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/*
* Copyright 2019 Dgraph Labs, Inc. and Contributors
*
* 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 ristretto
import (
"sync"
)
// ringConsumer is the user-defined object responsible for receiving and
// processing items in batches when buffers are drained.
type ringConsumer interface {
Push([]uint64) bool
}
// ringStripe is a singular ring buffer that is not concurrent safe.
type ringStripe struct {
cons ringConsumer
data []uint64
capa int
}
func newRingStripe(cons ringConsumer, capa int64) *ringStripe {
return &ringStripe{
cons: cons,
data: make([]uint64, 0, capa),
capa: int(capa),
}
}
// Push appends an item in the ring buffer and drains (copies items and
// sends to Consumer) if full.
func (s *ringStripe) Push(item uint64) {
s.data = append(s.data, item)
// if we should drain
if len(s.data) >= s.capa {
// Send elements to consumer. Create a new one.
if s.cons.Push(s.data) {
s.data = make([]uint64, 0, s.capa)
} else {
s.data = s.data[:0]
}
}
}
// ringBuffer stores multiple buffers (stripes) and distributes Pushed items
// between them to lower contention.
//
// This implements the "batching" process described in the BP-Wrapper paper
// (section III part A).
type ringBuffer struct {
stripes []*ringStripe
pool *sync.Pool
}
// newRingBuffer returns a striped ring buffer. The Consumer in ringConfig will
// be called when individual stripes are full and need to drain their elements.
func newRingBuffer(cons ringConsumer, capa int64) *ringBuffer {
// LOSSY buffers use a very simple sync.Pool for concurrently reusing
// stripes. We do lose some stripes due to GC (unheld items in sync.Pool
// are cleared), but the performance gains generally outweigh the small
// percentage of elements lost. The performance primarily comes from
// low-level runtime functions used in the standard library that aren't
// available to us (such as runtime_procPin()).
return &ringBuffer{
pool: &sync.Pool{
New: func() interface{} { return newRingStripe(cons, capa) },
},
}
}
// Push adds an element to one of the internal stripes and possibly drains if
// the stripe becomes full.
func (b *ringBuffer) Push(item uint64) {
// reuse or create a new stripe
stripe := b.pool.Get().(*ringStripe)
stripe.Push(item)
b.pool.Put(stripe)
}
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