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What is State Pattern? The State pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. It appears as if the object changed its class. Think of it like a vending machine - it behaves differently when it’s waiting for coins, has coins inserted, is dispensing a product, or is out of stock. Each state has its own set of valid operations and transitions. ...

Go Concurrency Patterns Series: ← Pub/Sub Pattern | Series Overview | Worker Pool → What is the Request/Response Pattern? The Request/Response pattern enables synchronous communication between goroutines, where a sender waits for a response from a receiver. This pattern is essential for RPC-style communication, database queries, API calls, and any scenario where you need to get a result back from an operation. Key Components: Request: Contains data and a response channel Response: Contains result data and/or error information Requester: Sends request and waits for response Responder: Processes request and sends response Real-World Use Cases Database Operations: Query execution with results API Gateways: Forwarding requests to microservices Cache Systems: Get/Set operations with confirmation File Operations: Read/Write with status feedback Validation Services: Input validation with results Authentication: Login requests with tokens Basic Request/Response Implementation package main import ( "fmt" "math/rand" "time" ) // Request represents a request with a response channel type Request struct { ID string Data interface{} Response chan Response } // Response represents the response to a request type Response struct { ID string Result interface{} Error error } // Server processes requests type Server struct { requests chan Request quit chan bool } // NewServer creates a new server func NewServer() *Server { return &Server{ requests: make(chan Request), quit: make(chan bool), } } // Start begins processing requests func (s *Server) Start() { go func() { for { select { case req := <-s.requests: s.processRequest(req) case <-s.quit: return } } }() } // processRequest handles a single request func (s *Server) processRequest(req Request) { // Simulate processing time time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond) // Process the request (example: double the number) var response Response response.ID = req.ID if num, ok := req.Data.(int); ok { response.Result = num * 2 } else { response.Error = fmt.Errorf("invalid data type") } // Send response back req.Response <- response } // SendRequest sends a request and waits for response func (s *Server) SendRequest(id string, data interface{}) (interface{}, error) { responseChan := make(chan Response, 1) request := Request{ ID: id, Data: data, Response: responseChan, } s.requests <- request // Wait for response response := <-responseChan return response.Result, response.Error } // Stop shuts down the server func (s *Server) Stop() { close(s.quit) } func main() { server := NewServer() server.Start() defer server.Stop() // Send multiple requests for i := 1; i <= 5; i++ { result, err := server.SendRequest(fmt.Sprintf("req-%d", i), i*10) if err != nil { fmt.Printf("Request %d failed: %v\n", i, err) } else { fmt.Printf("Request %d result: %v\n", i, result) } } } Request/Response with Timeout package main import ( "context" "fmt" "math/rand" "time" ) // TimedRequest includes context for timeout handling type TimedRequest struct { ID string Data interface{} Response chan TimedResponse Context context.Context } // TimedResponse includes timing information type TimedResponse struct { ID string Result interface{} Error error Duration time.Duration Timestamp time.Time } // TimedServer processes requests with timeout support type TimedServer struct { requests chan TimedRequest quit chan bool } func NewTimedServer() *TimedServer { return &TimedServer{ requests: make(chan TimedRequest, 10), quit: make(chan bool), } } func (ts *TimedServer) Start() { go func() { for { select { case req := <-ts.requests: go ts.processTimedRequest(req) case <-ts.quit: return } } }() } func (ts *TimedServer) processTimedRequest(req TimedRequest) { start := time.Now() // Check if context is already cancelled select { case <-req.Context.Done(): ts.sendResponse(req, nil, req.Context.Err(), start) return default: } // Simulate work with random duration workDuration := time.Duration(rand.Intn(200)) * time.Millisecond select { case <-time.After(workDuration): // Work completed if num, ok := req.Data.(int); ok { ts.sendResponse(req, num*2, nil, start) } else { ts.sendResponse(req, nil, fmt.Errorf("invalid data type"), start) } case <-req.Context.Done(): // Context cancelled during work ts.sendResponse(req, nil, req.Context.Err(), start) } } func (ts *TimedServer) sendResponse(req TimedRequest, result interface{}, err error, start time.Time) { response := TimedResponse{ ID: req.ID, Result: result, Error: err, Duration: time.Since(start), Timestamp: time.Now(), } select { case req.Response <- response: case <-req.Context.Done(): // Client no longer waiting } } // SendRequestWithTimeout sends a request with a timeout func (ts *TimedServer) SendRequestWithTimeout(id string, data interface{}, timeout time.Duration) (interface{}, error) { ctx, cancel := context.WithTimeout(context.Background(), timeout) defer cancel() responseChan := make(chan TimedResponse, 1) request := TimedRequest{ ID: id, Data: data, Response: responseChan, Context: ctx, } select { case ts.requests <- request: case <-ctx.Done(): return nil, ctx.Err() } select { case response := <-responseChan: fmt.Printf("Request %s completed in %v\n", response.ID, response.Duration) return response.Result, response.Error case <-ctx.Done(): return nil, ctx.Err() } } func (ts *TimedServer) Stop() { close(ts.quit) } func main() { server := NewTimedServer() server.Start() defer server.Stop() // Send requests with different timeouts requests := []struct { id string data int timeout time.Duration }{ {"fast", 10, 300 * time.Millisecond}, {"medium", 20, 150 * time.Millisecond}, {"slow", 30, 50 * time.Millisecond}, // This might timeout } for _, req := range requests { result, err := server.SendRequestWithTimeout(req.id, req.data, req.timeout) if err != nil { fmt.Printf("Request %s failed: %v\n", req.id, err) } else { fmt.Printf("Request %s result: %v\n", req.id, result) } } } Future/Promise Pattern package main import ( "context" "fmt" "sync" "time" ) // Future represents a value that will be available in the future type Future struct { mu sync.Mutex done chan struct{} result interface{} err error computed bool } // NewFuture creates a new future func NewFuture() *Future { return &Future{ done: make(chan struct{}), } } // Set sets the future's value func (f *Future) Set(result interface{}, err error) { f.mu.Lock() defer f.mu.Unlock() if f.computed { return // Already set } f.result = result f.err = err f.computed = true close(f.done) } // Get waits for and returns the future's value func (f *Future) Get() (interface{}, error) { <-f.done return f.result, f.err } // GetWithTimeout waits for the value with a timeout func (f *Future) GetWithTimeout(timeout time.Duration) (interface{}, error) { select { case <-f.done: return f.result, f.err case <-time.After(timeout): return nil, fmt.Errorf("timeout waiting for future") } } // GetWithContext waits for the value with context cancellation func (f *Future) GetWithContext(ctx context.Context) (interface{}, error) { select { case <-f.done: return f.result, f.err case <-ctx.Done(): return nil, ctx.Err() } } // IsReady returns true if the future has been computed func (f *Future) IsReady() bool { f.mu.Lock() defer f.mu.Unlock() return f.computed } // AsyncService demonstrates async operations with futures type AsyncService struct { workers chan struct{} } func NewAsyncService(maxWorkers int) *AsyncService { return &AsyncService{ workers: make(chan struct{}, maxWorkers), } } // ProcessAsync starts async processing and returns a future func (as *AsyncService) ProcessAsync(data interface{}) *Future { future := NewFuture() go func() { // Acquire worker slot as.workers <- struct{}{} defer func() { <-as.workers }() // Simulate processing time.Sleep(time.Duration(100+rand.Intn(200)) * time.Millisecond) // Process data if num, ok := data.(int); ok { future.Set(num*num, nil) } else { future.Set(nil, fmt.Errorf("invalid data type")) } }() return future } func main() { service := NewAsyncService(3) // Start multiple async operations futures := make([]*Future, 5) for i := 0; i < 5; i++ { fmt.Printf("Starting async operation %d\n", i+1) futures[i] = service.ProcessAsync((i + 1) * 10) } // Wait for all results fmt.Println("\nWaiting for results...") for i, future := range futures { result, err := future.Get() if err != nil { fmt.Printf("Operation %d failed: %v\n", i+1, err) } else { fmt.Printf("Operation %d result: %v\n", i+1, result) } } // Example with timeout fmt.Println("\nTesting timeout...") timeoutFuture := service.ProcessAsync(100) result, err := timeoutFuture.GetWithTimeout(50 * time.Millisecond) if err != nil { fmt.Printf("Timeout example failed: %v\n", err) } else { fmt.Printf("Timeout example result: %v\n", result) } } Batch Request/Response package main import ( "fmt" "sync" "time" ) // BatchRequest represents multiple requests processed together type BatchRequest struct { ID string Items []interface{} Response chan BatchResponse } // BatchResponse contains results for all items in a batch type BatchResponse struct { ID string Results []BatchResult Error error } // BatchResult represents the result of processing one item type BatchResult struct { Index int Result interface{} Error error } // BatchProcessor processes requests in batches for efficiency type BatchProcessor struct { requests chan BatchRequest batchSize int batchWindow time.Duration quit chan bool } func NewBatchProcessor(batchSize int, batchWindow time.Duration) *BatchProcessor { return &BatchProcessor{ requests: make(chan BatchRequest, 100), batchSize: batchSize, batchWindow: batchWindow, quit: make(chan bool), } } func (bp *BatchProcessor) Start() { go func() { batch := make([]BatchRequest, 0, bp.batchSize) timer := time.NewTimer(bp.batchWindow) timer.Stop() for { select { case req := <-bp.requests: batch = append(batch, req) if len(batch) == 1 { timer.Reset(bp.batchWindow) } if len(batch) >= bp.batchSize { bp.processBatch(batch) batch = batch[:0] timer.Stop() } case <-timer.C: if len(batch) > 0 { bp.processBatch(batch) batch = batch[:0] } case <-bp.quit: if len(batch) > 0 { bp.processBatch(batch) } return } } }() } func (bp *BatchProcessor) processBatch(batch []BatchRequest) { fmt.Printf("Processing batch of %d requests\n", len(batch)) var wg sync.WaitGroup for _, req := range batch { wg.Add(1) go func(r BatchRequest) { defer wg.Done() bp.processRequest(r) }(req) } wg.Wait() } func (bp *BatchProcessor) processRequest(req BatchRequest) { results := make([]BatchResult, len(req.Items)) for i, item := range req.Items { // Simulate processing each item time.Sleep(10 * time.Millisecond) if num, ok := item.