Web Go 多线程编程示例

// Web Go Goroutines Examples
// Creating and managing goroutines for concurrent execution

package main

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

// 1. Basic Goroutine

// simpleGoroutine demonstrates a basic goroutine
func simpleGoroutine(id int) {
	fmt.Printf("Goroutine %d is running\n", id)
}

// BasicGoroutineExample shows how to create a basic goroutine
func BasicGoroutineExample() {
	fmt.Println("--- Basic Goroutine ---")

	// Launch multiple goroutines
	for i := 1; i <= 3; i++ {
		go simpleGoroutine(i)
	}

	// Wait for goroutines to finish
	time.Sleep(time.Second)
	fmt.Println("Main function completed")
}

// 2. Goroutine with WaitGroup

// workerWithWaitGroup demonstrates using WaitGroup
func workerWithWaitGroup(id int, wg *sync.WaitGroup) {
	defer wg.Done()
	fmt.Printf("Worker %d starting\n", id)

	// Simulate work
	time.Sleep(500 * time.Millisecond)

	fmt.Printf("Worker %d completed\n", id)
}

// WaitGroupExample demonstrates using WaitGroup to wait for goroutines
func WaitGroupExample() {
	fmt.Println("\n--- Goroutine with WaitGroup ---")

	var wg sync.WaitGroup

	// Launch 3 workers
	for i := 1; i <= 3; i++ {
		wg.Add(1)
		go workerWithWaitGroup(i, &wg)
	}

	// Wait for all workers to complete
	wg.Wait()
	fmt.Println("All workers completed")
}

// 3. Goroutine with Parameters

// processTask processes a task with parameters
func processTask(taskID int, taskName string, duration time.Duration) {
	fmt.Printf("Task %d (%s) started\n", taskID, taskName)
	time.Sleep(duration)
	fmt.Printf("Task %d (%s) completed in %v\n", taskID, taskName, duration)
}

// GoroutineWithParametersExample shows passing parameters to goroutines
func GoroutineWithParametersExample() {
	fmt.Println("\n--- Goroutine with Parameters ---")

	// Launch goroutines with different parameters
	go processTask(1, "Download", 300*time.Millisecond)
	go processTask(2, "Process", 500*time.Millisecond)
	go processTask(3, "Upload", 200*time.Millisecond)

	// Wait for completion
	time.Sleep(time.Second)
}

// 4. Anonymous Goroutine

// AnonymousGoroutineExample demonstrates anonymous goroutines
func AnonymousGoroutineExample() {
	fmt.Println("\n--- Anonymous Goroutine ---")

	for i := 1; i <= 3; i++ {
		go func(id int) {
			fmt.Printf("Anonymous goroutine %d\n", id)
		}(i)
	}

	time.Sleep(500 * time.Millisecond)
}

// 5. Goroutine with Return Values (using channels)

// computeResult performs computation and returns result via channel
func computeResult(a, b int, resultChan chan<- int) {
	result := a + b
	resultChan <- result
}

// GoroutineWithReturnValueExample shows getting return values from goroutines
func GoroutineWithReturnValueExample() {
	fmt.Println("\n--- Goroutine with Return Values ---")

	resultChan := make(chan int)

	go computeResult(10, 20, resultChan)

	// Wait for result
	result := <-resultChan
	fmt.Printf("Result from goroutine: %d\n", result)
}

// 6. Multiple Goroutines with Multiple Return Values

// divideAndRemainder calculates division and remainder
func divideAndRemainder(a, b int, resultChan chan<- [2]int) {
	quotient := a / b
	remainder := a % b
	resultChan <- [2]int{quotient, remainder}
}

// MultipleReturnValuesExample demonstrates multiple return values
func MultipleReturnValuesExample() {
	fmt.Println("\n--- Multiple Return Values ---")

	resultChan := make(chan [2]int)

	go divideAndRemainder(17, 5, resultChan)

	result := <-resultChan
	fmt.Printf("Quotient: %d, Remainder: %d\n", result[0], result[1])
}

