Implement fan-out and fan-in concurrency patterns in Go.

Fan-out: distribute work from one source to multiple worker goroutines. Fan-in: merge results from multiple goroutines back into a single channel. Together they form Go's fundamental parallel pipeline pattern.

// Fan-out: distribute jobs to N workers
func fanOut(ctx context.Context, jobs <-chan Job, workers int) []<-chan Result {
    outputs := make([]<-chan Result, workers)
    for i := 0; i < workers; i++ {
        out := make(chan Result)
        outputs[i] = out
        go func(o chan<- Result) {
            defer close(o)
            for {
                select {
                case <-ctx.Done(): return
                case job, ok := <-jobs:
                    if !ok { return }
                    o <- process(job)
                }
            }
        }(out)
    }
    return outputs
}

// Fan-in: merge N result channels into one
func fanIn(ctx context.Context, channels ...<-chan Result) <-chan Result {
    var wg sync.WaitGroup
    merged := make(chan Result)

    forward := func(c <-chan Result) {
        defer wg.Done()
        for r := range c {
            select {
            case merged <- r:
            case <-ctx.Done(): return
            }
        }
    }

    wg.Add(len(channels))
    for _, c := range channels { go forward(c) }

    go func() { wg.Wait(); close(merged) }()
    return merged
}

// Wire it together
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
jobs := make(chan Job, 100)
go generateJobs(jobs)
results := fanIn(ctx, fanOut(ctx, jobs, 8)...)
for r := range results { fmt.Println(r) }

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