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Golang / GoLang Concurrency Mastery Interview Questions

What are the differences between time.After, time.NewTimer, and time.NewTicker, and which leaks resources?

All three involve time-based channel operations but have distinct behaviours, reuse capabilities, and resource management responsibilities.

Time Facility Comparison
APIReturnsFiresResource leak riskReusable
time.After(d)<-chan TimeOnce, after dGoroutine + channel until d expires if case not takenNo
time.NewTimer(d)*time.TimerOnce, after dMust call Stop()Yes (via Reset)
time.NewTicker(d)*time.TickerEvery d foreverMUST call Stop() — goroutine lives until Stop or process exitYes (until stopped)
// time.After — convenient but leaks if the receive case is not taken
select {
case result := <-doWork():
    fmt.Println(result)
case <-time.After(5 * time.Second):
    fmt.Println("timeout")
    // If doWork wins: timer goroutine and channel live for 5s — avoid in loops
}

// time.NewTimer — correct approach for loops or where early stop is needed
timer := time.NewTimer(5 * time.Second)
defer timer.Stop()  // always stop
select {
case result := <-doWork():
    timer.Stop()
    fmt.Println(result)
case <-timer.C:
    fmt.Println("timeout")
}

// time.NewTicker — periodic work, must stop
ticker := time.NewTicker(1 * time.Second)
defer ticker.Stop()  // MUST stop — goroutine lives until Stop() called
for {
    select {
    case <-ticker.C:  doPeriodicWork()
    case <-ctx.Done(): return
    }
}

// Production: context.WithTimeout is preferred for request deadlines
ctx, cancel := context.WithTimeout(parentCtx, 5*time.Second)
defer cancel()

Why should time.After be avoided inside a tight loop?
What must you do with a time.NewTicker when it is no longer needed?

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