When should you use channels versus mutexes in Go concurrency?

Go's concurrency mantra is "Do not communicate by sharing memory; instead, share memory by communicating." Channels are the primary tool for passing ownership of data between goroutines; mutexes are for protecting shared state that multiple goroutines need to access concurrently.

// ── Channel: ownership transfer ──
func producer(out chan<- int) {
    for i := 0; i < 10; i++ {
        out <- i // transfer ownership of i to consumer
    }
    close(out)
}
func consumer(in <-chan int) {
    for v := range in {
        fmt.Println(v)
    }
}

// ── Mutex: protecting shared state ──
type Inventory struct {
    mu    sync.Mutex
    items map[string]int
}
func (inv *Inventory) Add(name string, qty int) {
    inv.mu.Lock()
    defer inv.mu.Unlock()
    inv.items[name] += qty
}

// ── Avoiding channel misuse ──
// Bad: using a channel as a simple mutex replacement
sem := make(chan struct{}, 1) // semaphore
sem <- struct{}{} // acquire
// critical section
<-sem             // release
// Better: just use sync.Mutex for this pattern

// Context for cancellation (not raw channels)
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
select {
case result := <-doWork(ctx):
    fmt.Println(result)
case <-ctx.Done():
    fmt.Println("timeout:", ctx.Err())
}

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