(int); ok { results[i] = BatchResult{ Index: i, Result: num * 3, } } else { results[i] = BatchResult{ Index: i, Error: fmt.Errorf("invalid item type at index %d", i), } } } response := BatchResponse{ ID: req.ID, Results: results, } req.Response <- response } // SendBatchRequest sends a batch request and waits for response func (bp *BatchProcessor) SendBatchRequest(id string, items []interface{}) ([]BatchResult, error) { responseChan := make(chan BatchResponse, 1) request := BatchRequest{ ID: id, Items: items, Response: responseChan, } bp.requests <- request response := <-responseChan return response.Results, response.Error } func (bp *BatchProcessor) Stop() { close(bp.quit) } func main() { processor := NewBatchProcessor(3, 100*time.Millisecond) processor.Start() defer processor.Stop() // Send individual batch requests go func() { results, err := processor.SendBatchRequest("batch1", []interface{}{1, 2, 3, 4, 5}) if err != nil { fmt.Printf("Batch 1 failed: %v\n", err) return } fmt.Println("Batch 1 results:") for _, result := range results { if result.Error != nil { fmt.Printf(" Item %d error: %v\n", result.Index, result.Error) } else { fmt.Printf(" Item %d result: %v\n", result.Index, result.Result) } } }() go func() { results, err := processor.SendBatchRequest("batch2", []interface{}{10, 20, 30}) if err != nil { fmt.Printf("Batch 2 failed: %v\n", err) return } fmt.Println("Batch 2 results:") for _, result := range results { if result.Error != nil { fmt.Printf(" Item %d error: %v\n", result.Index, result.Error) } else { fmt.Printf(" Item %d result: %v\n", result.Index, result.Result) } } }() // Wait for processing time.Sleep(500 * time.Millisecond) } Best Practices Always Use Timeouts: Prevent indefinite blocking Handle Context Cancellation: Support graceful cancellation Buffer Response Channels: Avoid blocking responders Error Handling: Always include error information in responses Resource Cleanup: Ensure channels and goroutines are cleaned up Monitoring: Track request/response times and success rates Backpressure: Handle situations when responders are overwhelmed Common Pitfalls Deadlocks: Not buffering response channels Goroutine Leaks: Not handling context cancellation Memory Leaks: Not closing channels properly Blocking Operations: Long-running operations without timeouts Lost Responses: Not handling channel closure Testing Request/Response package main import ( "context" "testing" "time" ) func TestRequestResponse(t *testing.T) { server := NewTimedServer() server.Start() defer server.Stop() // Test successful request result, err := server.SendRequestWithTimeout("test1", 42, 200*time.Millisecond) if err != nil { t.Fatalf("Request failed: %v", err) } if result != 84 { t.Errorf("Expected 84, got %v", result) } // Test timeout _, err = server.SendRequestWithTimeout("test2", 42, 10*time.Millisecond) if err == nil { t.Error("Expected timeout error") } } func TestFuture(t *testing.T) { future := NewFuture() // Test that future is not ready initially if future.IsReady() { t.Error("Future should not be ready initially") } // Set value in goroutine go func() { time.Sleep(50 * time.Millisecond) future.Set("test result", nil) }() // Get value result, err := future.Get() if err != nil { t.Fatalf("Future failed: %v", err) } if result != "test result" { t.Errorf("Expected 'test result', got %v", result) } // Test that future is ready after setting if !future.IsReady() { t.Error("Future should be ready after setting") } } The Request/Response pattern is essential for building synchronous communication systems in Go. It provides the foundation for RPC systems, database operations, and any scenario where you need to wait for a result from an asynchronous operation. ...

Go Concurrency Patterns Series: ← Circuit Breaker | Series Overview | Semaphore Pattern → What is the Rate Limiter Pattern? Rate limiting controls the rate at which operations are performed, preventing system overload and ensuring fair resource usage. It’s essential for protecting services from abuse, managing resource consumption, and maintaining system stability under load. Common Algorithms: Token Bucket: Allows bursts up to bucket capacity Fixed Window: Fixed number of requests per time window Sliding Window: Smooth rate limiting over time Leaky Bucket: Constant output rate regardless of input Real-World Use Cases API Rate Limiting: Prevent API abuse and ensure fair usage Database Throttling: Control database query rates File Processing: Limit file processing rate Network Operations: Control bandwidth usage Background Jobs: Throttle job processing User Actions: Prevent spam and abuse Token Bucket Rate Limiter package main import ( "context" "fmt" "sync" "time" ) // TokenBucket implements the token bucket rate limiting algorithm type TokenBucket struct { mu sync.Mutex capacity int // Maximum number of tokens tokens int // Current number of tokens refillRate int // Tokens added per second lastRefill time.Time // Last refill time } // NewTokenBucket creates a new token bucket rate limiter func NewTokenBucket(capacity, refillRate int) *TokenBucket { return &TokenBucket{ capacity: capacity, tokens: capacity, // Start with full bucket refillRate: refillRate, lastRefill: time.Now(), } } // Allow checks if a request should be allowed func (tb *TokenBucket) Allow() bool { tb.mu.Lock() defer tb.mu.Unlock() tb.refill() if tb.tokens > 0 { tb.tokens-- return true } return false } // AllowN checks if n requests should be allowed func (tb *TokenBucket) AllowN(n int) bool { tb.mu.Lock() defer tb.mu.Unlock() tb.refill() if tb.tokens >= n { tb.tokens -= n return true } return false } // Wait waits until a token is available func (tb *TokenBucket) Wait(ctx context.Context) error { for { if tb.Allow() { return nil } select { case <-time.After(time.Millisecond * 10): continue case <-ctx.Done(): return ctx.Err() } } } // refill adds tokens based on elapsed time func (tb *TokenBucket) refill() { now := time.Now() elapsed := now.Sub(tb.lastRefill) tokensToAdd := int(elapsed.Seconds() * float64(tb.refillRate)) if tokensToAdd > 0 { tb.tokens += tokensToAdd if tb.tokens > tb.capacity { tb.tokens = tb.capacity } tb.lastRefill = now } } // GetStats returns current bucket statistics func (tb *TokenBucket) GetStats() (tokens, capacity int) { tb.mu.Lock() defer tb.mu.Unlock() tb.refill() return tb.tokens, tb.capacity } func main() { // Create a token bucket: 5 tokens capacity, 2 tokens per second refill rate limiter := NewTokenBucket(5, 2) fmt.Println("=== Token Bucket Rate Limiter Demo ===") // Test burst capability fmt.Println("\n--- Testing Burst Capability ---") for i := 1; i <= 7; i++ { allowed := limiter.Allow() tokens, capacity := limiter.GetStats() fmt.Printf("Request %d: %s (tokens: %d/%d)\n", i, allowedStatus(allowed), tokens, capacity) } // Wait for refill fmt.Println("\n--- Waiting 3 seconds for refill ---") time.Sleep(3 * time.Second) // Test after refill fmt.Println("\n--- Testing After Refill ---") for i := 1; i <= 4; i++ { allowed := limiter.Allow() tokens, capacity := limiter.GetStats() fmt.Printf("Request %d: %s (tokens: %d/%d)\n", i, allowedStatus(allowed), tokens, capacity) } // Test AllowN fmt.Println("\n--- Testing AllowN (requesting 3 tokens) ---") allowed := limiter.AllowN(3) tokens, capacity := limiter.GetStats() fmt.Printf("Bulk request: %s (tokens: %d/%d)\n", allowedStatus(allowed), tokens, capacity) } func allowedStatus(allowed bool) string { if allowed { return " ALLOWED" } return " DENIED" } Sliding Window Rate Limiter package main import ( "fmt" "sync" "time" ) // SlidingWindow implements sliding window rate limiting type SlidingWindow struct { mu sync.Mutex requests []time.Time limit int // Maximum requests per window window time.Duration // Time window duration } // NewSlidingWindow creates a new sliding window rate limiter func NewSlidingWindow(limit int, window time.Duration) *SlidingWindow { return &SlidingWindow{ requests: make([]time.Time, 0), limit: limit, window: window, } } // Allow checks if a request should be allowed func (sw *SlidingWindow) Allow() bool { sw.mu.Lock() defer sw.mu.Unlock() now := time.Now() sw.cleanOldRequests(now) if len(sw.requests) < sw.limit { sw.requests = append(sw.requests, now) return true } return false } // cleanOldRequests removes requests outside the current window func (sw *SlidingWindow) cleanOldRequests(now time.Time) { cutoff := now.Add(-sw.window) // Find first request within window start := 0 for i, req := range sw.requests { if req.After(cutoff) { start = i break } start = len(sw.requests) // All requests are old } // Keep only recent requests if start > 0 { copy(sw.requests, sw.requests[start:]) sw.requests = sw.requests[:len(sw.requests)-start] } } // GetStats returns current window statistics func (sw *SlidingWindow) GetStats() (current, limit int, window time.Duration) { sw.mu.Lock() defer sw.mu.Unlock() sw.cleanOldRequests(time.Now()) return len(sw.requests), sw.limit, sw.window } // GetRequestTimes returns timestamps of requests in