Timeout

Building production-grade services requires more than just functionality—they need resilience, graceful degradation, and the ability to handle failures without crashing. In this post, we’ll build a robust logging service that demonstrates these principles using Go’s context package and proper error handling. The Problem Imagine your application sends logs to a remote logging service. What happens when: The logging service is slow or unresponsive? Network issues cause delays? The logging service crashes entirely? Without proper safeguards, your entire application could hang, crash, or become unresponsive just because logging failed. Logging should never bring down your application. ...

Go Concurrency Patterns Series: ← Once Pattern | Series Overview | Circuit Breaker → What is the Context Pattern? The Context pattern uses Go’s context package to carry cancellation signals, deadlines, timeouts, and request-scoped values across API boundaries and between goroutines. It’s essential for building responsive, cancellable operations and managing request lifecycles. Key Features: Cancellation: Signal when operations should stop Timeouts: Automatically cancel after a duration Deadlines: Cancel at a specific time Values: Carry request-scoped data Real-World Use Cases HTTP Servers: Request cancellation and timeouts Database Operations: Query timeouts and cancellation API Calls: External service timeouts Background Jobs: Graceful shutdown Microservices: Request tracing and correlation IDs File Operations: Long-running I/O with cancellation Basic Context Usage package main import ( "context" "fmt" "math/rand" "time" ) // simulateWork simulates a long-running operation func simulateWork(ctx context.Context, name string, duration time.Duration) error { fmt.Printf("%s: Starting work (expected duration: %v)\n", name, duration) select { case <-time.After(duration): fmt.Printf("%s: Work completed successfully\n", name) return nil case <-ctx.Done(): fmt.Printf("%s: Work cancelled: %v\n", name, ctx.Err()) return ctx.Err() } } func main() { // Example 1: Context with timeout fmt.Println("=== Context with Timeout ===") ctx1, cancel1 := context.WithTimeout(context.Background(), 2*time.Second) defer cancel1() err := simulateWork(ctx1, "Task1", 1*time.Second) // Should complete if err != nil { fmt.Printf("Task1 error: %v\n", err) } err = simulateWork(ctx1, "Task2", 3*time.Second) // Should timeout if err != nil { fmt.Printf("Task2 error: %v\n", err) } // Example 2: Manual cancellation fmt.Println("\n=== Manual Cancellation ===") ctx2, cancel2 := context.WithCancel(context.Background()) go func() { time.Sleep(1 * time.Second) fmt.Println("Cancelling context...") cancel2() }() err = simulateWork(ctx2, "Task3", 3*time.Second) // Should be cancelled if err != nil { fmt.Printf("Task3 error: %v\n", err) } // Example 3: Context with deadline fmt.Println("\n=== Context with Deadline ===") deadline := time.Now().Add(1500 * time.Millisecond) ctx3, cancel3 := context.WithDeadline(context.Background(), deadline) defer cancel3() err = simulateWork(ctx3, "Task4", 2*time.Second) // Should hit deadline if err != nil { fmt.Printf("Task4 error: %v\n", err) } } Context with Values package main import ( "context" "fmt" "log" "net/http" "time" ) // Key types for context values type contextKey string const ( RequestIDKey contextKey = "requestID" UserIDKey contextKey = "userID" TraceIDKey contextKey = "traceID" ) // RequestInfo holds request-scoped information type RequestInfo struct { RequestID string UserID string TraceID string StartTime time.Time } // withRequestInfo adds request information to context func withRequestInfo(ctx context.Context, info RequestInfo) context.Context { ctx = context.WithValue(ctx, RequestIDKey, info.RequestID) ctx = context.WithValue(ctx, UserIDKey, info.UserID) ctx = context.WithValue(ctx, TraceIDKey, info.TraceID) return ctx } // getRequestID extracts request ID from context func getRequestID(ctx context.Context) string { if id, ok := ctx.Value(RequestIDKey).(string); ok { return id } return "unknown" } // getUserID extracts user ID from context func getUserID(ctx context.Context) string { if id, ok := ctx.Value(UserIDKey).