What causes goroutine leaks and how do you prevent and detect them?

A goroutine leak occurs when a goroutine starts but never terminates — it blocks indefinitely waiting on a channel, lock, or I/O that will never complete. Leaked goroutines accumulate over time, consuming memory and potentially holding references that prevent GC, causing steady memory growth until OOM.

// LEAK 1: nobody ever sends to ch — goroutine parks forever
func leak1() {
    ch := make(chan int)
    go func() {
        v := <-ch  // blocks; function returns; nobody sends → leaked
        process(v)
    }()
}

// FIX: use context for cancellation
func fixed1(ctx context.Context) {
    ch := make(chan int)
    go func() {
        select {
        case v := <-ch:   process(v)
        case <-ctx.Done(): return
        }
    }()
}

// LEAK 2: jobs channel never closed
func leak2() {
    jobs := make(chan Job)
    go func() {
        for job := range jobs { process(job) } // waits forever
    }()
    // forgot close(jobs) → goroutine never exits
}

// LEAK 3: time.Ticker never stopped
func leak3() {
    ticker := time.NewTicker(time.Second)
    go func() {
        for range ticker.C { doWork() } // runs forever
    }()
    // forgot ticker.Stop() → goroutine and channel leaked
}

// DETECTION:
// runtime.NumGoroutine()         — watch for steady growth
// /debug/pprof/goroutine?debug=2 — full goroutine stack traces
// goleak library in tests:
// import "go.uber.org/goleak"
// defer goleak.VerifyNone(t)  // fails test if goroutines leak

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