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bucket.go
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bucket.go
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// Copyright 2015 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 trafficshape
import (
"errors"
"sync"
"sync/atomic"
"time"
"github.com/google/martian/log"
)
// Bucket is a generic leaky bucket that drains at a configurable interval and
// fills at user defined rate. The bucket may be used concurrently.
type Bucket struct {
capacity int64 // atomic
fill int64 // atomic
mu sync.Mutex
t *time.Ticker
closec chan struct{}
}
var (
// ErrBucketOverflow is an error that indicates the bucket has been overflown
// by the user. This error is only returned iff fill > capacity.
ErrBucketOverflow = errors.New("trafficshape: bucket overflow")
errFillClosedBucket = errors.New("trafficshape: fill on closed bucket")
)
// NewBucket returns a new leaky bucket with capacity that is drained
// at interval.
func NewBucket(capacity int64, interval time.Duration) *Bucket {
b := &Bucket{
capacity: capacity,
t: time.NewTicker(interval),
closec: make(chan struct{}),
}
go b.loop()
return b
}
// Capacity returns the capacity of the bucket.
func (b *Bucket) Capacity() int64 {
return atomic.LoadInt64(&b.capacity)
}
// SetCapacity sets the capacity for the bucket and resets the fill to zero.
func (b *Bucket) SetCapacity(capacity int64) {
log.Infof("trafficshape: set capacity: %d", capacity)
atomic.StoreInt64(&b.capacity, capacity)
atomic.StoreInt64(&b.fill, 0)
}
// Close stops the drain loop and marks the bucket as closed.
func (b *Bucket) Close() error {
log.Debugf("trafficshape: closing bucket")
// Allow b to be closed multiple times without panicking.
if b.closed() {
return nil
}
b.t.Stop()
close(b.closec)
return nil
}
// FillThrottle calls fn with the available capacity remaining (capacity-fill)
// and fills the bucket with the number of tokens returned by fn. If the
// remaining capacity is <= 0, FillThrottle will wait for the next drain before
// running fn.
//
// If fn returns an error, it will be returned by FillThrottle along with the
// number of tokens processed by fn.
//
// fn is provided the remaining capacity as a soft maximum, fn is allowed to
// use more than the remaining capacity without incurring spillage.
//
// If the bucket is closed when FillThrottle is called, or while waiting for
// the next drain, fn will not be executed and FillThrottle will return with an
// error.
func (b *Bucket) FillThrottle(fn func(int64) (int64, error)) (int64, error) {
for {
if b.closed() {
log.Errorf("trafficshape: fill on closed bucket")
return 0, errFillClosedBucket
}
fill := atomic.LoadInt64(&b.fill)
capacity := atomic.LoadInt64(&b.capacity)
if fill < capacity {
log.Debugf("trafficshape: under capacity (%d/%d)", fill, capacity)
n, err := fn(capacity - fill)
fill = atomic.AddInt64(&b.fill, n)
return n, err
}
log.Debugf("trafficshape: bucket full (%d/%d)", fill, capacity)
}
}
// FillThrottleLocked is like FillThrottle, except that it uses a lock to protect
// the critical section between accessing the fill value and updating it.
func (b *Bucket) FillThrottleLocked(fn func(int64) (int64, error)) (int64, error) {
for {
if b.closed() {
log.Errorf("trafficshape: fill on closed bucket")
return 0, errFillClosedBucket
}
b.mu.Lock()
fill := atomic.LoadInt64(&b.fill)
capacity := atomic.LoadInt64(&b.capacity)
if fill < capacity {
n, err := fn(capacity - fill)
fill = atomic.AddInt64(&b.fill, n)
b.mu.Unlock()
return n, err
}
b.mu.Unlock()
log.Debugf("trafficshape: bucket full (%d/%d)", fill, capacity)
}
}
// Fill calls fn with the available capacity remaining (capacity-fill) and
// fills the bucket with the number of tokens returned by fn. If the remaining
// capacity is 0, Fill returns 0, nil. If the remaining capacity is < 0, Fill
// returns 0, ErrBucketOverflow.
//
// If fn returns an error, it will be returned by Fill along with the remaining
// capacity.
//
// fn is provided the remaining capacity as a soft maximum, fn is allowed to
// use more than the remaining capacity without incurring spillage, though this
// will cause subsequent calls to Fill to return ErrBucketOverflow until the
// next drain.
//
// If the bucket is closed when Fill is called, fn will not be executed and
// Fill will return with an error.
func (b *Bucket) Fill(fn func(int64) (int64, error)) (int64, error) {
if b.closed() {
log.Errorf("trafficshape: fill on closed bucket")
return 0, errFillClosedBucket
}
fill := atomic.LoadInt64(&b.fill)
capacity := atomic.LoadInt64(&b.capacity)
switch {
case fill < capacity:
log.Debugf("trafficshape: under capacity (%d/%d)", fill, capacity)
n, err := fn(capacity - fill)
fill = atomic.AddInt64(&b.fill, n)
return n, err
case fill > capacity:
log.Debugf("trafficshape: bucket overflow (%d/%d)", fill, capacity)
return 0, ErrBucketOverflow
}
log.Debugf("trafficshape: bucket full (%d/%d)", fill, capacity)
return 0, nil
}
// loop drains the fill at interval and returns when the bucket is closed.
func (b *Bucket) loop() {
log.Debugf("trafficshape: started drain loop")
defer log.Debugf("trafficshape: stopped drain loop")
for {
select {
case t := <-b.t.C:
atomic.StoreInt64(&b.fill, 0)
log.Debugf("trafficshape: fill reset @ %s", t)
case <-b.closec:
log.Debugf("trafficshape: bucket closed")
return
}
}
}
func (b *Bucket) closed() bool {
select {
case <-b.closec:
return true
default:
return false
}
}