// 7. Controlling Number of Goroutines

// LimitedGoroutinesExample shows how to limit concurrent goroutines
func LimitedGoroutinesExample() {
	fmt.Println("\n--- Limited Concurrent Goroutines ---")

	maxConcurrent := 2
	semaphore := make(chan struct{}, maxConcurrent)
	var wg sync.WaitGroup

	tasks := []string{"Task1", "Task2", "Task3", "Task4", "Task5"}

	for _, task := range tasks {
		wg.Add(1)

		// Acquire semaphore
		semaphore <- struct{}{}

		go func(taskName string) {
			defer wg.Done()
			defer func() { <-semaphore }() // Release semaphore

			fmt.Printf("%s started\n", taskName)
			time.Sleep(300 * time.Millisecond)
			fmt.Printf("%s completed\n", taskName)
		}(task)
	}

	wg.Wait()
	fmt.Println("All tasks completed")
}

// 8. Goroutine Lifecycle Management

// ManagedGoroutine manages goroutine lifecycle
func ManagedGoroutine(id int, stopChan <-chan struct{}) {
	fmt.Printf("Goroutine %d started\n", id)

	ticker := time.NewTicker(100 * time.Millisecond)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			fmt.Printf("Goroutine %d working\n", id)
		case <-stopChan:
			fmt.Printf("Goroutine %d stopping\n", id)
			return
		}
	}
}

// GoroutineLifecycleExample demonstrates managing goroutine lifecycle
func GoroutineLifecycleExample() {
	fmt.Println("\n--- Goroutine Lifecycle Management ---")

	stopChan := make(chan struct{})

	// Start managed goroutine
	go ManagedGoroutine(1, stopChan)

	// Let it run for 500ms
	time.Sleep(500 * time.Millisecond)

	// Stop the goroutine
	close(stopChan)
	time.Sleep(100 * time.Millisecond)

	fmt.Println("Goroutine stopped")
}

// 9. Goroutine Panic Recovery

// safeGoroutine demonstrates panic recovery in goroutines
func safeGoroutine(id int, wg *sync.WaitGroup) {
	defer wg.Done()
	defer func() {
		if r := recover(); r != nil {
			fmt.Printf("Goroutine %d recovered from panic: %v\n", id, r)
		}
	}()

	if id == 2 {
		panic("Intentional panic in goroutine 2")
	}

	fmt.Printf("Goroutine %d completed successfully\n", id)
}

// PanicRecoveryExample shows how to handle panics in goroutines
func PanicRecoveryExample() {
	fmt.Println("\n--- Panic Recovery in Goroutines ---")

	var wg sync.WaitGroup

	for i := 1; i <= 3; i++ {
		wg.Add(1)
		go safeGoroutine(i, &wg)
	}

	wg.Wait()
	fmt.Println("All goroutines completed (with recovery)")
}

// 10. Goroutine Statistics

// GoroutineStatsExample shows goroutine statistics
func GoroutineStatsExample() {
	fmt.Println("\n--- Goroutine Statistics ---")

	// Get initial number of goroutines
	startingCount := runtime.NumGoroutine()
	fmt.Printf("Initial goroutine count: %d\n", startingCount)

	// Launch some goroutines
	var wg sync.WaitGroup
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			time.Sleep(100 * time.Millisecond)
		}(i)
	}

	runningCount := runtime.NumGoroutine()
	fmt.Printf("Running goroutine count: %d\n", runningCount)

	wg.Wait()

	finalCount := runtime.NumGoroutine()
	fmt.Printf("Final goroutine count: %d\n", finalCount)
}

// 11. Goroutine with Timeout

// workerWithTimeout demonstrates goroutine with timeout
func workerWithTimeout(id int, timeout time.Duration, done chan<- bool) {
	select {
	case <-time.After(timeout):
		fmt.Printf("Worker %d completed within timeout\n", id)
		done <- true
	case <-time.After(2 * timeout):
		fmt.Printf("Worker %d timed out\n", id)
		done <- false
	}
}

