instances.

True Embedding

While embedding a mutex as a field is common, it is not considered "true embedding" because the field name is explicitly specified. True embedding removes the field name, as seen in the example provided:

var hits struct {
    sync.Mutex
    n int
}

This allows you to call Lock() and Unlock() directly on the struct itself, without specifying the field name.

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