current window func (sw *SlidingWindow) GetRequestTimes() []time.Time { sw.mu.Lock() defer sw.mu.Unlock() sw.cleanOldRequests(time.Now()) result := make([]time.Time, len(sw.requests)) copy(result, sw.requests) return result } func main() { // Create sliding window: 3 requests per 2 seconds limiter := NewSlidingWindow(3, 2*time.Second) fmt.Println("=== Sliding Window Rate Limiter Demo ===") fmt.Println("Limit: 3 requests per 2 seconds") // Test requests over time for i := 1; i <= 8; i++ { allowed := limiter.Allow() current, limit, window := limiter.GetStats() fmt.Printf("Request %d: %s (current: %d/%d in %v window)\n", i, allowedStatus(allowed), current, limit, window) if i == 4 { fmt.Println("--- Waiting 1 second ---") time.Sleep(1 * time.Second) } else if i == 6 { fmt.Println("--- Waiting 1.5 seconds ---") time.Sleep(1500 * time.Millisecond) } else { time.Sleep(200 * time.Millisecond) } } // Show request timeline fmt.Println("\n--- Request Timeline ---") requests := limiter.GetRequestTimes() now := time.Now() for i, req := range requests { age := now.Sub(req) fmt.Printf("Request %d: %v ago\n", i+1, age.Round(time.Millisecond)) } } Fixed Window Rate Limiter package main import ( "fmt" "sync" "time" ) // FixedWindow implements fixed window rate limiting type FixedWindow struct { mu sync.Mutex limit int // Maximum requests per window window time.Duration // Window duration currentCount int // Current window request count windowStart time.Time // Current window start time } // NewFixedWindow creates a new fixed window rate limiter func NewFixedWindow(limit int, window time.Duration) *FixedWindow { return &FixedWindow{ limit: limit, window: window, windowStart: time.Now(), } } // Allow checks if a request should be allowed func (fw *FixedWindow) Allow() bool { fw.mu.Lock() defer fw.mu.Unlock() now := time.Now() // Check if we need to start a new window if now.Sub(fw.windowStart) >= fw.window { fw.currentCount = 0 fw.windowStart = now } if fw.currentCount < fw.limit { fw.currentCount++ return true } return false } // GetStats returns current window statistics func (fw *FixedWindow) GetStats() (current, limit int, windowRemaining time.Duration) { fw.mu.Lock() defer fw.mu.Unlock() now := time.Now() elapsed := now.Sub(fw.windowStart) if elapsed >= fw.window { return 0, fw.limit, fw.window } return fw.currentCount, fw.limit, fw.window - elapsed } func main() { // Create fixed window: 3 requests per 2 seconds limiter := NewFixedWindow(3, 2*time.Second) fmt.Println("=== Fixed Window Rate Limiter Demo ===") fmt.Println("Limit: 3 requests per 2 seconds") // Test requests over time for i := 1; i <= 10; i++ { allowed := limiter.Allow() current, limit, remaining := limiter.GetStats() fmt.Printf("Request %d: %s (current: %d/%d, window resets in: %v)\n", i, allowedStatus(allowed), current, limit, remaining.Round(time.Millisecond)) time.Sleep(400 * time.Millisecond) } } Advanced Rate Limiter with Multiple Algorithms package main import ( "context" "fmt" "sync" "time" ) // RateLimiterType represents different rate limiting algorithms type RateLimiterType int const ( TokenBucketType RateLimiterType = iota SlidingWindowType FixedWindowType ) // RateLimiter interface for different rate limiting algorithms type RateLimiter interface { Allow() bool Wait(ctx context.Context) error GetStats() map[string]interface{} } // MultiRateLimiter combines multiple rate limiters type MultiRateLimiter struct { limiters []RateLimiter names []string } // NewMultiRateLimiter creates a new multi-algorithm rate limiter func NewMultiRateLimiter() *MultiRateLimiter { return &MultiRateLimiter{ limiters: make([]RateLimiter, 0), names: make([]string, 0), } } // AddLimiter adds a rate limiter with a name func (mrl *MultiRateLimiter) AddLimiter(name string, limiter RateLimiter) { mrl.limiters = append(mrl.limiters, limiter) mrl.names = append(mrl.names, name) } // Allow checks if request is allowed by all limiters func (mrl *MultiRateLimiter) Allow() bool { for _, limiter := range mrl.limiters { if !limiter.Allow() { return false } } return true } // Wait waits until all limiters allow the request func (mrl *MultiRateLimiter) Wait(ctx context.Context) error { for _, limiter := range mrl.limiters { if err := limiter.Wait(ctx); err != nil { return err } } return nil } // GetStats returns stats from all limiters func (mrl *MultiRateLimiter) GetStats() map[string]interface{} { stats := make(map[string]interface{}) for i, limiter := range mrl.limiters { stats[mrl.names[i]] = limiter.GetStats() } return stats } // Enhanced TokenBucket with RateLimiter interface type EnhancedTokenBucket struct { *TokenBucket } func (etb *EnhancedTokenBucket) GetStats() map[string]interface{} { tokens, capacity := etb.TokenBucket.GetStats() return map[string]interface{}{ "type": "token_bucket", "tokens": tokens, "capacity": capacity, "rate": etb.refillRate, } } // Enhanced SlidingWindow with RateLimiter interface type EnhancedSlidingWindow struct { *SlidingWindow } func (esw *EnhancedSlidingWindow) Wait(ctx context.Context) error { for { if esw.Allow() { return nil } select { case <-time.After(time.Millisecond * 10): continue case <-ctx.Done(): return ctx.Err() } } } func (esw *EnhancedSlidingWindow) GetStats() map[string]interface{} { current, limit, window := esw.SlidingWindow.GetStats() return map[string]interface{}{ "type": "sliding_window", "current": current, "limit": limit, "window": window.String(), } } // Enhanced FixedWindow with RateLimiter interface type EnhancedFixedWindow struct { *FixedWindow } func (efw *EnhancedFixedWindow) Wait(ctx context.Context) error { for { if efw.Allow() { return nil } select { case <-time.After(time.Millisecond * 10): continue case <-ctx.Done(): return ctx.Err() } } } func (efw *EnhancedFixedWindow) GetStats() map[string]interface{} { current, limit, remaining := efw.FixedWindow.GetStats() return map[string]interface{}{ "type": "fixed_window", "current": current, "limit": limit, "remaining": remaining.String(), } } // RateLimitedService demonstrates rate limiting in a service type RateLimitedService struct { limiter RateLimiter mu sync.Mutex stats struct { totalRequests int allowedRequests int deniedRequests int } } // NewRateLimitedService creates a new rate limited service func NewRateLimitedService(limiter RateLimiter) *RateLimitedService { return &RateLimitedService{ limiter: limiter, } } // ProcessRequest processes a request with rate limiting func (rls *RateLimitedService) ProcessRequest(ctx context.Context, requestID string) error { rls.mu.Lock() rls.stats.totalRequests++ rls.mu.Unlock() if !rls.limiter.Allow() { rls.mu.Lock() rls.stats.deniedRequests++ rls.mu.Unlock() return fmt.Errorf("request %s denied by rate limiter", requestID) } rls.mu.Lock() rls.stats.allowedRequests++ rls.mu.Unlock() // Simulate processing time.Sleep(50 * time.Millisecond) fmt.Printf(" Processed request %s\n", requestID) return nil } // GetServiceStats returns service statistics func (rls *RateLimitedService) GetServiceStats() map[string]interface{} { rls.mu.Lock() defer rls.mu.Unlock() return map[string]interface{}{ "total_requests": rls.stats.totalRequests, "allowed_requests": rls.stats.allowedRequests, "denied_requests": rls.stats.deniedRequests, "rate_limiter": rls.limiter.GetStats(), } } func main() { // Create multi-algorithm rate limiter multiLimiter := NewMultiRateLimiter() // Add different rate limiters multiLimiter.AddLimiter("token_bucket", &EnhancedTokenBucket{ TokenBucket: NewTokenBucket(5, 2), // 5 tokens, 2 per second }) multiLimiter.AddLimiter("sliding_window", &EnhancedSlidingWindow{ SlidingWindow: NewSlidingWindow(3, 2*time.Second), // 3 requests per 2 seconds }) multiLimiter.AddLimiter("fixed_window", &EnhancedFixedWindow{ FixedWindow: NewFixedWindow(4, 3*time.Second), // 4 requests per 3 seconds }) service := NewRateLimitedService(multiLimiter) fmt.Println("=== Multi-Algorithm Rate Limiter Demo ===") fmt.Println("Using Token Bucket (5 tokens, 2/sec) + Sliding Window (3/2sec) + Fixed Window (4/3sec)") // Simulate concurrent requests var wg sync.WaitGroup for i := 1; i <= 15; i++ { wg.Add(1) go func(id int) { defer wg.Done() ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second) defer cancel() requestID := fmt.Sprintf("req-%d", id) err := service.ProcessRequest(ctx, requestID) if err != nil { fmt.Printf(" %v\n", err) } }(i) time.Sleep(200 * time.Millisecond) } wg.Wait() // Print final statistics fmt.Println("\n=== Final Statistics ===") stats := service.GetServiceStats() fmt.Printf("Total Requests: %d\n", stats["total_requests"]) fmt.Printf("Allowed Requests: %d\n", stats["allowed_requests"]) fmt.Printf("Denied Requests: %d\n", stats["denied_requests"]) fmt.Println("\nRate Limiter Details:") rateLimiterStats := stats["rate_limiter"].(map[string]interface{}) for name, limiterStats := range rateLimiterStats { fmt.Printf(" %s: %+v\n", name, limiterStats) } } Best Practices Choose Right Algorithm: Select based on your specific requirements Token Bucket: Allow bursts, good for APIs Sliding Window: Smooth rate limiting Fixed Window: Simple, memory efficient Configure Appropriately: Set limits based on system capacity Handle Rejections Gracefully: Provide meaningful error messages Monitor Metrics: Track allowed/denied requests and adjust limits Use Context: Support cancellation in Wait operations Consider Distributed Systems: Use Redis or similar for distributed rate limiting Implement Backoff: Add exponential backoff for denied requests Common Pitfalls Too Restrictive: Setting limits too low affects user experience Too Permissive: High limits don’t protect against abuse Memory Leaks: Not cleaning old requests in sliding window Race Conditions: Not properly synchronizing access to counters Ignoring Bursts: Fixed windows can allow double the limit at boundaries Rate limiting is essential for protecting services from overload and ensuring fair resource usage. Choose the right algorithm based on your requirements and always monitor the effectiveness of your rate limiting strategy. ...