// TimeoutExample demonstrates timeout handling with goroutines
func TimeoutExample() {
	fmt.Println("\n--- Goroutine with Timeout ---")

	doneChan := make(chan bool)

	go workerWithTimeout(1, 300*time.Millisecond, doneChan)

	result := <-doneChan
	if result {
		fmt.Println("Worker completed successfully")
	} else {
		fmt.Println("Worker timed out")
	}
}

// 12. Fan-out Pattern

// processWithFanOut demonstrates fan-out pattern
func processWithFanOut(tasks []string, results chan<- string) {
	for _, task := range tasks {
		go func(t string) {
			time.Sleep(100 * time.Millisecond)
			results <- fmt.Sprintf("Processed: %s", t)
		}(task)
	}
}

// FanOutExample demonstrates fan-out pattern
func FanOutExample() {
	fmt.Println("\n--- Fan-out Pattern ---")

	tasks := []string{"Task1", "Task2", "Task3", "Task4", "Task5"}
	results := make(chan string, len(tasks))

	processWithFanOut(tasks, results)

	// Collect results
	for i := 0; i < len(tasks); i++ {
		result := <-results
		fmt.Println(result)
	}

	fmt.Println("All tasks processed")
}

// Main function demonstrating all examples
func main() {
	fmt.Println("=== Web Go Goroutines Examples ===\n")

	BasicGoroutineExample()
	WaitGroupExample()
	GoroutineWithParametersExample()
	AnonymousGoroutineExample()
	GoroutineWithReturnValueExample()
	MultipleReturnValuesExample()
	LimitedGoroutinesExample()
	GoroutineLifecycleExample()
	PanicRecoveryExample()
	GoroutineStatsExample()
	TimeoutExample()
	FanOutExample()

	fmt.Println("\n=== All Goroutine Examples Completed ===")
}

// Web Go Thread Synchronization Examples
// Synchronizing goroutines using mutexes, channels, and other sync primitives

package main

import (
	"fmt"
	"sync"
	"sync/atomic"
	"time"
)

// 1. Mutex (Mutual Exclusion)

// SafeCounter demonstrates using mutex to protect shared data
type SafeCounter struct {
	mu    sync.Mutex
	value int
}

// Increment increments the counter safely
func (c *SafeCounter) Increment() {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.value++
}

// Value returns the current value
func (c *SafeCounter) Value() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.value
}

// MutexExample demonstrates basic mutex usage
func MutexExample() {
	fmt.Println("--- Mutex Example ---")

	counter := SafeCounter{}
	var wg sync.WaitGroup

	// Launch 100 goroutines to increment counter
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			counter.Increment()
		}()
	}

	wg.Wait()
	fmt.Printf("Final counter value: %d\n", counter.Value())
}

// 2. RWMutex (Read-Write Mutex)

// ThreadSafeMap demonstrates using RWMutex for multiple readers
type ThreadSafeMap struct {
	mu    sync.RWMutex
	data  map[string]int
}

// NewThreadSafeMap creates a new thread-safe map
func NewThreadSafeMap() *ThreadSafeMap {
	return &ThreadSafeMap{
		data: make(map[string]int),
	}
}

// Get reads a value (allows multiple concurrent readers)
func (m *ThreadSafeMap) Get(key string) (int, bool) {
	m.mu.RLock()
	defer m.mu.RUnlock()
	val, ok := m.data[key]
	return val, ok
}

// Set writes a value (exclusive lock)
func (m *ThreadSafeMap) Set(key string, value int) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.data[key] = value
}

// RWMutexExample demonstrates read-write mutex
func RWMutexExample() {
	fmt.Println("\n--- RWMutex Example ---")

	tsMap := NewThreadSafeMap()
	var wg sync.WaitGroup

	// Writers
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			key := fmt.Sprintf("key%d", id)
			tsMap.Set(key, id*10)
			fmt.Printf("Writer: Set %s = %d\n", key, id*10)
		}(i)
	}

	// Readers
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			key := fmt.Sprintf("key%d", id%5)
			if val, ok := tsMap.Get(key); ok {
				fmt.Printf("Reader: Got %s = %d\n", key, val)
			}
		}(i)
	}

	wg.Wait()
	fmt.Println("All readers and writers completed")
}

// 3. Once (Single Execution)

