Add StoppedTimer helper (#3280)

Co-authored-by: Stephen Buttolph <stephen@avalabs.org>

network/throttling/inbound_conn_upgrade_throttler.go

@@ -11,6 +11,8 @@ import (
 	"github.com/ava-labs/avalanchego/utils/logging"
 	"github.com/ava-labs/avalanchego/utils/set"
 	"github.com/ava-labs/avalanchego/utils/timer/mockable"
+
+	timerpkg "github.com/ava-labs/avalanchego/utils/timer"
 )
 
 var (
@@ -131,10 +133,7 @@ func (n *inboundConnUpgradeThrottler) ShouldUpgrade(addrPort netip.AddrPort) boo
 }
 
 func (n *inboundConnUpgradeThrottler) Dispatch() {
-	timer := time.NewTimer(0)
-	if !timer.Stop() {
-		<-timer.C
-	}
+	timer := timerpkg.StoppedTimer()
 
 	defer timer.Stop()
 	for {

network/throttling/inbound_resource_throttler.go

@@ -15,6 +15,8 @@ import (
 	"github.com/ava-labs/avalanchego/ids"
 	"github.com/ava-labs/avalanchego/snow/networking/tracker"
 	"github.com/ava-labs/avalanchego/utils/timer/mockable"
+
+	timerpkg "github.com/ava-labs/avalanchego/utils/timer"
 )
 
 const epsilon = time.Millisecond
@@ -107,11 +109,7 @@ func NewSystemThrottler(
 		timerPool: sync.Pool{
 			New: func() interface{} {
 				// Satisfy invariant that timer is stopped and drained.
-				timer := time.NewTimer(0)
-				if !timer.Stop() {
-					<-timer.C
-				}
-				return timer
+				return timerpkg.StoppedTimer()
 			},
 		},
 	}, nil

tests/antithesis/avalanchego/main.go

@@ -33,6 +33,7 @@ import (
 	"github.com/ava-labs/avalanchego/wallet/subnet/primary"
 	"github.com/ava-labs/avalanchego/wallet/subnet/primary/common"
 
+	timerpkg "github.com/ava-labs/avalanchego/utils/timer"
 	xtxs "github.com/ava-labs/avalanchego/vms/avm/txs"
 	ptxs "github.com/ava-labs/avalanchego/vms/platformvm/txs"
 	xbuilder "github.com/ava-labs/avalanchego/wallet/chain/x/builder"
@@ -145,10 +146,7 @@ type workload struct {
 }
 
 func (w *workload) run(ctx context.Context) {
-	timer := time.NewTimer(0)
-	if !timer.Stop() {
-		<-timer.C
-	}
+	timer := timerpkg.StoppedTimer()
 
 	tc := tests.NewTestContext()
 	defer tc.Cleanup()

tests/antithesis/xsvm/main.go

@@ -26,6 +26,8 @@ import (
 	"github.com/ava-labs/avalanchego/vms/example/xsvm/api"
 	"github.com/ava-labs/avalanchego/vms/example/xsvm/cmd/issue/status"
 	"github.com/ava-labs/avalanchego/vms/example/xsvm/cmd/issue/transfer"
+
+	timerpkg "github.com/ava-labs/avalanchego/utils/timer"
 )
 
 const (
@@ -123,10 +125,7 @@ type workload struct {
 }
 
 func (w *workload) run(ctx context.Context) {
-	timer := time.NewTimer(0)
-	if !timer.Stop() {
-		<-timer.C
-	}
+	timer := timerpkg.StoppedTimer()
 
 	tc := tests.NewTestContext()
 	defer tc.Cleanup()

utils/timer/stopped_timer.go

@@ -0,0 +1,24 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package timer
+
+import "time"
+
+// StoppedTimer returns a stopped timer so that there is no entry on
+// the C channel (and there isn't one scheduled to be added).
+//
+// This means that after calling Reset there will be no events on the
+// channel until the timer fires (at which point there will be exactly
+// one event sent to the channel).
+//
+// It enables re-using the timer across loop iterations without
+// needing to have the first loop iteration perform any == nil checks
+// to initialize the first invocation.
+func StoppedTimer() *time.Timer {
+	timer := time.NewTimer(0)
+	if !timer.Stop() {
+		<-timer.C
+	}
+	return timer
+}