Fault-Tolerance

The Bully Election Algorithm The Bully Algorithm, proposed by Hector Garcia-Molina in 1982, is a classic leader election algorithm for distributed systems. It’s called “bully” because the highest-numbered process always wins and “bullies” the others into accepting it as leader. The Scenario A distributed system needs a coordinator: N nodes in a network Each node has a unique ID (priority) One node must be elected as leader When the leader fails, a new leader must be elected Rule: The node with the highest ID wins The protocol: ...

The Byzantine Generals Problem The Byzantine Generals Problem, proposed by Leslie Lamport, Robert Shostak, and Marshall Pease in 1982, is one of the most important problems in distributed systems. It addresses the challenge of achieving consensus when some participants may be faulty or malicious. The Scenario Byzantine army divisions surround a city: N generals command their divisions They must coordinate: attack or retreat They communicate via messengers Some generals are traitors who send conflicting messages Goal: All loyal generals must agree on the same plan The challenge: ...

Go Concurrency Patterns Series: ← Context Pattern | Series Overview | Rate Limiter → What is the Circuit Breaker Pattern? The Circuit Breaker pattern prevents cascading failures in distributed systems by monitoring for failures and temporarily stopping calls to failing services. Like an electrical circuit breaker, it “trips” when failures exceed a threshold, giving the failing service time to recover. States: Closed: Normal operation, requests pass through Open: Failing fast, requests are rejected immediately Half-Open: Testing if service has recovered Real-World Use Cases Microservices: Prevent cascade failures between services Database Connections: Handle database outages gracefully External APIs: Deal with third-party service failures Payment Processing: Handle payment gateway issues File Systems: Manage disk I/O failures Network Operations: Handle network partitions Basic Circuit Breaker Implementation package main import ( "context" "errors" "fmt" "sync" "time" ) // State represents the circuit breaker state type State int const ( StateClosed State = iota StateOpen StateHalfOpen ) func (s State) String() string { switch s { case StateClosed: return "CLOSED" case StateOpen: return "OPEN" case StateHalfOpen: return "HALF_OPEN" default: return "UNKNOWN" } } // CircuitBreaker implements the circuit breaker pattern type CircuitBreaker struct { mu sync.RWMutex state State failureCount int successCount int lastFailureTime time.Time nextAttemptTime time.Time // Configuration maxFailures int resetTimeout time.Duration halfOpenMaxCalls int } // Config holds circuit breaker configuration type Config struct { MaxFailures int // Number of failures before opening ResetTimeout time.Duration // Time to wait before trying half-open HalfOpenMaxCalls int // Max calls allowed in half-open state } // NewCircuitBreaker creates a new circuit breaker func NewCircuitBreaker(config Config) *CircuitBreaker { return &CircuitBreaker{ state: StateClosed, maxFailures: config.MaxFailures, resetTimeout: config.ResetTimeout, halfOpenMaxCalls: config.HalfOpenMaxCalls, } } // Execute runs the given function with circuit breaker protection func (cb *CircuitBreaker) Execute(fn func() error) error { if !cb.allowRequest() { return errors.New("circuit breaker is open") } err := fn() cb.recordResult(err) return err } // allowRequest determines if a request should be allowed func (cb *CircuitBreaker) allowRequest() bool { cb.mu.Lock() defer cb.mu.Unlock() now := time.Now() switch cb.state { case StateClosed: return true case StateOpen: if now.After(cb.nextAttemptTime) { cb.state = StateHalfOpen cb.successCount = 0 cb.failureCount = 0 fmt.Printf("Circuit breaker transitioning to HALF_OPEN\n") return true } return false case StateHalfOpen: return cb.successCount + cb.failureCount < cb.halfOpenMaxCalls default: return false } } // recordResult records the result of a function call func (cb *CircuitBreaker) recordResult(err error) { cb.mu.Lock() defer cb.mu.Unlock() if err != nil { cb.onFailure() } else { cb.onSuccess() } } // onFailure handles a failure func (cb *CircuitBreaker) onFailure() { cb.failureCount++ cb.lastFailureTime = time.Now() switch cb.state { case StateClosed: if cb.failureCount >= cb.maxFailures { cb.state = StateOpen cb.nextAttemptTime = time.Now().Add(cb.resetTimeout) fmt.Printf("Circuit breaker OPENED after %d failures\n", cb.failureCount) } case StateHalfOpen: cb.state = StateOpen cb.nextAttemptTime = time.Now().Add(cb.resetTimeout) fmt.Printf("Circuit breaker returned to OPEN from HALF_OPEN\n") } } // onSuccess handles a success func (cb *CircuitBreaker) onSuccess() { switch cb.state { case StateClosed: cb.failureCount = 0 case StateHalfOpen: cb.successCount++ if cb.successCount >= cb.halfOpenMaxCalls { cb.state = StateClosed cb.failureCount = 0 fmt.Printf("Circuit breaker CLOSED after successful recovery\n") } } } // GetState returns the current state func (cb *CircuitBreaker) GetState() State { cb.mu.RLock() defer cb.mu.RUnlock() return cb.state } // GetStats returns current statistics func (cb *CircuitBreaker) GetStats() (State, int, int) { cb.mu.RLock() defer cb.mu.RUnlock() return cb.state, cb.failureCount, cb.successCount } // simulateService simulates a service that might fail func simulateService(shouldFail bool, delay time.Duration) func() error { return func() error { time.Sleep(delay) if shouldFail { return errors.New("service failure") } return nil } } func main() { config := Config{ MaxFailures: 3, ResetTimeout: 2 * time.Second, HalfOpenMaxCalls: 2, } cb := NewCircuitBreaker(config) // Test scenario: failures followed by recovery scenarios := []struct { name string shouldFail bool delay time.Duration }{ {"Success 1", false, 100 * time.Millisecond}, {"Success 2", false, 100 * time.Millisecond}, {"Failure 1", true, 100 * time.Millisecond}, {"Failure 2", true, 100 * time.Millisecond}, {"Failure 3", true, 100 * time.Millisecond}, // Should open circuit {"Blocked 1", false, 100 * time.Millisecond}, // Should be blocked {"Blocked 2", false, 100 * time.Millisecond}, // Should be blocked } for i, scenario := range scenarios { fmt.Printf("\n--- Test %d: %s ---\n", i+1, scenario.name) err := cb.Execute(simulateService(scenario.shouldFail, scenario.delay)) state, failures, successes := cb.GetStats() if err != nil { fmt.Printf("Result: ERROR - %v\n", err) } else { fmt.Printf("Result: SUCCESS\n") } fmt.Printf("State: %s, Failures: %d, Successes: %d\n", state, failures, successes) time.Sleep(100 * time.Millisecond) } // Wait for reset timeout and test recovery fmt.Printf("\n--- Waiting for reset timeout (%v) ---\n", config.ResetTimeout) time.Sleep(config.ResetTimeout + 100*time.Millisecond) // Test recovery recoveryTests := []struct { name string shouldFail bool }{ {"Recovery 1", false}, // Should succeed and move to half-open {"Recovery 2", false}, // Should succeed and close circuit {"Success after recovery", false}, } for i, test := range recoveryTests { fmt.Printf("\n--- Recovery Test %d: %s ---\n", i+1, test.name) err := cb.Execute(simulateService(test.shouldFail, 100*time.Millisecond)) state, failures, successes := cb.GetStats() if err != nil { fmt.Printf("Result: ERROR - %v\n", err) } else { fmt.Printf("Result: SUCCESS\n") } fmt.Printf("State: %s, Failures: %d, Successes: %d\n", state, failures, successes) } } Advanced Circuit Breaker with Metrics package main import ( "context" "fmt" "sync" "sync/atomic" "time" ) // Metrics tracks circuit breaker statistics type Metrics struct { totalRequests int64 successfulCalls int64 failedCalls int64 rejectedCalls int64 timeouts int64 stateChanges int64 } // AdvancedCircuitBreaker with comprehensive metrics and monitoring type AdvancedCircuitBreaker struct { mu sync.RWMutex state State failureCount int successCount int lastFailureTime time.Time nextAttemptTime time.Time stateChangeTime time.Time // Configuration maxFailures int resetTimeout time.Duration halfOpenMaxCalls int callTimeout time.Duration // Metrics metrics *Metrics // Monitoring onStateChange func(from, to State) } // AdvancedConfig holds advanced circuit breaker configuration type AdvancedConfig struct { MaxFailures int ResetTimeout time.Duration HalfOpenMaxCalls int CallTimeout time.Duration OnStateChange func(from, to State) } // NewAdvancedCircuitBreaker creates a new advanced circuit breaker func NewAdvancedCircuitBreaker(config AdvancedConfig) *AdvancedCircuitBreaker { return &AdvancedCircuitBreaker{ state: StateClosed, maxFailures: config.MaxFailures, resetTimeout: config.ResetTimeout, halfOpenMaxCalls: config.HalfOpenMaxCalls, callTimeout: config.CallTimeout, metrics: &Metrics{}, onStateChange: config.OnStateChange, stateChangeTime: time.Now(), } } // ExecuteWithContext runs function with context and timeout func (acb *AdvancedCircuitBreaker) ExecuteWithContext(ctx context.Context, fn func(context.Context) error) error { atomic.AddInt64(&acb.metrics.totalRequests, 1) if !acb.allowRequest() { atomic.AddInt64(&acb.metrics.rejectedCalls, 1) return fmt.Errorf("circuit breaker is %s", acb.GetState()) } // Create context with timeout if specified if acb.callTimeout > 0 { var cancel context.CancelFunc ctx, cancel = context.WithTimeout(ctx, acb.callTimeout) defer cancel() } // Execute with timeout monitoring done := make(chan error, 1) go func() { done <- fn(ctx) }() select { case err := <-done: acb.recordResult(err) return err case <-ctx.Done(): atomic.AddInt64(&acb.metrics.timeouts, 1) acb.recordResult(ctx.Err()) return ctx.Err() } } // allowRequest determines if a request should be allowed func (acb *AdvancedCircuitBreaker) allowRequest() bool { acb.mu.Lock() defer acb.mu.Unlock() now := time.Now() switch acb.state { case StateClosed: return true case StateOpen: if now.After(acb.nextAttemptTime) { acb.changeState(StateHalfOpen) acb.successCount = 0 acb.failureCount = 0 return true } return false case StateHalfOpen: return acb.successCount + acb.failureCount < acb.halfOpenMaxCalls default: return false } } // recordResult records the result of a function call func (acb *AdvancedCircuitBreaker) recordResult(err error) { acb.mu.Lock() defer acb.mu.Unlock() if err != nil { atomic.AddInt64(&acb.metrics.failedCalls, 1) acb.onFailure() } else { atomic.AddInt64(&acb.metrics.successfulCalls, 1) acb.onSuccess() } } // changeState changes the circuit breaker state func (acb *AdvancedCircuitBreaker) changeState(newState State) { if acb.state != newState { oldState := acb.state acb.state = newState acb.stateChangeTime = time.Now() atomic.AddInt64(&acb.metrics.stateChanges, 1) if acb.onStateChange != nil { go acb.onStateChange(oldState, newState) } } } // onFailure handles a failure func (acb *AdvancedCircuitBreaker) onFailure() { acb.failureCount++ acb.lastFailureTime = time.Now() switch acb.state { case StateClosed: if acb.failureCount >= acb.maxFailures { acb.changeState(StateOpen) acb.nextAttemptTime = time.Now().Add(acb.resetTimeout) } case StateHalfOpen: acb.changeState(StateOpen) acb.nextAttemptTime = time.Now().Add(acb.resetTimeout) } } // onSuccess handles a success func (acb *AdvancedCircuitBreaker) onSuccess() { switch acb.state { case StateClosed: acb.failureCount = 0 case StateHalfOpen: acb.successCount++ if acb.successCount >= acb.halfOpenMaxCalls { acb.changeState(StateClosed) acb.failureCount = 0 } } } // GetMetrics returns current metrics func (acb *AdvancedCircuitBreaker) GetMetrics() Metrics { return Metrics{ totalRequests: atomic.LoadInt64(&acb.metrics.totalRequests), successfulCalls: atomic.LoadInt64(&acb.metrics.successfulCalls), failedCalls: atomic.LoadInt64(&acb.metrics.failedCalls), rejectedCalls: atomic.LoadInt64(&acb.metrics.rejectedCalls), timeouts: atomic.LoadInt64(&acb.metrics.timeouts), stateChanges: atomic.LoadInt64(&acb.metrics.stateChanges), } } // GetState returns current state func (acb *AdvancedCircuitBreaker) GetState() State { acb.mu.RLock() defer acb.mu.RUnlock() return acb.state } // HealthCheck returns health information func (acb *AdvancedCircuitBreaker) HealthCheck() map[string]interface{} { acb.mu.RLock() defer acb.mu.RUnlock() metrics := acb.GetMetrics() var successRate float64 if metrics.totalRequests > 0 { successRate = float64(metrics.successfulCalls) / float64(metrics.totalRequests) * 100 } return map[string]interface{}{ "state": acb.state.String(), "failure_count": acb.failureCount, "success_count": acb.successCount, "last_failure_time": acb.lastFailureTime, "state_change_time": acb.stateChangeTime, "next_attempt_time": acb.nextAttemptTime, "total_requests": metrics.totalRequests, "successful_calls": metrics.successfulCalls, "failed_calls": metrics.failedCalls, "rejected_calls": metrics.rejectedCalls, "timeouts": metrics.timeouts, "state_changes": metrics.stateChanges, "success_rate": fmt.Sprintf("%.2f%%", successRate), } } // Service simulation type ExternalService struct { failureRate float64 latency time.Duration } func (es *ExternalService) Call(ctx context.Context, data string) error { // Simulate latency select { case <-time.After(es.latency): case <-ctx.Done(): return ctx.Err() } // Simulate random failures if time.Now().UnixNano()%100 < int64(es.failureRate*100) { return fmt.Errorf("service failure for data: %s", data) } return nil } func main() { // Create service that fails 30% of the time service := &ExternalService{ failureRate: 0.3, latency: 100 * time.Millisecond, } config := AdvancedConfig{ MaxFailures: 3, ResetTimeout: 2 * time.Second, HalfOpenMaxCalls: 2, CallTimeout: 500 * time.Millisecond, OnStateChange: func(from, to State) { fmt.Printf(" Circuit breaker state changed: %s -> %s\n", from, to) }, } cb := NewAdvancedCircuitBreaker(config) // Monitor circuit breaker health go func() { ticker := time.NewTicker(1 * time.Second) defer ticker.Stop() for range ticker.C { health := cb.HealthCheck() fmt.Printf(" Health: State=%s, Success Rate=%s, Total=%d, Failed=%d, Rejected=%d\n", health["state"], health["success_rate"], health["total_requests"], health["failed_calls"], health["rejected_calls"]) } }() // Simulate load var wg sync.WaitGroup for i := 0; i < 50; i++ { wg.Add(1) go func(id int) { defer wg.Done() ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second) defer cancel() err := cb.ExecuteWithContext(ctx, func(ctx context.Context) error { return service.Call(ctx, fmt.Sprintf("request-%d", id)) }) if err != nil { fmt.Printf(" Request %d failed: %v\n", id, err) } else { fmt.Printf(" Request %d succeeded\n", id) } time.Sleep(200 * time.Millisecond) }(i) } wg.Wait() // Final health report fmt.Println("\n Final Health Report:") health := cb.HealthCheck() for key, value := range health { fmt.Printf(" %s: %v\n", key, value) } } HTTP Client with Circuit Breaker package main import ( "context" "encoding/json" "fmt" "io" "net/http" "time" ) // HTTPClient wraps http.Client with circuit breaker type HTTPClient struct { client *http.Client circuitBreaker *AdvancedCircuitBreaker } // NewHTTPClient creates a new HTTP client with circuit breaker func NewHTTPClient(timeout time.Duration, cbConfig AdvancedConfig) *HTTPClient { return &HTTPClient{ client: &http.Client{ Timeout: timeout, }, circuitBreaker: NewAdvancedCircuitBreaker(cbConfig), } } // Get performs a GET request with circuit breaker protection func (hc *HTTPClient) Get(ctx context.Context, url string) (*http.Response, error) { var resp *http.Response err := hc.circuitBreaker.ExecuteWithContext(ctx, func(ctx context.Context) error { req, err := http.NewRequestWithContext(ctx, "GET", url, nil) if err != nil { return err } var httpErr error resp, httpErr = hc.client.Do(req) if httpErr != nil { return httpErr } // Consider 5xx status codes as failures if resp.StatusCode >= 500 { resp.Body.Close() return fmt.Errorf("server error: %d", resp.StatusCode) } return nil }) return resp, err } // GetJSON performs a GET request and unmarshals JSON response func (hc *HTTPClient) GetJSON(ctx context.Context, url string, target interface{}) error { resp, err := hc.Get(ctx, url) if err != nil { return err } defer resp.Body.Close() body, err := io.ReadAll(resp.Body) if err != nil { return err } return json.Unmarshal(body, target) } // GetHealth returns circuit breaker health func (hc *HTTPClient) GetHealth() map[string]interface{} { return hc.circuitBreaker.HealthCheck() } // Example usage func main() { config := AdvancedConfig{ MaxFailures: 3, ResetTimeout: 5 * time.Second, HalfOpenMaxCalls: 2, CallTimeout: 2 * time.Second, OnStateChange: func(from, to State) { fmt.Printf(" HTTP Client circuit breaker: %s -> %s\n", from, to) }, } client := NewHTTPClient(3*time.Second, config) // Test URLs (some will fail) urls := []string{ "https://httpbin.org/status/200", // Success "https://httpbin.org/status/500", // Server error "https://httpbin.org/delay/1", // Success with delay "https://httpbin.org/status/503", // Server error "https://httpbin.org/status/500", // Server error "https://httpbin.org/status/502", // Server error (should open circuit) "https://httpbin.org/status/200", // Should be rejected "https://httpbin.org/status/200", // Should be rejected } for i, url := range urls { fmt.Printf("\n--- Request %d: %s ---\n", i+1, url) ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) resp, err := client.Get(ctx, url) if err != nil { fmt.Printf(" Error: %v\n", err) } else { fmt.Printf(" Success: %d %s\n", resp.StatusCode, resp.Status) resp.Body.Close() } cancel() // Show current health health := client.GetHealth() fmt.Printf("State: %s, Success Rate: %s\n", health["state"], health["success_rate"]) time.Sleep(1 * time.Second) } // Wait for circuit to potentially reset fmt.Println("\n--- Waiting for potential reset ---") time.Sleep(6 * time.Second) // Try again fmt.Println("\n--- Testing recovery ---") ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) defer cancel() resp, err := client.Get(ctx, "https://httpbin.org/status/200") if err != nil { fmt.Printf(" Recovery test failed: %v\n", err) } else { fmt.Printf(" Recovery test succeeded: %d %s\n", resp.StatusCode, resp.Status) resp.Body.Close() } // Final health report fmt.Println("\n Final Health Report:") health := client.GetHealth() for key, value := range health { fmt.Printf(" %s: %v\n", key, value) } } Best Practices Choose Appropriate Thresholds: Set failure thresholds based on service characteristics Monitor State Changes: Log state transitions for debugging Implement Fallbacks: Provide alternative responses when circuit is open Use Timeouts: Combine with timeouts to handle slow responses Gradual Recovery: Use half-open state to test service recovery Metrics Collection: Track success rates, response times, and state changes Configuration: Make thresholds configurable for different environments Common Pitfalls Too Sensitive: Setting thresholds too low causes unnecessary trips Too Tolerant: High thresholds don’t protect against cascading failures No Fallbacks: Not providing alternative responses when circuit is open Ignoring Context: Not respecting context cancellation in protected functions Poor Monitoring: Not tracking circuit breaker metrics and health The Circuit Breaker pattern is essential for building resilient distributed systems. It prevents cascading failures, provides fast failure responses, and allows services time to recover, making your applications more robust and reliable. ...