// Singleton demonstrates using sync.Once
type Singleton struct {
	data string
}

var (
	instance *Singleton
	once     sync.Once
)

// GetInstance returns the singleton instance
func GetInstance() *Singleton {
	once.Do(func() {
		instance = &Singleton{data: "Singleton initialized"}
		fmt.Println("Singleton created")
	})
	return instance
}

// OnceExample demonstrates sync.Once usage
func OnceExample() {
	fmt.Println("\n--- Once Example ---")

	var wg sync.WaitGroup

	// Multiple goroutines trying to get singleton
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			inst := GetInstance()
			fmt.Printf("Goroutine %d got instance: %p\n", id, inst)
		}(i)
	}

	wg.Wait()
}

// 4. WaitGroup

// WaitGroupExample demonstrates WaitGroup for waiting on multiple goroutines
func WaitGroupExample() {
	fmt.Println("\n--- WaitGroup Example ---")

	var wg sync.WaitGroup
	tasks := []string{"Download", "Process", "Upload", "Verify"}

	for _, task := range tasks {
		wg.Add(1)
		go func(taskName string) {
			defer wg.Done()
			fmt.Printf("%s started\n", taskName)
			time.Sleep(200 * time.Millisecond)
			fmt.Printf("%s completed\n", taskName)
		}(task)
	}

	wg.Wait()
	fmt.Println("All tasks completed")
}

// 5. Channels for Synchronization

// ChannelSyncExample demonstrates using channels for synchronization
func ChannelSyncExample() {
	fmt.Println("\n--- Channel Synchronization Example ---")

	done := make(chan bool)

	// Worker goroutine
	go func() {
		fmt.Println("Worker started")
		time.Sleep(500 * time.Millisecond)
		fmt.Println("Worker completed")
		done <- true
	}()

	fmt.Println("Main waiting for worker...")
	<-done
	fmt.Println("Main received completion signal")
}

// 6. Buffered Channels

// BufferedChannelExample demonstrates buffered channels
func BufferedChannelExample() {
	fmt.Println("\n--- Buffered Channel Example ---")

	// Create buffered channel with capacity 3
	ch := make(chan string, 3)

	// Producer
	go func() {
		for i := 1; i <= 5; i++ {
			msg := fmt.Sprintf("Message %d", i)
			ch <- msg
			fmt.Printf("Sent: %s\n", msg)
		}
		close(ch)
	}()

	// Consumer
	time.Sleep(100 * time.Millisecond) // Let producer send some messages
	for msg := range ch {
		fmt.Printf("Received: %s\n", msg)
		time.Sleep(100 * time.Millisecond)
	}
}

// 7. Select Statement

// SelectExample demonstrates select for multiple channel operations
func SelectExample() {
	fmt.Println("\n--- Select Statement Example ---")

	ch1 := make(chan string)
	ch2 := make(chan string)

	go func() {
		time.Sleep(100 * time.Millisecond)
		ch1 <- "Channel 1 message"
	}()

	go func() {
		time.Sleep(200 * time.Millisecond)
		ch2 <- "Channel 2 message"
	}()

	// Receive from whichever channel is ready first
	for i := 0; i < 2; i++ {
		select {
		case msg := <-ch1:
			fmt.Printf("Received from ch1: %s\n", msg)
		case msg := <-ch2:
			fmt.Printf("Received from ch2: %s\n", msg)
		}
	}
}

// 8. Select with Timeout

// SelectTimeoutExample demonstrates timeout with select
func SelectTimeoutExample() {
	fmt.Println("\n--- Select with Timeout Example ---")

	ch := make(chan string)

	go func() {
		time.Sleep(500 * time.Millisecond)
		ch <- "Delayed message"
	}()

	select {
	case msg := <-ch:
		fmt.Printf("Received: %s\n", msg)
	case <-time.After(200 * time.Millisecond):
		fmt.Println("Timeout occurred")
	}
}

