Go RWMutex: Exclusive vs Shared Lock

In this tutorial, you'll learn about Go RWMutex: Exclusive vs Shared Lock. We cover key concepts, practical examples, and best practices.

RWMutex optimization -- Use sync.RWMutex to allow concurrent reads while excluding writes for better performance.

The Problem

sync.Mutex allows only one goroutine at a time. RWMutex allows unlimited concurrent reads but exclusive writes. Use RLock/RUnlock for read-only operations.

Wrong

var mu sync.Mutex
mu.Lock()
readData() // Only one reader at a time
mu.Unlock()

Output:

// Serialized reads even though no writes happen

Right

var mu sync.RWMutex
// Readers:
mu.RLock()
readData()    // Multiple readers concurrently
mu.RUnlock()
// Writers:
mu.Lock()
writeData()   // Exclusive access
mu.Unlock()

Output:

// 10 concurrent readers can read simultaneously

Prevention

• Use RLock for read-only operations
• Use Lock for write operations
• Writers block all readers and other writers
• Readers don't block other readers
• RWMutex is slower than Mutex for short critical sections

Common Mistakes with sync rwmutex

1. Misunderstanding that String is [Char] with poor performance for large text operations
2. Using foldl instead of foldl' causing stack overflow on large lists
3. Forgetting deriving (Show, Eq) on custom data types needed for debugging

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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