Go Concurrency Patterns Series: ← Fan-Out/Fan-In | Series Overview | Request/Response → What is the Pub/Sub Pattern? The Publisher/Subscriber (Pub/Sub) pattern is a messaging pattern where publishers send messages without knowing who will receive them, and subscribers receive messages without knowing who sent them. This creates a loosely coupled system where components can communicate through events without direct dependencies. Key Components: Publisher: Sends messages/events Subscriber: Receives and processes messages/events Message Broker: Routes messages from publishers to subscribers Topics/Channels: Categories for organizing messages Real-World Use Cases Event-Driven Architecture: Microservices communication Real-Time Notifications: User activity feeds, alerts Data Streaming: Log aggregation, metrics collection UI Updates: React to state changes across components Workflow Orchestration: Trigger actions based on events Cache Invalidation: Notify when data changes Basic Pub/Sub Implementation package main import ( "fmt" "sync" "time" ) // Message represents a pub/sub message type Message struct { Topic string Payload interface{} } // Subscriber represents a message handler type Subscriber func(Message) // PubSub is a simple in-memory pub/sub system type PubSub struct { mu sync.RWMutex subscribers map[string][]Subscriber closed bool } // NewPubSub creates a new pub/sub instance func NewPubSub() *PubSub { return &PubSub{ subscribers: make(map[string][]Subscriber), } } // Subscribe adds a subscriber to a topic func (ps *PubSub) Subscribe(topic string, subscriber Subscriber) { ps.mu.Lock() defer ps.mu.Unlock() if ps.closed { return } ps.subscribers[topic] = append(ps.subscribers[topic], subscriber) } // Publish sends a message to all subscribers of a topic func (ps *PubSub) Publish(topic string, payload interface{}) { ps.mu.RLock() defer ps.mu.RUnlock() if ps.closed { return } message := Message{ Topic: topic, Payload: payload, } // Send to all subscribers asynchronously for _, subscriber := range ps.subscribers[topic] { go subscriber(message) } } // Close shuts down the pub/sub system func (ps *PubSub) Close() { ps.mu.Lock() defer ps.mu.Unlock() ps.closed = true } func main() { pubsub := NewPubSub() defer pubsub.Close() // Subscribe to user events pubsub.Subscribe("user.created", func(msg Message) { fmt.Printf("Email service: Welcome %v!\n", msg.Payload) }) pubsub.Subscribe("user.created", func(msg Message) { fmt.Printf("Analytics: New user registered: %v\n", msg.Payload) }) pubsub.Subscribe("user.deleted", func(msg Message) { fmt.Printf("Cleanup service: Remove user data for %v\n", msg.Payload) }) // Publish events pubsub.Publish("user.created", "[email protected]") pubsub.Publish("user.created", "[email protected]") pubsub.Publish("user.deleted", "[email protected]") // Wait for async processing time.Sleep(100 * time.Millisecond) } Advanced Pub/Sub with Channels package main import ( "context" "fmt" "sync" "time" ) // Event represents a structured event type Event struct { ID string Type string Timestamp time.Time Data interface{} } // Subscription represents an active subscription type Subscription struct { ID string Topic string Channel chan Event Filter func(Event) bool cancel context.CancelFunc } // Close cancels the subscription func (s *Subscription) Close() { if s.cancel != nil { s.cancel() } } // EventBus is a channel-based pub/sub system type EventBus struct { mu sync.RWMutex subscriptions map[string][]*Subscription buffer int closed bool } // NewEventBus creates a new event bus func NewEventBus(bufferSize int) *EventBus { return &EventBus{ subscriptions: make(map[string][]*Subscription), buffer: bufferSize, } } // Subscribe creates a new subscription with optional filtering func (eb *EventBus) Subscribe(ctx context.Context, topic string, filter func(Event) bool) *Subscription { eb.mu.Lock() defer eb.mu.Unlock() if eb.closed { return nil } subCtx, cancel := context.WithCancel(ctx) subscription := &Subscription{ ID: fmt.Sprintf("sub-%d", time.Now().UnixNano()), Topic: topic, Channel: make(chan Event, eb.buffer), Filter: filter, cancel: cancel, } eb.subscriptions[topic] = append(eb.subscriptions[topic], subscription) // Clean up subscription when context is cancelled go func() { <-subCtx.Done() eb.unsubscribe(subscription) close(subscription.Channel) }() return subscription } // unsubscribe removes a subscription func (eb *EventBus) unsubscribe(sub *Subscription) { eb.mu.Lock() defer eb.mu.Unlock() subs := eb.subscriptions[sub.Topic] for i, s := range subs { if s.ID == sub.ID { eb.subscriptions[sub.Topic] = append(subs[:i], subs[i+1:]...) break } } } // Publish sends an event to all matching subscribers func (eb *EventBus) Publish(event Event) { eb.mu.RLock() defer eb.mu.RUnlock() if eb.closed { return } event.Timestamp = time.Now() for _, subscription := range eb.subscriptions[event.Type] { // Apply filter if present if subscription.Filter != nil && !subscription.Filter(event) { continue } // Non-blocking send select { case subscription.Channel <- event: default: // Channel is full, could log this fmt.Printf("Warning: Subscription %s channel is full\n", subscription.ID) } } } // Close shuts down the event bus func (eb *EventBus) Close() { eb.mu.Lock() defer eb.mu.Unlock() eb.closed = true // Close all subscriptions for _, subs := range eb.subscriptions { for _, sub := range subs { sub.Close() } } } func main() { ctx := context.Background() eventBus := NewEventBus(10) defer eventBus.Close() // Subscribe to all user events userSub := eventBus.Subscribe(ctx, "user", nil) // Subscribe to only high-priority events prioritySub := eventBus.Subscribe(ctx, "user", func(e Event) bool { if data, ok := e.Data.(map[string]interface{}); ok { return data["priority"] == "high" } return false }) // Start event processors go func() { for event := range userSub.Channel { fmt.Printf("User processor: %s - %v\n", event.Type, event.Data) } }() go func() { for event := range prioritySub.Channel { fmt.Printf("Priority processor: %s - %v\n", event.Type, event.Data) } }() // Publish events eventBus.Publish(Event{ ID: "1", Type: "user", Data: map[string]interface{}{ "action": "login", "user": "john", "priority": "low", }, }) eventBus.Publish(Event{ ID: "2", Type: "user", Data: map[string]interface{}{ "action": "payment", "user": "jane", "priority": "high", }, }) time.Sleep(100 * time.Millisecond) } Persistent Pub/Sub with Replay package main import ( "context" "fmt" "sync" "time" ) // StoredEvent represents an event with storage metadata type StoredEvent struct { Event Sequence int64 Stored time.Time } // PersistentEventBus stores events and supports replay type PersistentEventBus struct { mu sync.RWMutex events []StoredEvent sequence int64 subs map[string][]*PersistentSubscription closed bool } // PersistentSubscription supports replay from a specific point type PersistentSubscription struct { ID string Topic string Channel chan StoredEvent FromSeq int64 cancel context.CancelFunc } func (s *PersistentSubscription) Close() { if s.cancel != nil { s.cancel() } } // NewPersistentEventBus creates a new persistent event bus func NewPersistentEventBus() *PersistentEventBus { return &PersistentEventBus{ events: make([]StoredEvent, 0), subs: make(map[string][]*PersistentSubscription), } } // Subscribe creates a subscription with optional replay func (peb *PersistentEventBus) Subscribe(ctx context.Context, topic string, fromSequence int64) *PersistentSubscription { peb.mu.Lock() defer peb.mu.Unlock() if peb.closed { return nil } subCtx, cancel := context.WithCancel(ctx) sub := &PersistentSubscription{ ID: fmt.Sprintf("psub-%d", time.Now().UnixNano()), Topic: topic, Channel: make(chan StoredEvent, 100), FromSeq: fromSequence, cancel: cancel, } peb.subs[topic] = append(peb.subs[topic], sub) // Replay historical events if requested if fromSequence >= 0 { go peb.replayEvents(sub) } // Clean up on context cancellation go func() { <-subCtx.Done() peb.unsubscribe(sub) close(sub.Channel) }() return sub } // replayEvents sends historical events to a subscription func (peb *PersistentEventBus) replayEvents(sub *PersistentSubscription) { peb.mu.RLock() defer peb.mu.RUnlock() for _, storedEvent := range peb.events { if storedEvent.Sequence >= sub.FromSeq && storedEvent.Type == sub.Topic { select { case sub.Channel <- storedEvent: default: // Channel full, skip } } } } // unsubscribe removes a subscription func (peb *PersistentEventBus) unsubscribe(sub *PersistentSubscription) { peb.mu.Lock() defer peb.mu.Unlock() subs := peb.subs[sub.Topic] for i, s := range subs { if s.ID == sub.ID { peb.subs[sub.Topic] = append(subs[:i], subs[i+1:]...) break } } } // Publish stores and distributes an event func (peb *PersistentEventBus) Publish(event Event) int64 { peb.mu.Lock() defer peb.mu.Unlock() if peb.closed { return -1 } peb.sequence++ storedEvent := StoredEvent{ Event: event, Sequence: peb.sequence, Stored: time.Now(), } // Store event peb.events = append(peb.events, storedEvent) // Distribute to current subscribers for _, sub := range peb.subs[event.Type] { select { case sub.Channel <- storedEvent: default: // Channel full } } return peb.sequence } // GetLastSequence returns the last event sequence number func (peb *PersistentEventBus) GetLastSequence() int64 { peb.mu.RLock() defer peb.mu.RUnlock() return peb.sequence } func main() { ctx := context.Background() eventBus := NewPersistentEventBus() // Publish some initial events eventBus.Publish(Event{ID: "1", Type: "order", Data: "Order created"}) eventBus.Publish(Event{ID: "2", Type: "order", Data: "Order paid"}) eventBus.Publish(Event{ID: "3", Type: "order", Data: "Order shipped"}) fmt.Printf("Published 3 events, last sequence: %d\n", eventBus.GetLastSequence()) // Subscribe from the beginning (replay all events) replaySub := eventBus.Subscribe(ctx, "order", 0) // Subscribe from current point (no replay) liveSub := eventBus.Subscribe(ctx, "order", -1) // Process replayed events go func() { fmt.Println("Replay subscription:") for event := range replaySub.Channel { fmt.Printf(" Replayed: seq=%d, %v\n", event.Sequence, event.Data) } }() // Process live events go func() { fmt.Println("Live subscription:") for event := range liveSub.Channel { fmt.Printf(" Live: seq=%d, %v\n", event.Sequence, event.Data) } }() time.Sleep(100 * time.Millisecond) // Publish new events eventBus.Publish(Event{ID: "4", Type: "order", Data: "Order delivered"}) eventBus.Publish(Event{ID: "5", Type: "order", Data: "Order completed"}) time.Sleep(100 * time.Millisecond) replaySub.Close() liveSub.Close() } Typed Pub/Sub System package main import ( "context" "fmt" "reflect" "sync" ) // TypedEventBus provides type-safe pub/sub type TypedEventBus struct { mu sync.RWMutex handlers map[reflect.Type][]reflect.Value closed bool } // NewTypedEventBus creates a new typed event bus func NewTypedEventBus() *TypedEventBus { return &TypedEventBus{ handlers: make(map[reflect.Type][]reflect.Value), } } // Subscribe registers a handler for a specific event type func (teb *TypedEventBus) Subscribe(handler interface{}) { teb.mu.Lock() defer teb.mu.Unlock() if teb.closed { return } handlerValue := reflect.ValueOf(handler) handlerType := handlerValue.Type() // Validate handler signature: func(EventType) if handlerType.Kind() != reflect.Func || handlerType.NumIn() != 1 || handlerType.NumOut() != 0 { panic("Handler must be func(EventType)") } eventType := handlerType.In(0) teb.handlers[eventType] = append(teb.handlers[eventType], handlerValue) } // Publish sends an event to all registered handlers func (teb *TypedEventBus) Publish(event interface{}) { teb.mu.RLock() defer teb.mu.RUnlock() if teb.closed { return } eventType := reflect.TypeOf(event) eventValue := reflect.ValueOf(event) for _, handler := range teb.handlers[eventType] { go handler.Call([]reflect.Value{eventValue}) } } // Event types type UserCreated struct { UserID string Email string } type OrderPlaced struct { OrderID string UserID string Amount float64 } type PaymentProcessed struct { PaymentID string OrderID string Success bool } func main() { eventBus := NewTypedEventBus() // Subscribe to different event types eventBus.Subscribe(func(event UserCreated) { fmt.Printf("Email service: Send welcome email to %s\n", event.Email) }) eventBus.Subscribe(func(event UserCreated) { fmt.Printf("Analytics: Track user registration %s\n", event.UserID) }) eventBus.Subscribe(func(event OrderPlaced) { fmt.Printf("Inventory: Reserve items for order %s\n", event.OrderID) }) eventBus.Subscribe(func(event OrderPlaced) { fmt.Printf("Payment: Process payment for order %s, amount $%.2f\n", event.OrderID, event.Amount) }) eventBus.Subscribe(func(event PaymentProcessed) { if event.Success { fmt.Printf("Fulfillment: Ship order %s\n", event.OrderID) } else { fmt.Printf("Orders: Cancel order %s due to payment failure\n", event.OrderID) } }) // Publish events eventBus.Publish(UserCreated{ UserID: "user123", Email: "[email protected]", }) eventBus.Publish(OrderPlaced{ OrderID: "order456", UserID: "user123", Amount: 99.99, }) eventBus.Publish(PaymentProcessed{ PaymentID: "pay789", OrderID: "order456", Success: true, }) // Wait for async processing time.Sleep(100 * time.Millisecond) } Best Practices Async Processing: Handle events asynchronously to avoid blocking publishers Error Handling: Implement proper error handling in subscribers Buffering: Use buffered channels to handle bursts of events Graceful Shutdown: Ensure clean shutdown of all subscribers Dead Letter Queues: Handle failed message processing Monitoring: Track message rates, processing times, and failures Type Safety: Use typed events when possible Idempotency: Design subscribers to handle duplicate messages Common Pitfalls Memory Leaks: Not closing subscriptions properly Blocking Publishers: Slow subscribers blocking the entire system Lost Messages: Not handling channel buffer overflows Circular Dependencies: Events triggering other events in loops No Error Handling: Panics in subscribers affecting the system Testing Pub/Sub Systems package main import ( "context" "testing" "time" ) func TestEventBus(t *testing.T) { eventBus := NewEventBus(10) defer eventBus.Close() ctx, cancel := context.WithTimeout(context.Background(), time.Second) defer cancel() // Subscribe to events sub := eventBus.Subscribe(ctx, "test", nil) // Publish event testEvent := Event{ ID: "test1", Type: "test", Data: "test data", } eventBus.Publish(testEvent) // Verify event received select { case received := <-sub.Channel: if received.ID != testEvent.ID { t.Errorf("Expected event ID %s, got %s", testEvent.ID, received.ID) } case <-time.After(100 * time.Millisecond): t.Error("Event not received within timeout") } } The Pub/Sub pattern is fundamental for building scalable, event-driven systems in Go. It enables loose coupling between components and supports complex workflows through simple event-based communication. ...

What is Template Method Pattern? The Template Method pattern is a behavioral design pattern that defines the skeleton of an algorithm in a base class and lets subclasses override specific steps without changing the algorithm’s structure. Think of it like a recipe - the overall cooking process is the same (prepare ingredients, cook, serve), but the specific steps can vary depending on what you’re making. In Go, since we don’t have traditional inheritance, we implement this pattern using composition and interfaces, which actually makes it more flexible and idiomatic. ...