// 9. Atomic Operations

// AtomicExample demonstrates atomic operations
func AtomicExample() {
	fmt.Println("\n--- Atomic Operations Example ---")

	var counter int64
	var wg sync.WaitGroup

	for i := 0; i < 1000; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			atomic.AddInt64(&counter, 1)
		}()
	}

	wg.Wait()
	fmt.Printf("Final counter value (atomic): %d\n", atomic.LoadInt64(&counter))
}

// 10. Condition Variables

// CondExample demonstrates condition variables
func CondExample() {
	fmt.Println("\n--- Condition Variable Example ---")

	var mu sync.Mutex
	cond := sync.NewCond(&mu)
	ready := false

	// Worker goroutine
	go func() {
		mu.Lock()
		for !ready {
			cond.Wait()
		}
		fmt.Println("Worker: Condition met, proceeding...")
		mu.Unlock()
	}()

	// Main goroutine
	time.Sleep(100 * time.Millisecond)
	mu.Lock()
	ready = true
	fmt.Println("Main: Signaling condition")
	cond.Signal()
	mu.Unlock()

	time.Sleep(100 * time.Millisecond)
}

var cond *sync.Cond

// 11. ErrGroup (Error Group)

// ErrGroupExample demonstrates error handling with goroutines
func ErrGroupExample() {
	fmt.Println("\n--- ErrGroup Example ---")

	g, ctx := sync.ErrGroup(ctx.Background())

	// Launch multiple goroutines
	for i := 1; i <= 3; i++ {
		id := i
		g.Go(func() error {
			time.Sleep(time.Duration(id) * 100 * time.Millisecond)
			if id == 2 {
				return fmt.Errorf("error in goroutine %d", id)
			}
			fmt.Printf("Goroutine %d completed\n", id)
			return nil
		})
	}

	if err := g.Wait(); err != nil {
		fmt.Printf("ErrGroup finished with error: %v\n", err)
	}
}

// 12. Worker Pool Pattern

// WorkerPoolExample demonstrates worker pool pattern
func WorkerPoolExample() {
	fmt.Println("\n--- Worker Pool Example ---")

	jobs := make(chan int, 100)
	results := make(chan int, 100)

	// Start 3 workers
	for w := 1; w <= 3; w++ {
		go worker(w, jobs, results)
	}

	// Send 5 jobs
	for j := 1; j <= 5; j++ {
		jobs <- j
		fmt.Printf("Sent job %d\n", j)
	}
	close(jobs)

	// Collect results
	for j := 1; j <= 5; j++ {
		result := <-results
		fmt.Printf("Received result %d\n", result)
	}
}

func worker(id int, jobs <-chan int, results chan<- int) {
	for job := range jobs {
		fmt.Printf("Worker %d processing job %d\n", id, job)
		time.Sleep(100 * time.Millisecond)
		results <- job * 2
	}
}

// Main function
func main() {
	fmt.Println("=== Web Go Thread Synchronization Examples ===\n")

	MutexExample()
	RWMutexExample()
	OnceExample()
	WaitGroupExample()
	ChannelSyncExample()
	BufferedChannelExample()
	SelectExample()
	SelectTimeoutExample()
	AtomicExample()
	CondExample()
	ErrGroupExample()
	WorkerPoolExample()

	fmt.Println("\n=== All Thread Synchronization Examples Completed ===")
}

// Web Go Worker Pool Examples
// Implementing worker pools for efficient concurrent task processing

package main

import (
	"fmt"
	"sync"
	"time"
)

// 1. Basic Worker Pool

// Job represents a unit of work
type Job struct {
	ID   int
	Data string
}

// Result represents the result of a job
type Result struct {
	JobID  int
	Output string
	Error  error
}

// WorkerPool represents a pool of workers
type WorkerPool struct {
	workerCount int
	jobs        chan Job
	results     chan Result
	wg          sync.WaitGroup
}

// NewWorkerPool creates a new worker pool
func NewWorkerPool(workerCount int) *WorkerPool {
	return &WorkerPool{
		workerCount: workerCount,
		jobs:        make(chan Job, 100),
		results:     make(chan Result, 100),
	}
}

