Go goroutine leak when using unbuffered channels with context cancellation

Problem

Goroutines are leaking because they block on sending to an unbuffered channel after the receiver has stopped listening (context cancelled).

Symptoms

• Memory usage grows over time
• runtime.NumGoroutine() keeps increasing
• pprof shows goroutines stuck on channel send

Stack

Solution

Always provide a way for goroutines to exit when the context is cancelled. Use select with ctx.Done() alongside channel operations. Consider using buffered channels or errgroup.

Code

// BAD: goroutine leaks if nobody reads from ch
func process(ctx context.Context) <-chan Result {
    ch := make(chan Result)
    go func() {
        result := doWork()
        ch <- result // blocks forever if ctx cancelled
    }()
    return ch
}

// GOOD: select on ctx.Done()
func process(ctx context.Context) <-chan Result {
    ch := make(chan Result, 1) // buffered so goroutine can exit
    go func() {
        result := doWork()
        select {
        case ch <- result:
        case <-ctx.Done():
        }
    }()
    return ch
}

Caveats

Even with this pattern, doWork() itself should respect context cancellation for best results.