Go Concurrency Patterns Series: ← Semaphore Pattern | Series Overview What is the Actor Model? The Actor Model is a conceptual model for concurrent computation where “actors” are the fundamental units of computation. Each actor has its own isolated state, processes messages sequentially, and can create other actors, send messages, or change its behavior in response to messages. Key Principles: Isolated State: Each actor maintains its own private state Message Passing: Actors communicate only through asynchronous messages Sequential Processing: Each actor processes one message at a time Location Transparency: Actors can be local or remote Fault Tolerance: Actor failures are isolated and recoverable Real-World Use Cases Distributed Systems: Microservices communication Game Servers: Player state management IoT Systems: Device state and communication Financial Systems: Transaction processing Chat Applications: User session management Workflow Engines: Task orchestration Basic Actor Implementation package main import ( "context" "fmt" "sync" "time" ) // Message represents a message sent to an actor type Message interface{} // Actor represents the basic actor interface type Actor interface { Receive(message Message) Start(ctx context.Context) Stop() Send(message Message) GetID() string } // BaseActor provides basic actor functionality type BaseActor struct { id string mailbox chan Message quit chan struct{} wg sync.WaitGroup behavior func(Message) } // NewBaseActor creates a new base actor func NewBaseActor(id string, behavior func(Message)) *BaseActor { return &BaseActor{ id: id, mailbox: make(chan Message, 100), quit: make(chan struct{}), behavior: behavior, } } // GetID returns the actor ID func (ba *BaseActor) GetID() string { return ba.id } // Send sends a message to the actor func (ba *BaseActor) Send(message Message) { select { case ba.mailbox <- message: case <-ba.quit: fmt.Printf("Actor %s: Cannot send message, actor is stopped\n", ba.id) } } // Start starts the actor's message processing loop func (ba *BaseActor) Start(ctx context.Context) { ba.wg.Add(1) go func() { defer ba.wg.Done() fmt.Printf("Actor %s: Started\n", ba.id) for { select { case message := <-ba.mailbox: ba.Receive(message) case <-ba.quit: fmt.Printf("Actor %s: Stopped\n", ba.id) return case <-ctx.Done(): fmt.Printf("Actor %s: Context cancelled\n", ba.id) return } } }() } // Receive processes a received message func (ba *BaseActor) Receive(message Message) { if ba.behavior != nil { ba.behavior(message) } } // Stop stops the actor func (ba *BaseActor) Stop() { close(ba.quit) ba.wg.Wait() } // Common message types type StartMessage struct{} type StopMessage struct{} type PingMessage struct { Sender Actor } type PongMessage struct { Sender Actor } // CounterActor demonstrates a stateful actor type CounterActor struct { *BaseActor count int } // CounterMessage types type IncrementMessage struct{} type DecrementMessage struct{} type GetCountMessage struct { ResponseChan chan int } // NewCounterActor creates a new counter actor func NewCounterActor(id string) *CounterActor { ca := &CounterActor{ count: 0, } ca.BaseActor = NewBaseActor(id, ca.handleMessage) return ca } // handleMessage handles counter-specific messages func (ca *CounterActor) handleMessage(message Message) { switch msg := message.(type) { case IncrementMessage: ca.count++ fmt.Printf("Counter %s: Incremented to %d\n", ca.id, ca.count) case DecrementMessage: ca.count-- fmt.Printf("Counter %s: Decremented to %d\n", ca.id, ca.count) case GetCountMessage: fmt.Printf("Counter %s: Current count is %d\n", ca.id, ca.count) msg.ResponseChan <- ca.count case PingMessage: fmt.Printf("Counter %s: Received ping from %s\n", ca.id, msg.Sender.GetID()) msg.Sender.Send(PongMessage{Sender: ca}) default: fmt.Printf("Counter %s: Unknown message type: %T\n", ca.id, message) } } func main() { ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second) defer cancel() fmt.Println("=== Basic Actor Model Demo ===") // Create counter actors counter1 := NewCounterActor("counter-1") counter2 := NewCounterActor("counter-2") // Start actors counter1.Start(ctx) counter2.Start(ctx) defer counter1.Stop() defer counter2.Stop() // Send messages to actors