// Start starts the worker pool
func (wp *WorkerPool) Start() {
	for i := 0; i < wp.workerCount; i++ {
		wp.wg.Add(1)
		go wp.worker(i)
	}
}

// worker processes jobs from the job channel
func (wp *WorkerPool) worker(id int) {
	defer wp.wg.Done()

	for job := range wp.jobs {
		fmt.Printf("Worker %d processing job %d\n", id, job.ID)

		// Simulate work
		time.Sleep(100 * time.Millisecond)

		// Send result
		wp.results <- Result{
			JobID:  job.ID,
			Output: fmt.Sprintf("Job %d processed by worker %d", job.ID, id),
		}
	}
}

// Submit submits a job to the pool
func (wp *WorkerPool) Submit(job Job) {
	wp.jobs <- job
}

// Stop stops the worker pool
func (wp *WorkerPool) Stop() {
	close(wp.jobs)
	wp.wg.Wait()
	close(wp.results)
}

// Results returns a channel for reading results
func (wp *WorkerPool) Results() <-chan Result {
	return wp.results
}

// BasicWorkerPoolExample demonstrates basic worker pool
func BasicWorkerPoolExample() {
	fmt.Println("--- Basic Worker Pool Example ---")

	pool := NewWorkerPool(3)
	pool.Start()

	// Submit jobs
	for i := 1; i <= 5; i++ {
		job := Job{
			ID:   i,
			Data: fmt.Sprintf("Task %d", i),
		}
		pool.Submit(job)
	}

	// Wait for all results to be processed
	go func() {
		time.Sleep(time.Second)
		pool.Stop()
	}()

	// Collect results
	for range pool.Results() {
		// Results consumed
	}

	fmt.Println("All jobs completed")
}

// 2. Worker Pool with Error Handling

// JobWithErr represents a job that might fail
type JobWithErr struct {
	ID      int
	ShouldFail bool
}

// WorkerPoolWithError handles jobs with error tracking
type WorkerPoolWithError struct {
	workerCount int
	jobs        chan JobWithErr
	results     chan Result
	errors      chan error
	wg          sync.WaitGroup
}

// NewWorkerPoolWithError creates a new worker pool with error handling
func NewWorkerPoolWithError(workerCount int) *WorkerPoolWithError {
	return &WorkerPoolWithError{
		workerCount: workerCount,
		jobs:        make(chan JobWithErr, 100),
		results:     make(chan Result, 100),
		errors:      make(chan error, 100),
	}
}

// Start starts the worker pool
func (wp *WorkerPoolWithError) Start() {
	for i := 0; i < wp.workerCount; i++ {
		wp.wg.Add(1)
		go wp.worker(i)
	}
}

// worker processes jobs with error handling
func (wp *WorkerPoolWithError) worker(id int) {
	defer wp.wg.Done()

	for job := range wp.jobs {
		fmt.Printf("Worker %d processing job %d\n", id, job.ID)

		time.Sleep(100 * time.Millisecond)

		if job.ShouldFail {
			wp.errors <- fmt.Errorf("job %d failed", job.ID)
		} else {
			wp.results <- Result{
				JobID:  job.ID,
				Output: fmt.Sprintf("Job %d processed successfully", job.ID),
			}
		}
	}
}

// Submit submits a job to the pool
func (wp *WorkerPoolWithError) Submit(job JobWithErr) {
	wp.jobs <- job
}

// Stop stops the worker pool
func (wp *WorkerPoolWithError) Stop() {
	close(wp.jobs)
	wp.wg.Wait()
	close(wp.results)
	close(wp.errors)
}

// WorkerPoolWithErrorExample demonstrates worker pool with error handling
func WorkerPoolWithErrorExample() {
	fmt.Println("\n--- Worker Pool with Error Handling ---")

	pool := NewWorkerPoolWithError(2)
	pool.Start()

	// Submit jobs
	for i := 1; i <= 5; i++ {
		job := JobWithErr{
			ID:         i,
			ShouldFail: i%3 == 0, // Every 3rd job fails
		}
		pool.Submit(job)
	}

