Go sync.Map vs Mutex+Map — Complete Guide

In this tutorial, you'll learn about Go sync.Map vs Mutex+Map. We cover key concepts, practical examples, and best practices.

sync.Map usage -- Understand when sync.Map is appropriate vs regular map with sync.RWMutex.

The Problem

sync.Map is optimized for specific patterns: write-once/read-many, or disjoint key sets. For general caching, sync.RWMutex + map may be faster and simpler.

Wrong

var m sync.Map
m.Store("key", "value")
val, ok := m.Load("key")

Output:

// Works but may not be optimal for your use case

Right

type Cache struct {
    mu sync.RWMutex
    m  map[string]interface{}
}
func (c *Cache) Get(key string) interface{} {
    c.mu.RLock()
    defer c.mu.RUnlock()
    return c.m[key]
}
func (c *Cache) Set(key string, val interface{}) {
    c.mu.Lock()
    defer c.mu.Unlock()
    c.m[key] = val
}

Output:

// Simple, fast for most use cases

Prevention

• Benchmark before choosing sync.Map
• sync.Map good for: write-once, read-many, disjoint keys
• sync.RWMutex + map is simpler for most cases
• sync.Map has LoadOrStore, LoadAndDelete, Range
• Regular map + mutex is faster for writes

Common Mistakes with cache sync map

1. Mixing let bindings with <- bindings in do notation, producing type errors
2. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors
3. Non-exhaustive pattern matches that compile with warnings then crash at runtime

These mistakes appear frequently in real-world GO code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

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