racy use of timers

panic.go

package main

import (
	"time"
)

func main() {
	done := make(chan struct{})

	for i := 0; i < 1000; i++ {
		tm := time.NewTimer(1 * time.Millisecond)
		go func() {
			for {
				tm.Reset(1 * time.Millisecond)
				time.Sleep(1 * time.Millisecond)
			}
		}()

		go func() {
			for {
				<-tm.C
				tm.Reset(1 * time.Millisecond) // <- If we comment this line, no panic will happen.
			}
		}()
	}

	<-done
}

stop_n_check.go

package main

import (
	"time"
)

func main() {
	done := make(chan struct{})

	for i := 0; i < 10000; i++ {
		tm := time.NewTimer(1 * time.Millisecond)
		for j := 0; j < 2; j++ {
			go func() {
				for {
					if !tm.Stop() {
						select {
						case <-tm.C:
						default:
							continue
						}
					}
					tm.Reset(1 * time.Millisecond)
					time.Sleep(1 * time.Millisecond)
				}
			}()
		}

		go func() {
			for {
				<-tm.C
				tm.Reset(1 * time.Millisecond)
			}
		}()
	}

	<-done
}