	// Wait for processing
	go func() {
		time.Sleep(time.Second)
		pool.Stop()
	}()

	// Collect results
	for {
		select {
		case result, ok := <-pool.results:
			if !ok {
				pool.results = nil
			} else {
				fmt.Printf("Success: %s\n", result.Output)
			}
		case err, ok := <-pool.errors:
			if !ok {
				pool.errors = nil
			} else {
				fmt.Printf("Error: %v\n", err)
			}
		}

		if pool.results == nil && pool.errors == nil {
			break
		}
	}

	fmt.Println("Worker pool stopped")
}

// 3. Dynamic Worker Pool

// DynamicWorkerPool can resize the number of workers
type DynamicWorkerPool struct {
	minWorkers  int
	maxWorkers  int
	jobs        chan Job
	results     chan Result
	workerCount int
	mu          sync.Mutex
	wg          sync.WaitGroup
	quit        chan struct{}
}

// NewDynamicWorkerPool creates a new dynamic worker pool
func NewDynamicWorkerPool(minWorkers, maxWorkers int) *DynamicWorkerPool {
	pool := &DynamicWorkerPool{
		minWorkers: minWorkers,
		maxWorkers: maxWorkers,
		jobs:       make(chan Job, 100),
		results:    make(chan Result, 100),
		quit:       make(chan struct{}),
	}

	// Start minimum workers
	for i := 0; i < minWorkers; i++ {
		pool.addWorker()
	}

	return pool
}

// addWorker adds a new worker
func (dp *DynamicWorkerPool) addWorker() {
	dp.wg.Add(1)
	dp.workerCount++

	go func() {
		defer func() {
			dp.wg.Done()
			dp.mu.Lock()
			dp.workerCount--
			dp.mu.Unlock()
		}()

		for {
			select {
			case job, ok := <-dp.jobs:
				if !ok {
					return
				}

				fmt.Printf("Worker processing job %d\n", job.ID)
				time.Sleep(100 * time.Millisecond)

				dp.results <- Result{
					JobID:  job.ID,
					Output: fmt.Sprintf("Job %d processed", job.ID),
				}
			case <-dp.quit:
				return
			}
		}
	}()
}

// ScaleUp increases the number of workers
func (dp *DynamicWorkerPool) ScaleUp(count int) {
	dp.mu.Lock()
	defer dp.mu.Unlock()

	currentWorkers := dp.workerCount
	available := dp.maxWorkers - currentWorkers

	if available <= 0 {
		fmt.Println("Already at max workers")
		return
	}

	toAdd := count
	if toAdd > available {
		toAdd = available
	}

	for i := 0; i < toAdd; i++ {
		dp.addWorker()
	}

	fmt.Printf("Scaled up from %d to %d workers\n", currentWorkers, dp.workerCount)
}

// ScaleDown decreases the number of workers
func (dp *DynamicWorkerPool) ScaleDown(count int) {
	dp.mu.Lock()
	defer dp.mu.Unlock()

	currentWorkers := dp.workerCount
	available := currentWorkers - dp.minWorkers

	if available <= 0 {
		fmt.Println("Already at min workers")
		return
	}

	toRemove := count
	if toRemove > available {
		toRemove = available
	}

	// Signal workers to quit
	for i := 0; i < toRemove; i++ {
		dp.quit <- struct{}{}
	}

	fmt.Printf("Scaled down from %d to %d workers\n", currentWorkers, currentWorkers-toRemove)
}

// Submit submits a job to the pool
func (dp *DynamicWorkerPool) Submit(job Job) {
	dp.jobs <- job
}

// Stop stops the worker pool
func (dp *DynamicWorkerPool) Stop() {
	close(dp.jobs)
	dp.wg.Wait()
	close(dp.results)
}

// GetWorkerCount returns current worker count
func (dp *DynamicWorkerPool) GetWorkerCount() int {
	dp.mu.Lock()
	defer dp.mu.Unlock()
	return dp.workerCount
}

