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time: clarify Timer.Reset behavior on AfterFunc Timers

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Fixes #28100

Change-Id: I37d4d7badf455e4ecf982d4fc7cb070052de2e45
Reviewed-on: https://go-review.googlesource.com/c/go/+/285632
Trust: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Brad Fitzpatrick 2021-01-21 19:41:56 -08:00
parent cf10e69f17
commit 50cba0506f
1 changed files with 12 additions and 1 deletions
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13
src/time/sleep.go
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@ -101,7 +101,9 @@ func NewTimer(d Duration) *Timer {
// It returns true if the timer had been active, false if the timer had // It returns true if the timer had been active, false if the timer had
// expired or been stopped. // 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 // 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. // 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, // 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. // 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. // Reset should always be invoked on stopped or expired channels, as described above.
// The return value exists to preserve compatibility with existing programs. // 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 { func (t *Timer) Reset(d Duration) bool {
if t.r.f == nil { if t.r.f == nil {
panic("time: Reset called on uninitialized Timer") panic("time: Reset called on uninitialized Timer")