(string); ok { return id } return "anonymous" } // getTraceID extracts trace ID from context func getTraceID(ctx context.Context) string { if id, ok := ctx.Value(TraceIDKey).(string); ok { return id } return "no-trace" } // logWithContext logs with context information func logWithContext(ctx context.Context, message string) { requestID := getRequestID(ctx) userID := getUserID(ctx) traceID := getTraceID(ctx) fmt.Printf("[%s][%s][%s] %s\n", requestID, userID, traceID, message) } // businessLogic simulates business logic that uses context func businessLogic(ctx context.Context) error { logWithContext(ctx, "Starting business logic") // Simulate some work select { case <-time.After(500 * time.Millisecond): logWithContext(ctx, "Business logic completed") return nil case <-ctx.Done(): logWithContext(ctx, "Business logic cancelled") return ctx.Err() } } // databaseOperation simulates a database operation func databaseOperation(ctx context.Context, query string) error { logWithContext(ctx, fmt.Sprintf("Executing query: %s", query)) select { case <-time.After(200 * time.Millisecond): logWithContext(ctx, "Database operation completed") return nil case <-ctx.Done(): logWithContext(ctx, "Database operation cancelled") return ctx.Err() } } // externalAPICall simulates calling an external API func externalAPICall(ctx context.Context, endpoint string) error { logWithContext(ctx, fmt.Sprintf("Calling external API: %s", endpoint)) select { case <-time.After(300 * time.Millisecond): logWithContext(ctx, "External API call completed") return nil case <-ctx.Done(): logWithContext(ctx, "External API call cancelled") return ctx.Err() } } // handleRequest simulates handling an HTTP request func handleRequest(ctx context.Context) error { logWithContext(ctx, "Handling request") // Perform multiple operations if err := databaseOperation(ctx, "SELECT * FROM users"); err != nil { return err } if err := externalAPICall(ctx, "/api/v1/data"); err != nil { return err } if err := businessLogic(ctx); err != nil { return err } logWithContext(ctx, "Request handled successfully") return nil } func main() { // Simulate incoming request requestInfo := RequestInfo{ RequestID: "req-12345", UserID: "user-67890", TraceID: "trace-abcdef", StartTime: time.Now(), } // Create context with timeout and request info ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second) defer cancel() ctx = withRequestInfo(ctx, requestInfo) // Handle the request if err := handleRequest(ctx); err != nil { logWithContext(ctx, fmt.Sprintf("Request failed: %v", err)) } // Example with early cancellation fmt.Println("\n=== Early Cancellation Example ===") ctx2, cancel2 := context.WithTimeout(context.Background(), 2*time.Second) requestInfo2 := RequestInfo{ RequestID: "req-54321", UserID: "user-09876", TraceID: "trace-fedcba", StartTime: time.Now(), } ctx2 = withRequestInfo(ctx2, requestInfo2) // Cancel after 800ms go func() { time.Sleep(800 * time.Millisecond) logWithContext(ctx2, "Cancelling request early") cancel2() }() if err := handleRequest(ctx2); err != nil { logWithContext(ctx2, fmt.Sprintf("Request failed: %v", err)) } } HTTP Server with Context package main import ( "context" "encoding/json" "fmt" "log" "math/rand" "net/http" "strconv" "time" ) // Response represents an API response type Response struct { Message string `json:"message"` RequestID string `json:"request_id"` Duration time.Duration `json:"duration"` Data interface{} `json:"data,omitempty"` } // middleware adds request ID and timeout to context func middleware(next http.HandlerFunc) http.HandlerFunc { return func(w http.ResponseWriter, r *http.Request) { // Generate request ID requestID := fmt.Sprintf("req-%d", time.Now().UnixNano()) // Get timeout from query parameter (default 5 seconds) timeoutStr := r.URL.Query().Get("timeout") timeout := 5 * time.Second if timeoutStr != "" { if t, err := time.ParseDuration(timeoutStr); err == nil { timeout = t } } // Create context with timeout ctx, cancel := context.WithTimeout(r.Context(), timeout) defer cancel() // Add request ID to context ctx = context.WithValue(ctx, RequestIDKey, requestID) // Create new request with updated context r = r.WithContext(ctx) // Add request ID to response headers w.Header().Set("X-Request-ID", requestID) next(w, r) } } // simulateSlowOperation simulates a slow operation that respects context