// DynamicWorkerPoolExample demonstrates dynamic worker pool
func DynamicWorkerPoolExample() {
	fmt.Println("\n--- Dynamic Worker Pool Example ---")

	pool := NewDynamicWorkerPool(2, 5)

	fmt.Printf("Initial workers: %d\n", pool.GetWorkerCount())

	// Scale up
	pool.ScaleUp(2)
	fmt.Printf("After scale up: %d\n", pool.GetWorkerCount())

	// Submit jobs
	for i := 1; i <= 10; i++ {
		pool.Submit(Job{ID: i, Data: fmt.Sprintf("Task %d", i)})
	}

	// Collect some results
	for i := 0; i < 5; i++ {
		<-pool.results
	}

	// Scale down
	pool.ScaleDown(2)
	fmt.Printf("After scale down: %d\n", pool.GetWorkerCount())

	// Stop pool
	go func() {
		time.Sleep(500 * time.Millisecond)
		pool.Stop()
	}()

	for range pool.results {
		// Drain remaining results
	}

	fmt.Println("Dynamic worker pool stopped")
}

// 4. Worker Pool with Context

// Context-aware worker pool
type ContextWorkerPool struct {
	workerCount int
	jobs        chan Job
	results     chan Result
	cancel      chan struct{}
	wg          sync.WaitGroup
}

// NewContextWorkerPool creates a context-aware worker pool
func NewContextWorkerPool(workerCount int) *ContextWorkerPool {
	return &ContextWorkerPool{
		workerCount: workerCount,
		jobs:        make(chan Job, 100),
		results:     make(chan Result, 100),
		cancel:      make(chan struct{}),
	}
}

// Start starts the worker pool
func (cp *ContextWorkerPool) Start() {
	for i := 0; i < cp.workerCount; i++ {
		cp.wg.Add(1)
		go cp.worker(i)
	}
}

// worker processes jobs with context awareness
func (cp *ContextWorkerPool) worker(id int) {
	defer cp.wg.Done()

	for {
		select {
		case job, ok := <-cp.jobs:
			if !ok {
				return
			}

			fmt.Printf("Worker %d processing job %d\n", id, job.ID)

			// Check for cancellation
			select {
			case <-cp.cancel:
				fmt.Printf("Worker %d: job %d cancelled\n", id, job.ID)
				return
			default:
			}

			time.Sleep(100 * time.Millisecond)

			cp.results <- Result{
				JobID:  job.ID,
				Output: fmt.Sprintf("Job %d processed", job.ID),
			}
		case <-cp.cancel:
			fmt.Printf("Worker %d: received cancel signal\n", id)
			return
		}
	}
}

// Submit submits a job to the pool
func (cp *ContextWorkerPool) Submit(job Job) {
	cp.jobs <- job
}

// Cancel cancels all workers
func (cp *ContextWorkerPool) Cancel() {
	close(cp.cancel)
}

// Stop stops the worker pool
func (cp *ContextWorkerPool) Stop() {
	close(cp.jobs)
	cp.wg.Wait()
	close(cp.results)
}

// ContextWorkerPoolExample demonstrates context-aware worker pool
func ContextWorkerPoolExample() {
	fmt.Println("\n--- Context Worker Pool Example ---")

	pool := NewContextWorkerPool(3)
	pool.Start()

	// Submit jobs
	for i := 1; i <= 5; i++ {
		pool.Submit(Job{ID: i, Data: fmt.Sprintf("Task %d", i)})
	}

	// Let some work complete
	time.Sleep(200 * time.Millisecond)

	// Cancel remaining work
	fmt.Println("Cancelling worker pool...")
	pool.Cancel()

	time.Sleep(100 * time.Millisecond)
	pool.Stop()

	fmt.Println("Context worker pool cancelled and stopped")
}

// Main function
func main() {
	fmt.Println("=== Web Go Worker Pool Examples ===\n")

	BasicWorkerPoolExample()
	WorkerPoolWithErrorExample()
	DynamicWorkerPoolExample()
	ContextWorkerPoolExample()

	fmt.Println("\n=== All Worker Pool Examples Completed ===")
}