How do you implement a worker pool in Go?

// Classic worker pool pattern
func workerPool(ctx context.Context, jobs <-chan Job, results chan<- Result, numWorkers int) {
    var wg sync.WaitGroup

    for i := 0; i < numWorkers; i++ {
        wg.Add(1)
        go func(id int) {
            defer wg.Done()
            for {
                select {
                case <-ctx.Done():
                    return // cancelled
                case job, ok := <-jobs:
                    if !ok { return } // channel closed — no more jobs
                    result := process(job)
                    select {
                    case results <- result:
                    case <-ctx.Done(): return
                    }
                }
            }
        }(i)
    }

    // Close results after all workers finish
    go func() {
        wg.Wait()
        close(results)
    }()
}

// Usage
const numWorkers = 10
jobs    := make(chan Job, 100)
results := make(chan Result, 100)

ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()

workerPool(ctx, jobs, results, numWorkers)

// Feed jobs
go func() {
    defer close(jobs)
    for _, job := range allJobs {
        select {
        case jobs <- job:
        case <-ctx.Done(): return
        }
    }
}()

// Collect results
for r := range results {
    fmt.Println(r)
}