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

A goroutine leak occurs when a goroutine is started but never terminates — it blocks forever waiting on a channel, lock, or I/O operation that will never complete. Leaked goroutines consume memory (their stacks) and may hold references that prevent other objects from being GC'd. In a long-running server, goroutine leaks cause steady memory growth until OOM.

// Common leak pattern 1: unbuffered channel with no receiver
func leak1() {
    ch := make(chan int)
    go func() {
        ch <- 42 // blocks forever — nobody reads
    }()
    // function returns; the goroutine is stuck sending forever
}

// Fix: use a buffered channel, or ensure the receiver runs
func fixed1() {
    ch := make(chan int, 1) // buffered: sender doesn't block
    go func() { ch <- 42 }()
    // or: read from ch here before returning
}

// Common leak pattern 2: no cancellation signal
func leak2(ctx context.Context, jobs <-chan Job) {
    go func() {
        for {
            job := <-jobs // blocks if jobs is never closed or ctx cancelled
            process(job)
        }
    }()
}

// Fix: use select with ctx.Done()
func fixed2(ctx context.Context, jobs <-chan Job) {
    go func() {
        for {
            select {
            case <-ctx.Done(): return // clean exit on cancellation
            case job := <-jobs: process(job)
            }
        }
    }()
}

// Detecting leaks
// 1. runtime.NumGoroutine() — spot trend in tests or monitoring
// 2. http://localhost:6060/debug/pprof/goroutine?debug=2 — full traces
// 3. goleak library (uber-go/goleak) — assert no goroutines leak in tests
// import goleak "go.uber.org/goleak"
// func TestMyFunc(t *testing.T) {
//     defer goleak.VerifyNone(t)
//     myFunc()
// }

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