To Embed or Not to Embed? When Should You Use Mutexes Within Go Structs?

Embedding Mutex in Go Structs

Embedding mutexes within structs is a common practice in Go when it is necessary to control concurrent access to data. However, there are certain scenarios where this approach may not be the most appropriate. This article will delve into the advantages and disadvantages of embedding mutexes in structs, providing guidance on when to use this technique and when to consider alternatives.

Benefits of Embedded Mutexes

• Bundling mutex with protected data: Embedding the mutex within the struct keeps it bundled closely with the data it protects, making it obvious what the mutex is intended to safeguard.
• Instance isolation: Each instance of the struct will have its own mutex, ensuring that modifications made to one instance do not affect others.

Drawbacks of Embedded Mutexes

• Unwieldy syntax: Embedding mutexes can make the code somewhat more verbose and potentially less readable.
• Limited flexibility: If the struct's interface needs to change over time, the changes may require adjusting the embedded mutex, which can be problematic if the mutex is used in multiple locations.

When to Embed Mutexes

Embedding mutexes in structs is suitable in the following scenarios:

• When the mutex protects fields within a struct that are never accessed concurrently outside of the struct.
• When multiple instances of the struct are created, and each instance requires independent protection from concurrent access.

When to Use Alternatives

• Global mutex: If the mutex is intended to protect data that is shared across multiple instances of a struct, a global mutex is a better choice. This ensures that all concurrent accesses to the protected data are synchronized.
• Local mutex: If the concurrency-related logic is localized within a single function or method, using a local mutex is a more efficient and straightforward approach.

Embedded Mutexes in Action

While the given example in the question simply places a mutex as a field within a struct, it is also possible to truly embed a mutex without specifying a field name:

var hits struct {
    sync.Mutex
    n int
}

This syntax allows calling Lock() and Unlock() directly on the struct, as if they were methods defined within it.

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