Other routines use atomics, hence even if we are under a lock, we should too. We might atomically store with Not sure how it happens, but it's between lines GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3974
297 lines
6.1 KiB
Go
297 lines
6.1 KiB
Go
// Copyright (C) 2015 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at http://mozilla.org/MPL/2.0/.
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package sync
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import (
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"fmt"
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"path/filepath"
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"runtime"
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"strconv"
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"strings"
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"sync"
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"sync/atomic"
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"time"
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"github.com/sasha-s/go-deadlock"
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)
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type Mutex interface {
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Lock()
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Unlock()
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}
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type RWMutex interface {
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Mutex
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RLock()
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RUnlock()
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}
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type WaitGroup interface {
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Add(int)
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Done()
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Wait()
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}
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func NewMutex() Mutex {
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if useDeadlock {
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return &deadlock.Mutex{}
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}
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if debug {
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mutex := &loggedMutex{}
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mutex.holder.Store(holder{})
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return mutex
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}
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return &sync.Mutex{}
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}
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func NewRWMutex() RWMutex {
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if useDeadlock {
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return &deadlock.RWMutex{}
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}
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if debug {
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mutex := &loggedRWMutex{
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readHolders: make(map[int][]holder),
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unlockers: make(chan holder, 1024),
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}
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mutex.holder.Store(holder{})
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return mutex
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}
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return &sync.RWMutex{}
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}
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func NewWaitGroup() WaitGroup {
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if debug {
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return &loggedWaitGroup{}
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}
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return &sync.WaitGroup{}
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}
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type holder struct {
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at string
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time time.Time
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goid int
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}
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func (h holder) String() string {
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if h.at == "" {
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return "not held"
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}
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return fmt.Sprintf("at %s goid: %d for %s", h.at, h.goid, time.Since(h.time))
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}
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type loggedMutex struct {
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sync.Mutex
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holder atomic.Value
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}
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func (m *loggedMutex) Lock() {
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m.Mutex.Lock()
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m.holder.Store(getHolder())
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}
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func (m *loggedMutex) Unlock() {
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currentHolder := m.holder.Load().(holder)
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duration := time.Since(currentHolder.time)
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if duration >= threshold {
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l.Debugf("Mutex held for %v. Locked at %s unlocked at %s", duration, currentHolder.at, getHolder().at)
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}
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m.holder.Store(holder{})
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m.Mutex.Unlock()
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}
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func (m *loggedMutex) Holders() string {
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return m.holder.Load().(holder).String()
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}
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type loggedRWMutex struct {
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sync.RWMutex
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holder atomic.Value
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readHolders map[int][]holder
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readHoldersMut sync.Mutex
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logUnlockers int32
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unlockers chan holder
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}
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func (m *loggedRWMutex) Lock() {
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start := time.Now()
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atomic.StoreInt32(&m.logUnlockers, 1)
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m.RWMutex.Lock()
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atomic.StoreInt32(&m.logUnlockers, 0)
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holder := getHolder()
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m.holder.Store(holder)
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duration := holder.time.Sub(start)
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if duration > threshold {
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var unlockerStrings []string
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loop:
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for {
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select {
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case holder := <-m.unlockers:
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unlockerStrings = append(unlockerStrings, holder.String())
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default:
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break loop
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}
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}
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l.Debugf("RWMutex took %v to lock. Locked at %s. RUnlockers while locking:\n%s", duration, holder.at, strings.Join(unlockerStrings, "\n"))
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}
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}
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func (m *loggedRWMutex) Unlock() {
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currentHolder := m.holder.Load().(holder)
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duration := time.Since(currentHolder.time)
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if duration >= threshold {
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l.Debugf("RWMutex held for %v. Locked at %s unlocked at %s", duration, currentHolder.at, getHolder().at)
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}
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m.holder.Store(holder{})
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m.RWMutex.Unlock()
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}
