lease: rate limit revoke runLoop

Fix etcd-io#8097.

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

lease/lessor.go

@@ -15,6 +15,7 @@
 package lease
 
 import (
+	"context"
 	"encoding/binary"
 	"errors"
 	"math"
@@ -26,11 +27,17 @@ import (
 	"github.com/coreos/etcd/lease/leasepb"
 	"github.com/coreos/etcd/mvcc/backend"
 	"github.com/coreos/etcd/pkg/monotime"
+
+	"golang.org/x/time/rate"
 )
 
 const (
 	// NoLease is a special LeaseID representing the absence of a lease.
 	NoLease = LeaseID(0)
+
+	// maximum number of leases to revoke per second
+	// TODO: make this configurable?
+	leaseRevokesPerSecond = 1000
 )
 
 var (
@@ -412,7 +419,8 @@ func (le *lessor) Stop() {
 func (le *lessor) runLoop() {
 	defer close(le.doneC)
 
-	for {
+	revokerLimiter := rate.NewLimiter(rate.Limit(leaseRevokesPerSecond), leaseRevokesPerSecond)
+	for revokerLimiter.Wait(context.Background()) == nil {
 		var ls []*Lease
 
 		le.mu.Lock()