counter1.Send(IncrementMessage{}) counter1.Send(IncrementMessage{}) counter1.Send(IncrementMessage{}) counter2.Send(IncrementMessage{}) counter2.Send(DecrementMessage{}) // Ping-pong between actors counter1.Send(PingMessage{Sender: counter2}) // Get current counts responseChan1 := make(chan int) responseChan2 := make(chan int) counter1.Send(GetCountMessage{ResponseChan: responseChan1}) counter2.Send(GetCountMessage{ResponseChan: responseChan2}) count1 := <-responseChan1 count2 := <-responseChan2 fmt.Printf("Final counts - Counter1: %d, Counter2: %d\n", count1, count2) time.Sleep(1 * time.Second) } Advanced Actor System with Supervision package main import ( "context" "fmt" "sync" "time" ) // ActorRef represents a reference to an actor type ActorRef struct { id string mailbox chan Message } // Send sends a message to the actor func (ref *ActorRef) Send(message Message) { select { case ref.mailbox <- message: default: fmt.Printf("ActorRef %s: Mailbox full, dropping message\n", ref.id) } } // GetID returns the actor ID func (ref *ActorRef) GetID() string { return ref.id } // ActorSystem manages actors and provides supervision type ActorSystem struct { mu sync.RWMutex actors map[string]*ManagedActor ctx context.Context cancel context.CancelFunc } // ManagedActor wraps an actor with management capabilities type ManagedActor struct { ref *ActorRef behavior ActorBehavior supervisor *ActorRef children map[string]*ActorRef mu sync.RWMutex restarts int maxRestarts int } // ActorBehavior defines how an actor processes messages type ActorBehavior func(ctx ActorContext, message Message) // ActorContext provides context for actor operations type ActorContext struct { Self *ActorRef System *ActorSystem Sender *ActorRef } // NewActorSystem creates a new actor system func NewActorSystem() *ActorSystem { ctx, cancel := context.WithCancel(context.Background()) return &ActorSystem{ actors: make(map[string]*ManagedActor), ctx: ctx, cancel: cancel, } } // ActorOf creates a new actor func (as *ActorSystem) ActorOf(id string, behavior ActorBehavior, supervisor *ActorRef) *ActorRef { as.mu.Lock() defer as.mu.Unlock() ref := &ActorRef{ id: id, mailbox: make(chan Message, 100), } actor := &ManagedActor{ ref: ref, behavior: behavior, supervisor: supervisor, children: make(map[string]*ActorRef), maxRestarts: 3, } as.actors[id] = actor // Start actor goroutine go as.runActor(actor) fmt.Printf("ActorSystem: Created actor %s\n", id) return ref } // runActor runs the actor's message processing loop func (as *ActorSystem) runActor(actor *ManagedActor) { defer func() { if r := recover(); r != nil { fmt.Printf("Actor %s: Panic recovered: %v\n", actor.ref.id, r) as.handleActorFailure(actor, fmt.Errorf("panic: %v", r)) } }() for { select { case message := <-actor.ref.mailbox: ctx := ActorContext{ Self: actor.ref, System: as, } actor.behavior(ctx, message) case <-as.ctx.Done(): fmt.Printf("Actor %s: System shutdown\n", actor.ref.id) return } } } // handleActorFailure handles actor failures and restarts func (as *ActorSystem) handleActorFailure(actor *ManagedActor, err error) { actor.mu.Lock() defer actor.mu.Unlock() actor.restarts++ fmt.Printf("Actor %s: Failed with error: %v (restart %d/%d)\n", actor.ref.id, err, actor.restarts, actor.maxRestarts) if actor.restarts <= actor.maxRestarts { // Restart the actor go as.runActor(actor) fmt.Printf("Actor %s: Restarted\n", actor.ref.id) } else { // Stop the actor and notify supervisor fmt.Printf("Actor %s: Max restarts exceeded, stopping\n", actor.ref.id) if actor.supervisor != nil { actor.supervisor.Send(ActorFailedMessage{ FailedActor: actor.ref, Error: err, }) } } } // Stop stops the actor system func (as *ActorSystem) Stop() { as.cancel() // Wait a bit for actors to stop gracefully time.Sleep(100 * time.Millisecond) fmt.Println("ActorSystem: Stopped") } // Message types for actor system type ActorFailedMessage struct { FailedActor *ActorRef Error error } type CreateChildMessage struct { ChildID string Behavior ActorBehavior ResponseChan chan *ActorRef } type WorkMessage struct { Data string } type ResultMessage struct { Result string From *ActorRef } // WorkerActor demonstrates a worker that can fail func WorkerBehavior(ctx ActorContext, message Message) { switch msg := message.