Go Concurrency Patterns Series: ← WaitGroup Pattern | Series Overview | Context Pattern → What is the Once Pattern? The Once pattern uses sync.Once to ensure that a piece of code executes exactly once, regardless of how many goroutines call it. This is essential for thread-safe initialization, singleton patterns, and one-time setup operations in concurrent programs. Key Characteristics: Thread-safe: Multiple goroutines can call it safely Exactly once: Code executes only on the first call Blocking: Subsequent calls wait for the first execution to complete No return values: The function passed to Do() cannot return values Real-World Use Cases Singleton Initialization: Create single instances of objects Configuration Loading: Load config files once at startup Database Connections: Initialize connection pools Logger Setup: Configure logging systems Resource Initialization: Set up expensive resources Feature Flags: Initialize feature flag systems Basic Once Usage package main import ( "fmt" "sync" "time" ) var ( instance *Database once sync.Once ) // Database represents a database connection type Database struct { ConnectionString string IsConnected bool } // Connect simulates database connection func (db *Database) Connect() { fmt.Println("Connecting to database...") time.Sleep(100 * time.Millisecond) // Simulate connection time db.IsConnected = true fmt.Println("Database connected!") } // GetDatabase returns the singleton database instance func GetDatabase() *Database { once.Do(func() { fmt.Println("Initializing database instance...") instance = &Database{ ConnectionString: "localhost:5432", } instance.Connect() }) return instance } func main() { var wg sync.WaitGroup // Multiple goroutines trying to get database instance for i := 0; i < 5; i++ { wg.Add(1) go func(id int) { defer wg.Done() fmt.Printf("Goroutine %d requesting database\n", id) db := GetDatabase() fmt.Printf("Goroutine %d got database: %+v\n", id, db) }(i) } wg.Wait() // Verify all goroutines got the same instance fmt.Printf("Final instance: %p\n", GetDatabase()) } Configuration Manager with Once package main import ( "encoding/json" "fmt" "os" "sync" ) // Config represents application configuration type Config struct { DatabaseURL string `json:"database_url"` APIKey string `json:"api_key"` Debug bool `json:"debug"` Port int `json:"port"` } // ConfigManager manages application configuration type ConfigManager struct { config *Config once sync.Once err error } // NewConfigManager creates a new config manager func NewConfigManager() *ConfigManager { return &ConfigManager{} } // loadConfig loads configuration from file func (cm *ConfigManager) loadConfig() { fmt.Println("Loading configuration...") // Simulate config file reading configData := `{ "database_url": "postgres://localhost:5432/myapp", "api_key": "secret-api-key-123", "debug": true, "port": 8080 }` var config Config if err := json.Unmarshal([]byte(configData), &config); err != nil { cm.err = fmt.Errorf("failed to parse config: %w", err) return } cm.config = &config fmt.Println("Configuration loaded successfully!") } // GetConfig returns the configuration, loading it once if needed func (cm *ConfigManager) GetConfig() (*Config, error) { cm.once.Do(cm.loadConfig) return cm.config, cm.err } func main() { configManager := NewConfigManager() var wg sync.WaitGroup // Multiple goroutines accessing configuration for i := 0; i < 3; i++ { wg.Add(1) go func(id int) { defer wg.Done() config, err := configManager.GetConfig() if err != nil { fmt.Printf("Goroutine %d: Error loading config: %v\n", id, err) return } fmt.Printf("Goroutine %d: Port=%d, Debug=%v\n", id, config.Port, config.Debug) }(i) } wg.Wait() } Logger Initialization with Once package main import ( "fmt" "log" "os" "sync" ) // Logger wraps the standard logger with additional functionality type Logger struct { *log.Logger level string } var ( logger *Logger loggerOnce sync.Once ) // initLogger initializes the global logger func initLogger() { fmt.Println("Initializing logger...") // Create log file file, err := os.OpenFile("app.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666) if err != nil { log.Fatalln("Failed to open log file:", err) } logger = &Logger{ Logger: log.New(file, "APP: ", log.Ldate|log.Ltime|log.Lshortfile), level: "INFO", } logger.Println("Logger initialized") fmt.Println("Logger setup complete!") } // GetLogger returns the singleton logger instance func GetLogger() *Logger { loggerOnce.Do(initLogger) return logger } // Info logs an info message func (l *Logger) Info(msg string) { l.Printf("[INFO] %s", msg) } // Error logs an error message func (l *Logger) Error(msg string) { l.Printf("[ERROR] %s", msg) } func main() { var wg sync.WaitGroup // Multiple goroutines using the logger for i := 0; i < 5; i++ { wg.Add(1) go func(id int) { defer wg.Done() logger := GetLogger() logger.Info(fmt.Sprintf("Message from goroutine %d", id)) if id%2 == 0 { logger.Error(fmt.Sprintf("Error from goroutine %d", id)) } }(i) } wg.Wait() // Clean up if logger != nil { logger.Info("Application shutting down") } } Resource Pool Initialization package main import ( "fmt" "sync" "time" ) // Connection represents a database connection type Connection struct { ID int Connected bool } // Connect simulates connecting to database func (c *Connection) Connect() error { time.Sleep(50 * time.Millisecond) // Simulate connection time c.Connected = true return nil } // Close simulates closing the connection func (c *Connection) Close() error { c.Connected = false return nil } // ConnectionPool manages a pool of database connections type ConnectionPool struct { connections []*Connection available chan *Connection once sync.Once initErr error } // NewConnectionPool creates a new connection pool func NewConnectionPool(size int) *ConnectionPool { return &ConnectionPool{ available: make(chan *Connection, size), } } // initialize sets up the connection pool func (cp *ConnectionPool) initialize() { fmt.Println("Initializing connection pool...") poolSize := cap(cp.available) cp.connections = make([]*Connection, poolSize) // Create and connect all connections for i := 0; i < poolSize; i++ { conn := &Connection{ID: i + 1} if err := conn.Connect(); err != nil { cp.initErr = fmt.Errorf("failed to connect connection %d: %w", i+1, err) return } cp.connections[i] = conn cp.available <- conn } fmt.Printf("Connection pool initialized with %d connections\n", poolSize) } // GetConnection gets a connection from the pool func (cp *ConnectionPool) GetConnection() (*Connection, error) { cp.once.Do(cp.initialize) if cp.initErr != nil { return nil, cp.initErr } select { case conn := <-cp.available: return conn, nil case <-time.After(5 * time.Second): return nil, fmt.Errorf("timeout waiting for connection") } } // ReturnConnection returns a connection to the pool func (cp *ConnectionPool) ReturnConnection(conn *Connection) { select { case cp.available <- conn: default: // Pool is full, close the connection conn.Close() } } // Close closes all connections in the pool func (cp *ConnectionPool) Close() error { close(cp.available) for _, conn := range cp.connections { if conn != nil { conn.Close() } } return nil } func main() { pool := NewConnectionPool(3) defer pool.Close() var wg sync.WaitGroup // Multiple goroutines using the connection pool for i := 0; i < 5; i++ { wg.Add(1) go func(id int) { defer wg.Done() conn, err := pool.GetConnection() if err != nil { fmt.Printf("Worker %d: Failed to get connection: %v\n", id, err) return } fmt.Printf("Worker %d: Got connection %d\n", id, conn.ID) // Simulate work time.Sleep(200 * time.Millisecond) pool.ReturnConnection(conn) fmt.Printf("Worker %d: Returned connection %d\n", id, conn.ID) }(i) } wg.Wait() } Advanced Once Patterns 1. Once with Error Handling package main import ( "fmt" "sync" ) // OnceWithError provides Once functionality with error handling type OnceWithError struct { once sync.Once err error } // Do executes the function once and stores any error func (o *OnceWithError) Do(f func() error) error { o.once.Do(func() { o.err = f() }) return o.err } // ExpensiveResource represents a resource that's expensive to initialize type ExpensiveResource struct { Data string } var ( resource *ExpensiveResource resourceOnce OnceWithError ) // initResource initializes the expensive resource func initResource() error { fmt.Println("Initializing expensive resource...") // Simulate potential failure if false { // Change to true to simulate error return fmt.Errorf("failed to initialize resource") } resource = &ExpensiveResource{ Data: "Important data", } fmt.Println("Resource initialized successfully!") return nil } // GetResource returns the resource, initializing it once if needed func GetResource() (*ExpensiveResource, error) { err := resourceOnce.Do(initResource) if err != nil { return nil, err } return resource, nil } func main() { var wg sync.WaitGroup for i := 0; i < 3; i++ { wg.Add(1) go func(id int) { defer wg.Done() resource, err := GetResource() if err != nil { fmt.Printf("Goroutine %d: Error: %v\n", id, err) return } fmt.Printf("Goroutine %d: Got resource: %s\n", id, resource.Data) }(i) } wg.Wait() } 2. Resettable Once package main import ( "fmt" "sync" "sync/atomic" ) // ResettableOnce allows resetting the once behavior type ResettableOnce struct { mu sync.Mutex done