func simulateSlowOperation(ctx context.Context, duration time.Duration) (string, error) { select { case <-time.After(duration): return fmt.Sprintf("Operation completed after %v", duration), nil case <-ctx.Done(): return "", ctx.Err() } } // fastHandler handles requests quickly func fastHandler(w http.ResponseWriter, r *http.Request) { start := time.Now() ctx := r.Context() requestID := getRequestID(ctx) result, err := simulateSlowOperation(ctx, 100*time.Millisecond) duration := time.Since(start) response := Response{ RequestID: requestID, Duration: duration, } if err != nil { response.Message = "Request failed" w.WriteHeader(http.StatusRequestTimeout) } else { response.Message = "Success" response.Data = result } json.NewEncoder(w).Encode(response) } // slowHandler handles requests that might timeout func slowHandler(w http.ResponseWriter, r *http.Request) { start := time.Now() ctx := r.Context() requestID := getRequestID(ctx) // Random duration between 1-10 seconds duration := time.Duration(1+rand.Intn(10)) * time.Second result, err := simulateSlowOperation(ctx, duration) elapsed := time.Since(start) response := Response{ RequestID: requestID, Duration: elapsed, } if err != nil { response.Message = "Request timed out or cancelled" w.WriteHeader(http.StatusRequestTimeout) } else { response.Message = "Success" response.Data = result } json.NewEncoder(w).Encode(response) } // batchHandler processes multiple operations func batchHandler(w http.ResponseWriter, r *http.Request) { start := time.Now() ctx := r.Context() requestID := getRequestID(ctx) // Get batch size from query parameter batchSizeStr := r.URL.Query().Get("size") batchSize := 3 if batchSizeStr != "" { if size, err := strconv.Atoi(batchSizeStr); err == nil && size > 0 { batchSize = size } } results := make([]string, 0, batchSize) // Process operations sequentially, checking context each time for i := 0; i < batchSize; i++ { select { case <-ctx.Done(): // Context cancelled, return partial results response := Response{ RequestID: requestID, Duration: time.Since(start), Message: fmt.Sprintf("Batch cancelled after %d/%d operations", i, batchSize), Data: results, } w.WriteHeader(http.StatusRequestTimeout) json.NewEncoder(w).Encode(response) return default: } result, err := simulateSlowOperation(ctx, 200*time.Millisecond) if err != nil { response := Response{ RequestID: requestID, Duration: time.Since(start), Message: fmt.Sprintf("Batch failed at operation %d: %v", i+1, err), Data: results, } w.WriteHeader(http.StatusRequestTimeout) json.NewEncoder(w).Encode(response) return } results = append(results, fmt.Sprintf("Op%d: %s", i+1, result)) } response := Response{ RequestID: requestID, Duration: time.Since(start), Message: "Batch completed successfully", Data: results, } json.NewEncoder(w).Encode(response) } func main() { http.HandleFunc("/fast", middleware(fastHandler)) http.HandleFunc("/slow", middleware(slowHandler)) http.HandleFunc("/batch", middleware(batchHandler)) fmt.Println("Server starting on :8080") fmt.Println("Endpoints:") fmt.Println(" GET /fast - Fast operation (100ms)") fmt.Println(" GET /slow - Slow operation (1-10s random)") fmt.Println(" GET /batch?size=N - Batch operations") fmt.Println(" Add ?timeout=5s to set custom timeout") log.Fatal(http.ListenAndServe(":8080", nil)) } Context Propagation in Goroutines package main import ( "context" "fmt" "sync" "time" ) // Worker represents a worker that processes tasks type Worker struct { ID int Name string } // ProcessTask processes a task with context func (w *Worker) ProcessTask(ctx context.Context, taskID int) error { requestID := getRequestID(ctx) fmt.Printf("Worker %d (%s) [%s]: Starting task %d\n", w.ID, w.Name, requestID, taskID) // Simulate work with multiple steps for step := 1; step <= 3; step++ { select { case <-time.After(200 * time.Millisecond): fmt.Printf("Worker %d (%s) [%s]: Task %d step %d completed\n", w.ID, w.Name, requestID, taskID, step) case <-ctx.Done(): fmt.Printf("Worker %d (%s) [%s]: Task %d cancelled at step %d: %v\n", w.ID, w.Name, requestID, taskID, step, ctx.Err()) return ctx.Err() } } fmt.Printf("Worker %d (%s) [%s]: Task %d completed successfully\n", w.ID, w.Name, requestID, taskID) return nil } // TaskManager manages task distribution type TaskManager