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92 lines
2.8 KiB
92 lines
2.8 KiB
/*
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* Copyright 2019 Dgraph Labs, Inc. and Contributors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package ristretto
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import (
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"sync"
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)
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// ringConsumer is the user-defined object responsible for receiving and
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// processing items in batches when buffers are drained.
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type ringConsumer interface {
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Push([]uint64) bool
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}
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// ringStripe is a singular ring buffer that is not concurrent safe.
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type ringStripe struct {
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cons ringConsumer
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data []uint64
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capa int
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}
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func newRingStripe(cons ringConsumer, capa int64) *ringStripe {
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return &ringStripe{
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cons: cons,
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data: make([]uint64, 0, capa),
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capa: int(capa),
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}
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}
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// Push appends an item in the ring buffer and drains (copies items and
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// sends to Consumer) if full.
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func (s *ringStripe) Push(item uint64) {
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s.data = append(s.data, item)
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// Decide if the ring buffer should be drained.
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if len(s.data) >= s.capa {
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// Send elements to consumer and create a new ring stripe.
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if s.cons.Push(s.data) {
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s.data = make([]uint64, 0, s.capa)
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} else {
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s.data = s.data[:0]
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}
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}
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}
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// ringBuffer stores multiple buffers (stripes) and distributes Pushed items
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// between them to lower contention.
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//
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// This implements the "batching" process described in the BP-Wrapper paper
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// (section III part A).
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type ringBuffer struct {
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pool *sync.Pool
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}
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// newRingBuffer returns a striped ring buffer. The Consumer in ringConfig will
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// be called when individual stripes are full and need to drain their elements.
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func newRingBuffer(cons ringConsumer, capa int64) *ringBuffer {
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// LOSSY buffers use a very simple sync.Pool for concurrently reusing
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// stripes. We do lose some stripes due to GC (unheld items in sync.Pool
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// are cleared), but the performance gains generally outweigh the small
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// percentage of elements lost. The performance primarily comes from
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// low-level runtime functions used in the standard library that aren't
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// available to us (such as runtime_procPin()).
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return &ringBuffer{
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pool: &sync.Pool{
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New: func() interface{} { return newRingStripe(cons, capa) },
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},
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}
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}
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// Push adds an element to one of the internal stripes and possibly drains if
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// the stripe becomes full.
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func (b *ringBuffer) Push(item uint64) {
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// Reuse or create a new stripe.
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stripe := b.pool.Get().(*ringStripe)
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stripe.Push(item)
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b.pool.Put(stripe)
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}
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