uint32 } // Do executes the function once func (ro *ResettableOnce) Do(f func()) { if atomic.LoadUint32(&ro.done) == 0 { ro.doSlow(f) } } func (ro *ResettableOnce) doSlow(f func()) { ro.mu.Lock() defer ro.mu.Unlock() if ro.done == 0 { defer atomic.StoreUint32(&ro.done, 1) f() } } // Reset allows the once to be used again func (ro *ResettableOnce) Reset() { ro.mu.Lock() defer ro.mu.Unlock() atomic.StoreUint32(&ro.done, 0) } // IsDone returns true if the function has been executed func (ro *ResettableOnce) IsDone() bool { return atomic.LoadUint32(&ro.done) == 1 } func main() { var once ResettableOnce counter := 0 task := func() { counter++ fmt.Printf("Task executed, counter: %d\n", counter) } // First round fmt.Println("First round:") for i := 0; i < 3; i++ { once.Do(task) } fmt.Printf("Done: %v\n", once.IsDone()) // Reset and second round fmt.Println("\nAfter reset:") once.Reset() fmt.Printf("Done: %v\n", once.IsDone()) for i := 0; i < 3; i++ { once.Do(task) } } Best Practices Use for Initialization: Perfect for one-time setup operations Keep Functions Simple: The function passed to Do() should be straightforward Handle Errors Separately: Use wrapper types for error handling Avoid Side Effects: Be careful with functions that have external side effects Don’t Nest Once Calls: Avoid calling Do() from within another Do() Consider Alternatives: Use init() for package-level initialization when appropriate Common Pitfalls 1. Expecting Return Values // Bad: Once.Do doesn't support return values var once sync.Once var result string func badExample() string { once.Do(func() { // Can't return from here result = "computed value" }) return result // This works but is not ideal } // Good: Use a wrapper or store results in accessible variables type OnceResult struct { once sync.Once result string err error } func (or *OnceResult) Get() (string, error) { or.once.Do(func() { or.result, or.err = computeValue() }) return or.result, or.err } 2. Panic in Once Function // Bad: Panic prevents future calls var once sync.Once func badOnceFunc() { once.Do(func() { panic("something went wrong") // Once will never execute again }) } // Good: Handle panics appropriately func goodOnceFunc() { once.Do(func() { defer func() { if r := recover(); r != nil { // Handle panic appropriately fmt.Printf("Recovered from panic: %v\n", r) } }() // risky operation }) } Testing Once Patterns package main import ( "sync" "testing" ) func TestOnceExecution(t *testing.T) { var once sync.Once counter := 0 var wg sync.WaitGroup // Start multiple goroutines for i := 0; i < 10; i++ { wg.Add(1) go func() { defer wg.Done() once.Do(func() { counter++ }) }() } wg.Wait() if counter != 1 { t.Errorf("Expected counter to be 1, got %d", counter) } } func TestOnceWithError(t *testing.T) { var onceErr OnceWithError callCount := 0 // First call with error err1 := onceErr.Do(func() error { callCount++ return fmt.Errorf("test error") }) // Second call should return same error without executing function err2 := onceErr.Do(func() error { callCount++ return nil }) if callCount != 1 { t.Errorf("Expected function to be called once, got %d", callCount) } if err1 == nil || err2 == nil { t.Error("Expected both calls to return error") } if err1.Error() != err2.Error() { t.Error("Expected same error from both calls") } } The Once pattern is essential for thread-safe initialization in Go. It ensures that expensive or critical setup operations happen exactly once, making it perfect for singletons, configuration loading, and resource initialization in concurrent applications. ...

From Object-Oriented to Data-Oriented Traditional object-oriented programming (OOP) encourages you to model game entities as objects with inheritance hierarchies. While intuitive, this approach leads to poor cache locality, rigid hierarchies, and performance bottlenecks. Data-oriented design, particularly the Entity Component System (ECS) pattern, flips this on its head. With Go 1.18+ generics, we can now build type-safe ECS architectures that deliver both performance and flexibility. Let me show you how. The OOP Problem Here’s the typical OOP approach to game entities: ...

Go Concurrency Patterns Series: ← Select Statement | Series Overview | Fan-Out/Fan-In → What is the Pipeline Pattern? The Pipeline pattern is a powerful way to structure concurrent data processing by breaking work into stages connected by channels. Each stage runs in its own goroutine, receives data from an input channel, processes it, and sends results to an output channel. This creates a chain of processing stages that can run concurrently, dramatically improving throughput. ...

Go Concurrency Patterns Series: ← Worker Pool | Series Overview | WaitGroup Pattern → What are Mutex Patterns? Mutex (mutual exclusion) patterns are essential for protecting shared resources in concurrent programs. Go provides sync.Mutex and sync.RWMutex for controlling access to critical sections, ensuring data consistency and preventing race conditions. Key Types: Mutex: Exclusive access (one goroutine at a time) RWMutex: Reader-writer locks (multiple readers OR one writer) Lock-free: Atomic operations without explicit locks Real-World Use Cases Shared Counters: Statistics, metrics, rate limiting Cache Systems: Thread-safe caching with read/write operations Configuration Management: Safe updates to application config Connection Pools: Managing database/HTTP connection pools Resource Allocation: Tracking and managing limited resources State Machines: Protecting state transitions Basic Mutex Usage package main import ( "fmt" "sync" "time" ) // Counter demonstrates basic mutex usage type Counter struct { mu sync.Mutex value int } // Increment safely increments the counter func (c *Counter) Increment() { c.mu.Lock() defer c.mu.Unlock() c.value++ } // Decrement safely decrements the counter func (c *Counter) Decrement() { c.mu.Lock() defer c.mu.Unlock() c.value-- } // Value safely returns the current value func (c *Counter) Value() int { c.mu.Lock() defer c.mu.Unlock() return c.value } // Add safely adds a value to the counter func (c *Counter) Add(delta int) { c.mu.Lock() defer c.mu.Unlock() c.value += delta } func main() { counter := &Counter{} var wg sync.WaitGroup // Start multiple goroutines incrementing the counter for i := 0; i < 10; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 100; j++ { counter.Increment() } fmt.Printf("Goroutine %d finished\n", id) }(i) } // Start some goroutines decrementing for i := 0; i < 3; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 50; j++ { counter.Decrement() } fmt.Printf("Decrementer %d finished\n", id) }(i) } wg.Wait() fmt.Printf("Final counter value: %d\n", counter.Value()) // Expected: (10 * 100) - (3 * 50) = 1000 - 150 = 850 } RWMutex for Read-Heavy Workloads package main import ( "fmt" "math/rand" "sync" "time" ) // Cache demonstrates RWMutex usage for read-heavy scenarios type Cache struct { mu sync.RWMutex data map[string]interface{} } // NewCache creates a new cache func NewCache() *Cache { return &Cache{ data: make(map[string]interface{}), } } // Get retrieves a value (read operation) func (c *Cache) Get(key string) (interface{}, bool) { c.mu.RLock() defer c.mu.RUnlock() value, exists := c.data[key] return value, exists } // Set stores a value (write operation) func (c *Cache) Set(key string, value interface{}) { c.mu.Lock() defer c.mu.Unlock() c.data[key] = value } // Delete removes a value (write operation) func (c *Cache) Delete(key string) { c.mu.Lock() defer c.mu.Unlock() delete(c.data, key) } // Keys returns all keys (read operation) func (c *Cache) Keys() []string { c.mu.RLock() defer c.mu.RUnlock() keys := make([]string, 0, len(c.data)) for key := range c.data { keys = append(keys, key) } return keys } // Size returns the number of items (read operation) func (c *Cache) Size() int { c.mu.RLock() defer c.mu.RUnlock() return len(c.data) } // Clear removes all items (write operation) func (c *Cache) Clear() { c.mu.Lock() defer c.mu.Unlock() c.data = make(map[string]interface{}) } func main() { cache := NewCache() var wg sync.WaitGroup // Writers (fewer, less frequent) for i := 0; i < 3; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 50; j++ { key := fmt.Sprintf("key-%d-%d", id, j) cache.Set(key, fmt.Sprintf("value-%d-%d", id, j)) time.Sleep(10 * time.Millisecond) } }(i) } // Readers (many, frequent) for i := 0; i < 10; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 100; j++ { // Try to read random keys key := fmt.Sprintf("key-%d-%d", rand.Intn(3), rand.Intn(50)) if value, exists := cache.Get(key); exists { fmt.Printf("Reader %d found %s: %v\n", id, key, value) } time.Sleep(5 * time.Millisecond) } }(i) } // Size checker wg.Add(1) go func() { defer wg.Done() for i := 0; i < 20; i++ { size := cache.Size() fmt.Printf("Cache size: %d\n", size) time.Sleep(100 * time.Millisecond) } }() wg.Wait() fmt.Printf("Final cache size: %d\n", cache.Size()) } Advanced Mutex Patterns 1. Conditional Variables Pattern package main import ( "fmt" "sync" "time" ) // Buffer demonstrates conditional variables with mutex type Buffer struct { mu sync.Mutex notEmpty *sync.Cond notFull *sync.Cond items []interface{} capacity int } // NewBuffer creates a new bounded buffer func NewBuffer(capacity int) *Buffer { b := &Buffer{ items: make([]interface{}, 