(type) { case WorkMessage: fmt.Printf("Worker %s: Processing work: %s\n", ctx.Self.id, msg.Data) // Simulate work time.Sleep(100 * time.Millisecond) // Simulate random failures if len(msg.Data)%7 == 0 { panic("simulated worker failure") } result := fmt.Sprintf("processed-%s", msg.Data) fmt.Printf("Worker %s: Work completed: %s\n", ctx.Self.id, result) default: fmt.Printf("Worker %s: Unknown message: %T\n", ctx.Self.id, message) } } // SupervisorActor manages worker actors func SupervisorBehavior(ctx ActorContext, message Message) { switch msg := message.(type) { case CreateChildMessage: childRef := ctx.System.ActorOf(msg.ChildID, msg.Behavior, ctx.Self) msg.ResponseChan <- childRef case ActorFailedMessage: fmt.Printf("Supervisor %s: Child actor %s failed: %v\n", ctx.Self.id, msg.FailedActor.id, msg.Error) // Create replacement worker newWorkerID := fmt.Sprintf("%s-replacement", msg.FailedActor.id) ctx.System.ActorOf(newWorkerID, WorkerBehavior, ctx.Self) fmt.Printf("Supervisor %s: Created replacement worker %s\n", ctx.Self.id, newWorkerID) case WorkMessage: // Delegate work to children (simplified) fmt.Printf("Supervisor %s: Delegating work: %s\n", ctx.Self.id, msg.Data) default: fmt.Printf("Supervisor %s: Unknown message: %T\n", ctx.Self.id, message) } } func main() { fmt.Println("=== Advanced Actor System Demo ===") system := NewActorSystem() defer system.Stop() // Create supervisor supervisor := system.ActorOf("supervisor", SupervisorBehavior, nil) // Create workers through supervisor responseChan := make(chan *ActorRef) supervisor.Send(CreateChildMessage{ ChildID: "worker-1", Behavior: WorkerBehavior, ResponseChan: responseChan, }) worker1 := <-responseChan supervisor.Send(CreateChildMessage{ ChildID: "worker-2", Behavior: WorkerBehavior, ResponseChan: responseChan, }) worker2 := <-responseChan // Send work to workers workItems := []string{ "task-1", "task-2", "task-3", "failure", // "failure" will cause panic "task-4", "task-5", "another", "task-6", } for i, work := range workItems { var worker *ActorRef if i%2 == 0 { worker = worker1 } else { worker = worker2 } worker.Send(WorkMessage{Data: work}) time.Sleep(200 * time.Millisecond) } // Wait for processing time.Sleep(3 * time.Second) } Distributed Actor System package main import ( "context" "encoding/json" "fmt" "net" "sync" "time" ) // RemoteMessage represents a message that can be sent over network type RemoteMessage struct { Type string `json:"type"` Payload interface{} `json:"payload"` From string `json:"from"` To string `json:"to"` } // DistributedActorSystem extends ActorSystem with network capabilities type DistributedActorSystem struct { *ActorSystem nodeID string address string listener net.Listener peers map[string]net.Conn peersMu sync.RWMutex } // NewDistributedActorSystem creates a new distributed actor system func NewDistributedActorSystem(nodeID, address string) *DistributedActorSystem { return &DistributedActorSystem{ ActorSystem: NewActorSystem(), nodeID: nodeID, address: address, peers: make(map[string]net.Conn), } } // Start starts the distributed actor system func (das *DistributedActorSystem) Start() error { listener, err := net.Listen("tcp", das.address) if err != nil { return err } das.listener = listener // Accept incoming connections go func() { for { conn, err := listener.Accept() if err != nil { return } go das.handleConnection(conn) } }() fmt.Printf("DistributedActorSystem %s: Started on %s\n", das.nodeID, das.address) return nil } // ConnectToPeer connects to a peer node func (das *DistributedActorSystem) ConnectToPeer(peerID, peerAddress string) error { conn, err := net.Dial("tcp", peerAddress) if err != nil { return err } das.peersMu.Lock() das.peers[peerID] = conn das.peersMu.Unlock() go das.handleConnection(conn) fmt.Printf("DistributedActorSystem %s: Connected to peer %s\n", das.nodeID, peerID) return nil } // handleConnection handles incoming network connections func (das *DistributedActorSystem) handleConnection(conn net.Conn) { defer conn.Close() decoder := json.NewDecoder(conn) for { var msg RemoteMessage if err := decoder.Decode(&msg); err != nil { return } das.handleRemoteMessage(msg) } } // handleRemoteMessage processes remote messages func (das *DistributedActorSystem) handleRemoteMessage(msg RemoteMessage) { fmt.Printf("DistributedActorSystem %s: Received remote message from %s to %s\n", das.nodeID, msg.From, msg.To) // Find local actor and deliver message das.ActorSystem.mu.RLock() actor, exists := das.ActorSystem.actors[msg.To] das.ActorSystem.mu.RUnlock() if exists { // Convert payload back to proper message type switch msg.Type { case "work": if data, ok := msg.Payload.