From 50cba0506f0f979cf1a1670ffff9113a4cdb6273 Mon Sep 17 00:00:00 2001 From: Brad Fitzpatrick Date: Thu, 21 Jan 2021 19:41:56 -0800 Subject: [PATCH] time: clarify Timer.Reset behavior on AfterFunc Timers Fixes #28100 Change-Id: I37d4d7badf455e4ecf982d4fc7cb070052de2e45 Reviewed-on: https://go-review.googlesource.com/c/go/+/285632 Trust: Brad Fitzpatrick Reviewed-by: Ian Lance Taylor --- src/time/sleep.go | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/src/time/sleep.go b/src/time/sleep.go index 90d8a18a68..4f45799414 100644 --- a/src/time/sleep.go +++ b/src/time/sleep.go @@ -101,7 +101,9 @@ func NewTimer(d Duration) *Timer { // It returns true if the timer had been active, false if the timer had // expired or been stopped. // -// Reset should be invoked only on stopped or expired timers with drained channels. +// For a Timer created with NewTimer, Reset should be invoked only on +// stopped or expired timers with drained channels. +// // If a program has already received a value from t.C, the timer is known // to have expired and the channel drained, so t.Reset can be used directly. // If a program has not yet received a value from t.C, however, @@ -120,6 +122,15 @@ func NewTimer(d Duration) *Timer { // is a race condition between draining the channel and the new timer expiring. // Reset should always be invoked on stopped or expired channels, as described above. // The return value exists to preserve compatibility with existing programs. +// +// For a Timer created with AfterFunc(d, f), Reset either reschedules +// when f will run, in which case Reset returns true, or schedules f +// to run again, in which case it returns false. +// When Reset returns false, Reset neither waits for the prior f to +// complete before returning nor does it guarantee that the subsequent +// goroutine running f does not run concurrently with the prior +// one. If the caller needs to know whether the prior execution of +// f is completed, it must coordinate with f explicitly. func (t *Timer) Reset(d Duration) bool { if t.r.f == nil { panic("time: Reset called on uninitialized Timer")