flowcontrol context aware and fix request may hang issue

Kubernetes-commit: ce8805f95fcf6540397eaa60b8d84db752f05eea

util/flowcontrol/throttle.go

@@ -17,6 +17,8 @@ limitations under the License.
 package flowcontrol
 
 import (
+	"context"
+	"errors"
 	"sync"
 	"time"
 
@@ -33,6 +35,8 @@ type RateLimiter interface {
 	Stop()
 	// QPS returns QPS of this rate limiter
 	QPS() float32
+	// Wait returns nil if a token is taken before the Context is done.
+	Wait(ctx context.Context) error
 }
 
 type tokenBucketRateLimiter struct {
@@ -98,6 +102,10 @@ func (t *tokenBucketRateLimiter) QPS() float32 {
 	return t.qps
 }
 
+func (t *tokenBucketRateLimiter) Wait(ctx context.Context) error {
+	return t.limiter.Wait(ctx)
+}
+
 type fakeAlwaysRateLimiter struct{}
 
 func NewFakeAlwaysRateLimiter() RateLimiter {
@@ -116,6 +124,10 @@ func (t *fakeAlwaysRateLimiter) QPS() float32 {
 	return 1
 }
 
+func (t *fakeAlwaysRateLimiter) Wait(ctx context.Context) error {
+	return nil
+}
+
 type fakeNeverRateLimiter struct {
 	wg sync.WaitGroup
 }
@@ -141,3 +153,7 @@ func (t *fakeNeverRateLimiter) Accept() {
 func (t *fakeNeverRateLimiter) QPS() float32 {
 	return 1
 }
+
+func (t *fakeNeverRateLimiter) Wait(ctx context.Context) error {
+	return errors.New("can not be accept")
+}