106 lines
2.9 KiB
Go
106 lines
2.9 KiB
Go
// Copyright 2017 Google Inc. All Rights Reserved.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package pubsub
|
|
|
|
import (
|
|
"golang.org/x/net/context"
|
|
"golang.org/x/sync/semaphore"
|
|
)
|
|
|
|
// flowController implements flow control for Subscription.Receive.
|
|
type flowController struct {
|
|
maxSize int // max total size of messages
|
|
semCount, semSize *semaphore.Weighted // enforces max number and size of messages
|
|
}
|
|
|
|
// newFlowController creates a new flowController that ensures no more than
|
|
// maxCount messages or maxSize bytes are outstanding at once. If maxCount or
|
|
// maxSize is < 1, then an unlimited number of messages or bytes is permitted,
|
|
// respectively.
|
|
func newFlowController(maxCount, maxSize int) *flowController {
|
|
fc := &flowController{
|
|
maxSize: maxSize,
|
|
semCount: nil,
|
|
semSize: nil,
|
|
}
|
|
if maxCount > 0 {
|
|
fc.semCount = semaphore.NewWeighted(int64(maxCount))
|
|
}
|
|
if maxSize > 0 {
|
|
fc.semSize = semaphore.NewWeighted(int64(maxSize))
|
|
}
|
|
return fc
|
|
}
|
|
|
|
// acquire blocks until one message of size bytes can proceed or ctx is done.
|
|
// It returns nil in the first case, or ctx.Err() in the second.
|
|
//
|
|
// acquire allows large messages to proceed by treating a size greater than maxSize
|
|
// as if it were equal to maxSize.
|
|
func (f *flowController) acquire(ctx context.Context, size int) error {
|
|
if f.semCount != nil {
|
|
if err := f.semCount.Acquire(ctx, 1); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
if f.semSize != nil {
|
|
if err := f.semSize.Acquire(ctx, f.bound(size)); err != nil {
|
|
if f.semCount != nil {
|
|
f.semCount.Release(1)
|
|
}
|
|
return err
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// tryAcquire returns false if acquire would block. Otherwise, it behaves like
|
|
// acquire and returns true.
|
|
//
|
|
// tryAcquire allows large messages to proceed by treating a size greater than
|
|
// maxSize as if it were equal to maxSize.
|
|
func (f *flowController) tryAcquire(size int) bool {
|
|
if f.semCount != nil {
|
|
if !f.semCount.TryAcquire(1) {
|
|
return false
|
|
}
|
|
}
|
|
if f.semSize != nil {
|
|
if !f.semSize.TryAcquire(f.bound(size)) {
|
|
if f.semCount != nil {
|
|
f.semCount.Release(1)
|
|
}
|
|
return false
|
|
}
|
|
}
|
|
return true
|
|
}
|
|
|
|
// release notes that one message of size bytes is no longer outstanding.
|
|
func (f *flowController) release(size int) {
|
|
if f.semCount != nil {
|
|
f.semCount.Release(1)
|
|
}
|
|
if f.semSize != nil {
|
|
f.semSize.Release(f.bound(size))
|
|
}
|
|
}
|
|
|
|
func (f *flowController) bound(size int) int64 {
|
|
if size > f.maxSize {
|
|
return int64(f.maxSize)
|
|
}
|
|
return int64(size)
|
|
}
|