runtime: avoid an allocation in (*time.Timer).Reset

Author: eliasnaur

src/runtime/scheduler.go

@@ -39,20 +39,17 @@ func timerQueueAdd(tn *timerNode) {
 	*q = tn
 }
 
-func timerQueueRemove(t *timer) bool {
-	removedTimer := false
+func timerQueueRemove(t *timer) *timerNode {
 	for q := &timerQueue; *q != nil; q = &(*q).next {
 		if (*q).timer == t {
 			scheduleLog("removed timer")
+			n := *q
 			*q = (*q).next
-			removedTimer = true
-			break
+			return n
 		}
 	}
-	if !removedTimer {
-		scheduleLog("did not remove timer")
-	}
-	return removedTimer
+	scheduleLog("did not remove timer")
+	return nil
 }
 
 // Goexit terminates the currently running goroutine. No other goroutines are affected.

src/runtime/scheduler_cooperative.go

@@ -117,11 +117,11 @@ func addTimer(tim *timerNode) {
 
 // removeTimer is the implementation of time.stopTimer. It removes a timer from
 // the timer queue, returning true if the timer is present in the timer queue.
-func removeTimer(tim *timer) bool {
+func removeTimer(tim *timer) *timerNode {
 	mask := interrupt.Disable()
-	removedTimer := timerQueueRemove(tim)
+	n := timerQueueRemove(tim)
 	interrupt.Restore(mask)
-	return removedTimer
+	return n
 }
 
 func schedulerRunQueue() *task.Queue {

src/runtime/scheduler_none.go

@@ -56,9 +56,9 @@ func addTimer(tim *timerNode) {
 	runtimePanic("timers not supported without a scheduler")
 }
 
-func removeTimer(tim *timer) bool {
+func removeTimer(tim *timer) *timerNode {
 	runtimePanic("timers not supported without a scheduler")
-	return false
+	return nil
 }
 
 func schedulerRunQueue() *task.Queue {

src/runtime/scheduler_threads.go

@@ -110,11 +110,11 @@ func addTimer(tim *timerNode) {
 	timerQueueLock.Unlock()
 }
 
-func removeTimer(tim *timer) bool {
+func removeTimer(tim *timer) *timerNode {
 	timerQueueLock.Lock()
-	removed := timerQueueRemove(tim)
+	n := timerQueueRemove(tim)
 	timerQueueLock.Unlock()
-	return removed
+	return n
 }
 
 func schedulerRunQueue() *task.Queue {

src/runtime/time_go122.go

@@ -53,13 +53,13 @@ func startTimer(tim *timer) {
 
 //go:linkname stopTimer time.stopTimer
 func stopTimer(tim *timer) bool {
-	return removeTimer(tim)
+	return removeTimer(tim) != nil
 }
 
 //go:linkname resetTimer time.resetTimer
 func resetTimer(tim *timer, when int64) bool {
 	tim.when = when
-	removed := removeTimer(tim)
+	n := removeTimer(tim)
 	startTimer(tim)
-	return removed
+	return n != nil
 }

src/runtime/time_go123.go

@@ -52,17 +52,20 @@ func newTimer(when, period int64, f func(arg any, seq uintptr, delta int64), arg
 
 //go:linkname stopTimer time.stopTimer
 func stopTimer(tim *timeTimer) bool {
-	return removeTimer(&tim.timer)
+	return removeTimer(&tim.timer) != nil
 }
 
 //go:linkname resetTimer time.resetTimer
 func resetTimer(t *timeTimer, when, period int64) bool {
 	t.timer.when = when
 	t.timer.period = period
-	removed := removeTimer(&t.timer)
-	addTimer(&timerNode{
-		timer:    &t.timer,
-		callback: timerCallback,
-	})
+	n := removeTimer(&t.timer)
+	removed := n != nil
+	if n == nil {
+		n = new(timerNode)
+	}
+	n.timer = &t.timer
+	n.callback = timerCallback
+	addTimer(n)
 	return removed
 }