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func (m *loggedRWMutex) RLock() {
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m.RWMutex.RLock()
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holder := getHolder()
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m.readHoldersMut.Lock()
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m.readHolders[holder.goid] = append(m.readHolders[holder.goid], holder)
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m.readHoldersMut.Unlock()
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}
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func (m *loggedRWMutex) RUnlock() {
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id := goid()
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m.readHoldersMut.Lock()
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current := m.readHolders[id]
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if len(current) > 0 {
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m.readHolders[id] = current[:len(current)-1]
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}
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m.readHoldersMut.Unlock()
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if atomic.LoadInt32(&m.logUnlockers) == 1 {
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holder := getHolder()
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select {
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case m.unlockers <- holder:
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default:
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l.Debugf("Dropped holder %s as channel full", holder)
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}
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}
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m.RWMutex.RUnlock()
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}
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func (m *loggedRWMutex) Holders() string {
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output := m.holder.Load().(holder).String() + " (writer)"
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m.readHoldersMut.Lock()
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for _, holders := range m.readHolders {
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for _, holder := range holders {
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output += "\n" + holder.String() + " (reader)"
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}
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}
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m.readHoldersMut.Unlock()
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return output
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}
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type loggedWaitGroup struct {
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sync.WaitGroup
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}
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func (wg *loggedWaitGroup) Wait() {
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start := time.Now()
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wg.WaitGroup.Wait()
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duration := time.Since(start)
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if duration >= threshold {
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l.Debugf("WaitGroup took %v at %s", duration, getHolder())
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}
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}
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func getHolder() holder {
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_, file, line, _ := runtime.Caller(2)
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file = filepath.Join(filepath.Base(filepath.Dir(file)), filepath.Base(file))
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return holder{
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at: fmt.Sprintf("%s:%d", file, line),
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goid: goid(),
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time: time.Now(),
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}
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}
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func goid() int {
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var buf [64]byte
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n := runtime.Stack(buf[:], false)
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idField := strings.Fields(strings.TrimPrefix(string(buf[:n]), "goroutine "))[0]
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id, err := strconv.Atoi(idField)
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if err != nil {
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return -1
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}
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return id
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}
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// TimeoutCond is a variant on Cond. It has roughly the same semantics regarding 'L' - it must be held
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// both when broadcasting and when calling TimeoutCondWaiter.Wait()
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// Call Broadcast() to broadcast to all waiters on the TimeoutCond. Call SetupWait to create a
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// TimeoutCondWaiter configured with the given timeout, which can then be used to listen for
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// broadcasts.
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type TimeoutCond struct {
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L sync.Locker
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ch chan struct{}
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}
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// TimeoutCondWaiter is a type allowing a consumer to wait on a TimeoutCond with a timeout. Wait() may be called multiple times,
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// and will return true every time that the TimeoutCond is broadcast to. Once the configured timeout
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// expires, Wait() will return false.
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// Call Stop() to release resources once this TimeoutCondWaiter is no longer needed.
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type TimeoutCondWaiter struct {
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c *TimeoutCond
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timer *time.Timer
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}
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func NewTimeoutCond(l sync.Locker) *TimeoutCond {
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return &TimeoutCond{
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L: l,
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}
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}
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func (c *TimeoutCond) Broadcast() {
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// ch.L must be locked when calling this function
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if c.ch != nil {
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close(c.ch)
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c.ch = nil
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}
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}
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func (c *TimeoutCond) SetupWait(timeout time.Duration) *TimeoutCondWaiter {
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timer := time.NewTimer(timeout)
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return &TimeoutCondWaiter{
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c: c,
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timer: timer,
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}
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}
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func (w *TimeoutCondWaiter) Wait() bool {
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// ch.L must be locked when calling this function
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// Ensure that the channel exists, since we're going to be waiting on it
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if w.c.ch == nil {
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w.c.ch = make(chan struct{})
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}
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ch := w.c.ch
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w.c.L.Unlock()
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defer w.c.L.Lock()
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select {
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case <-w.timer.C:
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return false
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case <-ch:
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return true
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}
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}
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func (w *TimeoutCondWaiter) Stop() {
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w.timer.Stop()
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}
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