0, capacity), capacity: capacity, } b.notEmpty = sync.NewCond(&b.mu) b.notFull = sync.NewCond(&b.mu) return b } // Put adds an item to the buffer (blocks if full) func (b *Buffer) Put(item interface{}) { b.mu.Lock() defer b.mu.Unlock() // Wait while buffer is full for len(b.items) == b.capacity { b.notFull.Wait() } b.items = append(b.items, item) fmt.Printf("Put item: %v (buffer size: %d)\n", item, len(b.items)) // Signal that buffer is not empty b.notEmpty.Signal() } // Get removes an item from the buffer (blocks if empty) func (b *Buffer) Get() interface{} { b.mu.Lock() defer b.mu.Unlock() // Wait while buffer is empty for len(b.items) == 0 { b.notEmpty.Wait() } item := b.items[0] b.items = b.items[1:] fmt.Printf("Got item: %v (buffer size: %d)\n", item, len(b.items)) // Signal that buffer is not full b.notFull.Signal() return item } // Size returns current buffer size func (b *Buffer) Size() int { b.mu.Lock() defer b.mu.Unlock() return len(b.items) } func main() { buffer := NewBuffer(3) var wg sync.WaitGroup // Producers for i := 0; i < 2; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 5; j++ { item := fmt.Sprintf("item-%d-%d", id, j) buffer.Put(item) time.Sleep(200 * time.Millisecond) } }(i) } // Consumers for i := 0; i < 2; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 5; j++ { item := buffer.Get() fmt.Printf("Consumer %d processed: %v\n", id, item) time.Sleep(300 * time.Millisecond) } }(i) } wg.Wait() } 2. Lock-Free Patterns with Atomic Operations package main import ( "fmt" "sync" "sync/atomic" "time" ) // AtomicCounter demonstrates lock-free counter type AtomicCounter struct { value int64 } // Increment atomically increments the counter func (ac *AtomicCounter) Increment() int64 { return atomic.AddInt64(&ac.value, 1) } // Decrement atomically decrements the counter func (ac *AtomicCounter) Decrement() int64 { return atomic.AddInt64(&ac.value, -1) } // Value atomically reads the current value func (ac *AtomicCounter) Value() int64 { return atomic.LoadInt64(&ac.value) } // CompareAndSwap atomically compares and swaps func (ac *AtomicCounter) CompareAndSwap(old, new int64) bool { return atomic.CompareAndSwapInt64(&ac.value, old, new) } // AtomicFlag demonstrates atomic boolean operations type AtomicFlag struct { flag int32 } // Set atomically sets the flag to true func (af *AtomicFlag) Set() { atomic.StoreInt32(&af.flag, 1) } // Clear atomically sets the flag to false func (af *AtomicFlag) Clear() { atomic.StoreInt32(&af.flag, 0) } // IsSet atomically checks if flag is set func (af *AtomicFlag) IsSet() bool { return atomic.LoadInt32(&af.flag) == 1 } // TestAndSet atomically tests and sets the flag func (af *AtomicFlag) TestAndSet() bool { return atomic.SwapInt32(&af.flag, 1) == 1 } func main() { counter := &AtomicCounter{} flag := &AtomicFlag{} var wg sync.WaitGroup // Test atomic counter fmt.Println("Testing atomic counter...") for i := 0; i < 10; i++ { wg.Add(1) go func(id int) { defer wg.Done() for j := 0; j < 1000; j++ { counter.Increment() } }(i) } wg.Wait() fmt.Printf("Final counter value: %d\n", counter.Value()) // Test atomic flag fmt.Println("\nTesting atomic flag...") // Multiple goroutines trying to set flag for i := 0; i < 5; i++ { wg.Add(1) go func(id int) { defer wg.Done() if !flag.TestAndSet() { fmt.Printf("Goroutine %d acquired the flag\n", id) time.Sleep(100 * time.Millisecond) flag.Clear() fmt.Printf("Goroutine %d released the flag\n", id) } else { fmt.Printf("Goroutine %d failed to acquire flag\n", id) } }(i) } wg.Wait() } 3. Resource Pool Pattern package main import ( "errors" "fmt" "sync" "time" ) // Resource represents a limited resource type Resource struct { ID int Data string } // ResourcePool manages a pool of limited resources type ResourcePool struct { mu sync.Mutex resources []*Resource available chan *Resource maxSize int created int } // NewResourcePool creates a new resource pool func NewResourcePool(maxSize int) *ResourcePool { return &ResourcePool{ resources: make([]*Resource, 0, maxSize), available: make(chan *Resource, maxSize), maxSize: maxSize, } } // createResource creates a new resource func (rp *ResourcePool) createResource() *Resource { rp.mu.Lock() defer rp.mu.Unlock() if rp.created >= rp.maxSize { return nil } rp.created++ resource := &Resource{ ID: rp.created, Data: fmt.Sprintf("Resource-%d", rp.created), } fmt.Printf("Created resource %d\n", resource.ID) return resource } // Acquire gets a resource from the pool func (rp *ResourcePool) Acquire() (*Resource, error) { select { case resource := <-rp.available: fmt.Printf("Acquired existing resource %d\n", resource.ID) return resource, nil default: // No available resource, try to create one if resource := rp.createResource(); resource != nil { return resource, nil } // Pool is full, wait for available resource fmt.Println("Pool full, waiting for available resource...") select { case resource := <-rp.available: fmt.Printf("Acquired resource %d after waiting\n", resource.ID) return resource, nil case <-time.After(5 * time.Second): return nil, errors.New("timeout waiting for resource") } } } // Release returns a resource to the pool func (rp *ResourcePool) Release(resource *Resource) { select { case rp.available <- resource: fmt.Printf("Released resource %d\n", resource.ID) default: // Channel full, resource will be garbage collected fmt.Printf("Pool full, discarding resource %d\n", resource.ID) } } // Size returns current pool statistics func (rp *ResourcePool) Size() (available, created int) { rp.mu.Lock() defer rp.mu.Unlock() return len(rp.available), rp.created } func main() { pool := NewResourcePool(3) var wg sync.WaitGroup // Multiple goroutines using resources for i := 0; i < 5; i++ { wg.Add(1) go func(id int) { defer wg.Done() resource, err := pool.Acquire() if err != nil { fmt.Printf("Worker %d failed to acquire resource: %v\n", id, err) return } fmt.Printf("Worker %d using resource %d\n", id, resource.ID) // Simulate work time.Sleep(time.Duration(200+id*100) * time.Millisecond) pool.Release(resource) fmt.Printf("Worker %d finished\n", id) }(i) } wg.Wait() available, created := pool.Size() fmt.Printf("Final pool state - Available: %d, Created: %d\n", available, created) } Best Practices Always Use defer: Ensure locks are released even if panic occurs Keep Critical Sections Small: Minimize time holding locks Avoid Nested Locks: Prevent deadlocks by avoiding lock hierarchies Use RWMutex for Read-Heavy: Better performance for read-heavy workloads Consider Lock-Free: Use atomic operations when possible Document Lock Order: If multiple locks needed, establish clear ordering Prefer Channels: Use channels for communication, locks for shared state Common Pitfalls 1. Deadlocks // Bad: Potential deadlock with nested locks type BadAccount struct { mu sync.Mutex balance int } func (a *BadAccount) Transfer(to *BadAccount, amount int) { a.mu.Lock() defer a.mu.Unlock() to.mu.Lock() // Potential deadlock if called concurrently defer to.mu.Unlock() a.balance -= amount to.balance += amount } // Good: Ordered locking to prevent deadlock func (a *BadAccount) SafeTransfer(to *BadAccount, amount int) { // Always acquire locks in consistent order first, second := a, to if a.ID > to.ID { first, second = to, a } first.mu.Lock() defer first.mu.Unlock() second.mu.Lock() defer second.mu.Unlock() a.balance -= amount to.balance += amount } 2. Race Conditions // Bad: Race condition type BadCounter struct { mu sync.Mutex value int } func (c *BadCounter) IncrementIfEven() { if c.value%2 == 0 { // Race: value might change between check and increment c.mu.Lock() c.value++ c.mu.Unlock() } } // Good: Atomic check and update func (c *BadCounter) SafeIncrementIfEven() { c.mu.Lock() defer c.mu.Unlock() if c.value%2 == 0 { c.value++ } } Testing Concurrent Code package main import ( "sync" "testing" ) func TestCounter(t *testing.T) { counter := &Counter{} var wg sync.WaitGroup goroutines := 100 increments := 1000 for i := 0; i < goroutines; i++ { wg.Add(1) go func() { defer wg.Done() for j := 0; j < increments; j++ { counter.Increment() } }() } wg.Wait() expected := goroutines * increments if counter.Value() != expected { t.Errorf("Expected %d, got %d", expected, counter.Value()) } } // Run with: go test -race func TestCounterRace(t *testing.T) { counter := &Counter{} go func() { for i := 0; i < 1000; i++ { counter.Increment() } }() go func() { for i := 0; i < 1000; i++ { _ = counter.Value() } }() } Mutex patterns are fundamental for building safe concurrent applications in Go. Choose the right synchronization primitive based on your access patterns: use sync.Mutex for exclusive access, sync.RWMutex for read-heavy workloads, and atomic operations for simple lock-free scenarios. ...

Go Concurrency Patterns Series: ← Go Generics Patterns | Series Overview What is Distributed Tracing? Distributed tracing tracks requests as they flow through microservices, providing visibility into performance bottlenecks, service dependencies, and error propagation in distributed systems. Key Concepts: Trace: End-to-end journey of a request across services Span: Single unit of work within a trace Context Propagation: Carrying trace information across boundaries Sampling: Controlling which traces to collect Why OpenTelemetry? OpenTelemetry (OTel) is the industry standard for observability: ...