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bounded_queue.go
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bounded_queue.go
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// Copyright (c) 2017 Uber Technologies, Inc.
//
// 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 queue
import (
"sync"
"sync/atomic"
"time"
"github.com/uber/jaeger-lib/metrics"
)
// BoundedQueue implements a producer-consumer exchange similar to a ring buffer queue,
// where the queue is bounded and if it fills up due to slow consumers, the new items written by
// the producer force the earliest items to be dropped. The implementation is actually based on
// channels, with a special Reaper goroutine that wakes up when the queue is full and consumers
// the items from the top of the queue until its size drops back to maxSize
type BoundedQueue struct {
capacity int
size int32
onDroppedItem func(item interface{})
items chan interface{}
stopCh chan struct{}
stopWG sync.WaitGroup
stopped int32
}
// NewBoundedQueue constructs the new queue of specified capacity, and with an optional
// callback for dropped items (e.g. useful to emit metrics).
func NewBoundedQueue(capacity int, onDroppedItem func(item interface{})) *BoundedQueue {
return &BoundedQueue{
capacity: capacity,
onDroppedItem: onDroppedItem,
items: make(chan interface{}, capacity),
stopCh: make(chan struct{}),
}
}
// StartConsumers starts a given number of goroutines consuming items from the queue
// and passing them into the consumer callback.
func (q *BoundedQueue) StartConsumers(num int, consumer func(item interface{})) {
var startWG sync.WaitGroup
for i := 0; i < num; i++ {
q.stopWG.Add(1)
startWG.Add(1)
go func() {
startWG.Done()
defer q.stopWG.Done()
for {
select {
case item := <-q.items:
atomic.AddInt32(&q.size, -1)
consumer(item)
case <-q.stopCh:
return
}
}
}()
}
startWG.Wait()
}
// Produce is used by the producer to submit new item to the queue. Returns false in case of queue overflow.
func (q *BoundedQueue) Produce(item interface{}) bool {
if atomic.LoadInt32(&q.stopped) != 0 {
q.onDroppedItem(item)
return false
}
select {
case q.items <- item:
atomic.AddInt32(&q.size, 1)
return true
default:
if q.onDroppedItem != nil {
q.onDroppedItem(item)
}
return false
}
}
// Stop stops all consumers, as well as the length reporter if started,
// and releases the items channel. It blocks until all consumers have stopped.
func (q *BoundedQueue) Stop() {
atomic.StoreInt32(&q.stopped, 1) // disable producer
close(q.stopCh)
q.stopWG.Wait()
close(q.items)
}
// Size returns the current size of the queue
func (q *BoundedQueue) Size() int {
return int(atomic.LoadInt32(&q.size))
}
// Capacity returns capacity of the queue
func (q *BoundedQueue) Capacity() int {
return q.capacity
}
// StartLengthReporting starts a timer-based gorouting that periodically reports
// current queue length to a given metrics gauge.
func (q *BoundedQueue) StartLengthReporting(reportPeriod time.Duration, gauge metrics.Gauge) {
ticker := time.NewTicker(reportPeriod)
go func() {
defer ticker.Stop()
for {
select {
case <-ticker.C:
size := q.Size()
gauge.Update(int64(size))
case <-q.stopCh:
return
}
}
}()
}