time, runtime: only call resetTimer from (*Timer).Reset

Previously we stopped the timer and then reset it. With the current
timer implementation that is no longer required.

Change-Id: Ie7aba61ad53ce835f6fcd0b6bce7fe0a15b10e24
Reviewed-on: https://go-review.googlesource.com/c/go/+/227180
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

2 files changed, 16 insertions, 9 deletions

diff --git a/src/runtime/time.go b/src/runtime/time.go
index 208fbf64c7..fdb5066b24 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -216,11 +216,12 @@ func stopTimer(t *timer) bool {
 
 // resetTimer resets an inactive timer, adding it to the heap.
 //go:linkname resetTimer time.resetTimer
-func resetTimer(t *timer, when int64) {
+// Reports whether the timer was modified before it was run.
+func resetTimer(t *timer, when int64) bool {
 	if raceenabled {
 		racerelease(unsafe.Pointer(t))
 	}
-	resettimer(t, when)
+	return resettimer(t, when)
 }
 
 // modTimer modifies an existing timer.
@@ -403,13 +404,15 @@ func dodeltimer0(pp *p) {
 
 // modtimer modifies an existing timer.
 // This is called by the netpoll code or time.Ticker.Reset.
-func modtimer(t *timer, when, period int64, f func(interface{}, uintptr), arg interface{}, seq uintptr) {
+// Reports whether the timer was modified before it was run.
+func modtimer(t *timer, when, period int64, f func(interface{}, uintptr), arg interface{}, seq uintptr) bool {
 	if when < 0 {
 		when = maxWhen
 	}
 
 	status := uint32(timerNoStatus)
 	wasRemoved := false
+	var pending bool
 	var mp *m
 loop:
 	for {
@@ -419,6 +422,7 @@ loop:
 			// This could lead to a self-deadlock. See #38070.
 			mp = acquirem()
 			if atomic.Cas(&t.status, status, timerModifying) {
+				pending = true // timer not yet run
 				break loop
 			}
 			releasem(mp)
@@ -431,6 +435,7 @@ loop:
 			// Act like addtimer.
 			if atomic.Cas(&t.status, status, timerModifying) {
 				wasRemoved = true
+				pending = false // timer already run or stopped
 				break loop
 			}
 			releasem(mp)
@@ -440,6 +445,7 @@ loop:
 			mp = acquirem()
 			if atomic.Cas(&t.status, status, timerModifying) {
 				atomic.Xadd(&t.pp.ptr().deletedTimers, -1)
+				pending = false // timer already stopped
 				break loop
 			}
 			releasem(mp)
@@ -510,14 +516,17 @@ loop:
 			wakeNetPoller(when)
 		}
 	}
+
+	return pending
 }
 
 // resettimer resets the time when a timer should fire.
 // If used for an inactive timer, the timer will become active.
 // This should be called instead of addtimer if the timer value has been,
 // or may have been, used previously.
-func resettimer(t *timer, when int64) {
-	modtimer(t, when, t.period, t.f, t.arg, t.seq)
+// Reports whether the timer was modified before it was run.
+func resettimer(t *timer, when int64) bool {
+	return modtimer(t, when, t.period, t.f, t.arg, t.seq)
 }
 
 // cleantimers cleans up the head of the timer queue. This speeds up
diff --git a/src/time/sleep.go b/src/time/sleep.go
index bd0ed9aaba..22ffd68282 100644
--- a/src/time/sleep.go
+++ b/src/time/sleep.go
@@ -38,7 +38,7 @@ func when(d Duration) int64 {
 
 func startTimer(*runtimeTimer)
 func stopTimer(*runtimeTimer) bool
-func resetTimer(*runtimeTimer, int64)
+func resetTimer(*runtimeTimer, int64) bool
 func modTimer(t *runtimeTimer, when, period int64, f func(interface{}, uintptr), arg interface{}, seq uintptr)
 
 // The Timer type represents a single event.
@@ -123,9 +123,7 @@ func (t *Timer) Reset(d Duration) bool {
 		panic("time: Reset called on uninitialized Timer")
 	}
 	w := when(d)
-	active := stopTimer(&t.r)
-	resetTimer(&t.r, w)
-	return active
+	return resetTimer(&t.r, w)
 }
 
 func sendTime(c interface{}, seq uintptr) {