(string); ok { actor.ref.Send(WorkMessage{Data: data}) } case "result": if result, ok := msg.Payload.(string); ok { actor.ref.Send(ResultMessage{Result: result}) } } } } // SendRemoteMessage sends a message to a remote actor func (das *DistributedActorSystem) SendRemoteMessage(peerID, actorID string, message Message) error { das.peersMu.RLock() conn, exists := das.peers[peerID] das.peersMu.RUnlock() if !exists { return fmt.Errorf("peer %s not connected", peerID) } var msgType string var payload interface{} switch msg := message.(type) { case WorkMessage: msgType = "work" payload = msg.Data case ResultMessage: msgType = "result" payload = msg.Result default: return fmt.Errorf("unsupported message type: %T", message) } remoteMsg := RemoteMessage{ Type: msgType, Payload: payload, From: das.nodeID, To: actorID, } encoder := json.NewEncoder(conn) return encoder.Encode(remoteMsg) } // Stop stops the distributed actor system func (das *DistributedActorSystem) Stop() { if das.listener != nil { das.listener.Close() } das.peersMu.Lock() for _, conn := range das.peers { conn.Close() } das.peersMu.Unlock() das.ActorSystem.Stop() } // DistributedWorkerBehavior for distributed workers func DistributedWorkerBehavior(system *DistributedActorSystem) ActorBehavior { return func(ctx ActorContext, message Message) { switch msg := message.(type) { case WorkMessage: fmt.Printf("DistributedWorker %s: Processing work: %s\n", ctx.Self.id, msg.Data) // Simulate work time.Sleep(500 * time.Millisecond) result := fmt.Sprintf("processed-%s-by-%s", msg.Data, system.nodeID) fmt.Printf("DistributedWorker %s: Work completed: %s\n", ctx.Self.id, result) // Send result back (in real system, would send to requester) default: fmt.Printf("DistributedWorker %s: Unknown message: %T\n", ctx.Self.id, message) } } } func main() { fmt.Println("=== Distributed Actor System Demo ===") // Create two distributed actor systems system1 := NewDistributedActorSystem("node1", "localhost:8001") system2 := NewDistributedActorSystem("node2", "localhost:8002") // Start systems if err := system1.Start(); err != nil { panic(err) } defer system1.Stop() if err := system2.Start(); err != nil { panic(err) } defer system2.Stop() // Wait for systems to start time.Sleep(100 * time.Millisecond) // Connect systems if err := system1.ConnectToPeer("node2", "localhost:8002"); err != nil { panic(err) } if err := system2.ConnectToPeer("node1", "localhost:8001"); err != nil { panic(err) } // Create distributed workers worker1 := system1.ActorOf("worker1", DistributedWorkerBehavior(system1), nil) worker2 := system2.ActorOf("worker2", DistributedWorkerBehavior(system2), nil) // Send local work worker1.Send(WorkMessage{Data: "local-task-1"}) worker2.Send(WorkMessage{Data: "local-task-2"}) // Send remote work system1.SendRemoteMessage("node2", "worker2", WorkMessage{Data: "remote-task-from-node1"}) system2.SendRemoteMessage("node1", "worker1", WorkMessage{Data: "remote-task-from-node2"}) // Wait for processing time.Sleep(2 * time.Second) } Best Practices Keep Actors Small: Each actor should have a single responsibility Immutable Messages: Use immutable data structures for messages Avoid Blocking: Don’t block in actor message handlers Handle Failures: Implement proper supervision and error handling Message Ordering: Design for message reordering in distributed systems Backpressure: Handle mailbox overflow gracefully Testing: Test actors in isolation with mock messages Common Pitfalls Shared State: Accidentally sharing mutable state between actors Blocking Operations: Performing blocking I/O in message handlers Large Messages: Sending large objects instead of references Circular Dependencies: Creating circular message dependencies Resource Leaks: Not properly cleaning up actor resources Synchronous Communication: Trying to make actor communication synchronous When to Use Actor Model Use When: ...