How do you implement a worker pool in Go?

A worker pool limits the number of goroutines working concurrently, preventing resource exhaustion when processing a large number of tasks. It is one of the most common Go concurrency patterns.

// 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)
}

The worker pool pattern ensures bounded concurrency — with virtual threads in other languages this is less critical, but in Go it matters when each goroutine holds OS resources (database connections, file handles) that are finite. Set numWorkers based on the resource constraint: for I/O-bound work constrained by a connection pool of size N, use N workers. For CPU-bound work, use runtime.NumCPU() workers.

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