Example for https://github.com/cockroachdb/cockroach/issues/89716#issuecomment-1274079219

leaking_timer.go

package main

import (
	"fmt"
	"math/rand"
	"runtime"
	"sync"
	"time"
)

func tickerLoop(wg *sync.WaitGroup, quit chan struct{}) {
	t := time.NewTicker(time.Duration(10+rand.Intn(20)) * time.Millisecond)
	defer wg.Done()
	// NB: uncomment to fix a memory leak
	defer t.Stop()

	select {
	case <-t.C:
	case <-quit:
		return
	}
}

func createTickers(n int, quit chan struct{}) {
	wg := new(sync.WaitGroup)
	wg.Add(n)
	fmt.Printf("Making %d tickers\n", n)

	for i := 0; i < n; i++ {
		go tickerLoop(wg, quit)
	}
	// NB: quit will exit out of the goroutine, effectively allowing to GC ticker's channel.
	//     However, the global 'timers' array continues to point to ticker's 'runtimeTimer' struct
        //     unless `Stop` is called.
	close(quit)
	
	wg.Wait()
}

func main() {
	const n = 100000
	quit := make(chan struct{})

	var start, end runtime.MemStats
	runtime.GC()
	runtime.ReadMemStats(&start)

	createTickers(n, quit)

	// Run a dummy goroutine so that select {} doesn't throw a tantrum.
        // It panics otherwise -- fatal error: all goroutines are asleep - deadlock!
	i := 0
	go func() {
		for {
			i += 1
			time.Sleep(1 * time.Millisecond)
		}
	}()
	time.Sleep(2 * time.Second)

	runtime.GC()
	runtime.ReadMemStats(&end)
	alloc := end.TotalAlloc - start.TotalAlloc
	fmt.Printf("Total heap: %d\n", alloc)

	fmt.Printf("Sleeping... check CPU utilization\n")

	select {}
}