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Avoid shared mutable state by using channels to pass data instead of direct access, as demonstrated with a channel-based counter that eliminates race conditions. 2. Use sync.Mutex or sync.RWMutex to protect shared state like caches or configs, ensuring all access paths are properly locked while avoiding coarse locking. 3. Apply sync/atomic for simple atomic operations on basic types such as counters, using functions like atomic.AddUint64 and atomic.LoadUint64 for lock-free performance. 4. Carry request-scoped data safely across goroutines using context.Context with custom key types to prevent collisions. 5. Favor immutable data structures when sharing data to eliminate the need for synchronization, creating new copies instead of modifying existing ones. The best practices emphasize intentional design: prefer channels, use mutexes and atomics appropriately, leverage context, embrace immutability, and never assume package-level variables are safe under concurrency, always testing with the race detector.

Managing state in concurrent Go applications is one of the most common sources of bugs—especially data races—if not handled carefully. Go encourages concurrency through goroutines and channels, but sharing mutable state across them requires deliberate design. Here’s how to do it right.

1. Avoid Shared Mutable State When Possible

The best way to manage state in concurrent programs is to avoid sharing it altogether. Go’s concurrency philosophy, summarized by the slogan "Do not communicate by sharing memory; share memory by communicating," encourages using channels to pass data between goroutines instead of letting them access the same variables directly.

Example: Using a channel instead of a shared counter

func worker(ch chan int) {
    for i := 0; i < 1000; i   {
        ch <- 1
    }
    close(ch)
}

func main() {
    ch := make(chan int)
    go worker(ch)

    sum := 0
    for val := range ch {
        sum  = val
    }
    fmt.Println("Total:", sum) // 1000
}

Here, the accumulator (sum) lives in one goroutine, and values are sent over a channel. No mutexes, no race conditions.

2. Use sync.Mutex for Controlled Access

When you must share state—like a global config, cache, or session store—protect it with a sync.Mutex or sync.RWMutex.

Example: Thread-safe map with mutex

type SafeCounter struct {
    mu    sync.RWMutex
    count map[string]int
}

func (c *SafeCounter) Inc(key string) {
    c.mu.Lock()
    defer c.mu.Unlock()
    c.count[key]  
}

func (c *SafeCounter) Value(key string) int {
    c.mu.RLock()
    defer c.mu.RUnlock()
    return c.count[key]
}

Use RWMutex when reads are frequent and writes are rare—readers can proceed concurrently, but writers get exclusive access.

?? Common mistake: Forgetting to lock in all code paths, or locking too coarsely (e.g., locking the entire function when only a few lines need protection).

3. Use sync/atomic for Simple Values

For low-level primitives like integers or pointers, sync/atomic provides efficient, lock-free operations. It’s ideal for counters, flags, or sequence generators.

Example: Atomic increment

var ops uint64

for i := 0; i < 50; i   {
    go func() {
        for j := 0; j < 1000; j   {
            atomic.AddUint64(&ops, 1)
        }
    }()
}

time.Sleep(2 * time.Second)
fmt.Println("ops:", atomic.LoadUint64(&ops))

• Functions like atomic.AddX, atomic.LoadX, atomic.StoreX, and atomic.SwapX are available for various types.
• Avoid using atomic for complex data structures—it’s meant for simple types only.

4. Leverage context.Context for Request-Scoped State

When handling HTTP requests or long-running operations, use context.Context to carry request-scoped data (e.g., user IDs, deadlines, trace IDs) across goroutines safely.

ctx := context.WithValue(context.Background(), "userID", "123")
go func(ctx context.Context) {
    if userID, ok := ctx.Value("userID").(string); ok {
        fmt.Println("User:", userID)
    }
}(ctx)

? Best practice: Use custom types for keys to avoid collisions.

type ctxKey string
const userIDKey ctxKey = "user-id"

// Set: ctx := context.WithValue(parent, userIDKey, "456")
// Get: ctx.Value(userIDKey).(string)

Bonus: Use Immutable Data Structures

When sharing data between goroutines, consider making it immutable. Once created, it can be safely read by any number of goroutines without synchronization.

For example, instead of modifying a config struct, create a new copy:

type Config struct {
    Timeout time.Duration
    Debug   bool
}

func (c Config) WithDebug(v bool) Config {
    c.Debug = v  // Copy is modified
    return c
}

Now you can pass copies safely across goroutines.

Summary of Best Practices

• ? Prefer channels over shared memory.
• ? Use sync.Mutex or sync.RWMutex when sharing mutable state.
• ? Use sync/atomic for simple, high-performance counters.
• ? Carry request-scoped data via context.Context.
• ? Favor immutability when possible.
• ? Don’t assume package-level variables are safe to access from multiple goroutines.

Concurrent state management in Go doesn’t have to be complex—just intentional. Use the right tool for the job, and always test with the race detector (go run -race).

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