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c5b92f71d4
* Fix storage/remote.pool interned refs count and flaky test I saw TestIntern_MultiRef_Concurrent failing on a different PR saying 'expected refs to be 1 but it was 2'. I took a look, and it definitely can be racy, especially with a time.Sleep() of just 1ms. I'm fixing that by explicitly waiting until it has been released, and by repeating that 1000 times, otherwise it's just a recipe for a future flaky test. OTOH, I also took a look at the implementation and saw that we were not holding the RLock() when increasing the references count, so when releasing there was a race condition for the cleanup, I fixed that by holding RLock() while increasing the references count. Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com> * s/Equalf/Equal/ Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com> --------- Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
107 lines
2.3 KiB
Go
107 lines
2.3 KiB
Go
// Copyright 2019 The Prometheus Authors
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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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// Inspired / copied / modified from https://gitlab.com/cznic/strutil/blob/master/strutil.go,
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// which is MIT licensed, so:
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//
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// Copyright (c) 2014 The strutil Authors. All rights reserved.
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package remote
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import (
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"sync"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/client_golang/prometheus/promauto"
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"go.uber.org/atomic"
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)
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var noReferenceReleases = promauto.NewCounter(prometheus.CounterOpts{
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Namespace: namespace,
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Subsystem: subsystem,
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Name: "string_interner_zero_reference_releases_total",
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Help: "The number of times release has been called for strings that are not interned.",
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})
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type pool struct {
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mtx sync.RWMutex
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pool map[string]*entry
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}
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type entry struct {
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refs atomic.Int64
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s string
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}
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func newEntry(s string) *entry {
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return &entry{s: s}
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}
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func newPool() *pool {
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return &pool{
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pool: map[string]*entry{},
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}
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}
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func (p *pool) intern(s string) string {
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if s == "" {
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return ""
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}
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p.mtx.RLock()
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interned, ok := p.pool[s]
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if ok {
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// Increase the reference count while we're still holding the read lock,
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// This will prevent the release() from deleting the entry while we're increasing its ref count.
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interned.refs.Inc()
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p.mtx.RUnlock()
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return interned.s
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}
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p.mtx.RUnlock()
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p.mtx.Lock()
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defer p.mtx.Unlock()
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if interned, ok := p.pool[s]; ok {
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interned.refs.Inc()
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return interned.s
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}
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p.pool[s] = newEntry(s)
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p.pool[s].refs.Store(1)
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return s
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}
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func (p *pool) release(s string) {
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p.mtx.RLock()
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interned, ok := p.pool[s]
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p.mtx.RUnlock()
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if !ok {
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noReferenceReleases.Inc()
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return
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}
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refs := interned.refs.Dec()
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if refs > 0 {
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return
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}
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p.mtx.Lock()
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defer p.mtx.Unlock()
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if interned.refs.Load() != 0 {
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return
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}
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delete(p.pool, s)
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}
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