struct { workers []Worker } // NewTaskManager creates a new task manager func NewTaskManager() *TaskManager { return &TaskManager{ workers: []Worker{ {ID: 1, Name: "Alice"}, {ID: 2, Name: "Bob"}, {ID: 3, Name: "Charlie"}, }, } } // ProcessTasksConcurrently processes tasks using multiple workers func (tm *TaskManager) ProcessTasksConcurrently(ctx context.Context, taskCount int) error { var wg sync.WaitGroup taskChan := make(chan int, taskCount) errorChan := make(chan error, len(tm.workers)) // Send tasks to channel go func() { defer close(taskChan) for i := 1; i <= taskCount; i++ { select { case taskChan <- i: case <-ctx.Done(): return } } }() // Start workers for _, worker := range tm.workers { wg.Add(1) go func(w Worker) { defer wg.Done() for { select { case taskID, ok := <-taskChan: if !ok { return // No more tasks } if err := w.ProcessTask(ctx, taskID); err != nil { select { case errorChan <- err: case <-ctx.Done(): } return } case <-ctx.Done(): return } } }(worker) } // Wait for completion or cancellation done := make(chan struct{}) go func() { wg.Wait() close(done) }() select { case <-done: close(errorChan) // Check for errors for err := range errorChan { if err != nil { return err } } return nil case <-ctx.Done(): return ctx.Err() } } func main() { manager := NewTaskManager() // Example 1: Normal completion fmt.Println("=== Normal Completion ===") ctx1, cancel1 := context.WithTimeout(context.Background(), 5*time.Second) ctx1 = context.WithValue(ctx1, RequestIDKey, "batch-001") defer cancel1() err := manager.ProcessTasksConcurrently(ctx1, 6) if err != nil { fmt.Printf("Batch processing failed: %v\n", err) } else { fmt.Println("Batch processing completed successfully") } time.Sleep(1 * time.Second) // Example 2: Timeout scenario fmt.Println("\n=== Timeout Scenario ===") ctx2, cancel2 := context.WithTimeout(context.Background(), 1*time.Second) ctx2 = context.WithValue(ctx2, RequestIDKey, "batch-002") defer cancel2() err = manager.ProcessTasksConcurrently(ctx2, 10) if err != nil { fmt.Printf("Batch processing failed: %v\n", err) } else { fmt.Println("Batch processing completed successfully") } time.Sleep(1 * time.Second) // Example 3: Manual cancellation fmt.Println("\n=== Manual Cancellation ===") ctx3, cancel3 := context.WithCancel(context.Background()) ctx3 = context.WithValue(ctx3, RequestIDKey, "batch-003") // Cancel after 800ms go func() { time.Sleep(800 * time.Millisecond) fmt.Println("Manually cancelling batch...") cancel3() }() err = manager.ProcessTasksConcurrently(ctx3, 8) if err != nil { fmt.Printf("Batch processing failed: %v\n", err) } else { fmt.Println("Batch processing completed successfully") } } Best Practices Always Accept Context: Functions that might block should accept context as first parameter Don’t Store Context: Pass context as parameter, don’t store in structs Use context.TODO(): When you don’t have context but need one Derive Contexts: Create child contexts from parent contexts Handle Cancellation: Always check ctx.Done() in long-running operations Limit Context Values: Use sparingly and for request-scoped data only Use Typed Keys: Define custom types for context keys to avoid collisions Common Pitfalls 1. Ignoring Context Cancellation // Bad: Ignoring context cancellation func badOperation(ctx context.Context) error { for i := 0; i < 1000; i++ { // Long operation without checking context time.Sleep(10 * time.Millisecond) // Process item i } return nil } // Good: Checking context regularly func goodOperation(ctx context.Context) error { for i := 0; i < 1000; i++ { select { case <-ctx.Done(): return ctx.Err() default: } time.Sleep(10 * time.Millisecond) // Process item i } return nil } 2. Using Context for Optional Parameters // Bad: Using context for optional parameters func badFunction(ctx context.Context) { if timeout, ok := ctx.Value("timeout").(time.Duration); ok { // Use timeout } } // Good: Use function parameters for optional values func goodFunction(ctx context.Context, timeout time.Duration) { // Use timeout parameter } The Context pattern is fundamental for building robust, cancellable operations in Go. It enables graceful handling of timeouts, cancellations, and request-scoped data, making your applications more responsive and resource-efficient. ...