syncthing/lib/watchaggregator/aggregator.go

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// Copyright (C) 2016 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package watchaggregator
import (
"context"
"fmt"
"path/filepath"
"strings"
"time"
"github.com/syncthing/syncthing/lib/config"
"github.com/syncthing/syncthing/lib/events"
"github.com/syncthing/syncthing/lib/fs"
)
// Not meant to be changed, but must be changeable for tests
var (
maxFiles = 512
maxFilesPerDir = 128
)
// aggregatedEvent represents potentially multiple events at and/or recursively
// below one path until it times out and a scan is scheduled.
// If it represents multiple events and there are events of both Remove and
// NonRemove types, the evType attribute is Mixed (as returned by fs.Event.Merge).
type aggregatedEvent struct {
firstModTime time.Time
lastModTime time.Time
evType fs.EventType
}
// Stores pointers to both aggregated events directly within this directory and
// child directories recursively containing aggregated events themselves.
type eventDir struct {
events map[string]*aggregatedEvent
dirs map[string]*eventDir
}
func newEventDir() *eventDir {
return &eventDir{
events: make(map[string]*aggregatedEvent),
dirs: make(map[string]*eventDir),
}
}
func (dir *eventDir) childCount() int {
return len(dir.events) + len(dir.dirs)
}
func (dir *eventDir) firstModTime() time.Time {
if dir.childCount() == 0 {
panic("bug: firstModTime must not be used on empty eventDir")
}
firstModTime := time.Now()
for _, childDir := range dir.dirs {
dirTime := childDir.firstModTime()
if dirTime.Before(firstModTime) {
firstModTime = dirTime
}
}
for _, event := range dir.events {
if event.firstModTime.Before(firstModTime) {
firstModTime = event.firstModTime
}
}
return firstModTime
}
func (dir *eventDir) eventType() fs.EventType {
if dir.childCount() == 0 {
panic("bug: eventType must not be used on empty eventDir")
}
var evType fs.EventType
for _, childDir := range dir.dirs {
evType |= childDir.eventType()
if evType == fs.Mixed {
return fs.Mixed
}
}
for _, event := range dir.events {
evType |= event.evType
if evType == fs.Mixed {
return fs.Mixed
}
}
return evType
}
type aggregator struct {
// folderID never changes and is accessed in CommitConfiguration, which
// asynchronously updates folderCfg -> can't use folderCfg.ID (racy)
folderID string
folderCfg config.FolderConfiguration
folderCfgUpdate chan config.FolderConfiguration
// Time after which an event is scheduled for scanning when no modifications occur.
notifyDelay time.Duration
// Time after which an event is scheduled for scanning even though modifications occur.
notifyTimeout time.Duration
notifyTimer *time.Timer
notifyTimerNeedsReset bool
notifyTimerResetChan chan time.Duration
counts map[fs.EventType]int
root *eventDir
ctx context.Context
}
func newAggregator(folderCfg config.FolderConfiguration, ctx context.Context) *aggregator {
a := &aggregator{
folderID: folderCfg.ID,
folderCfgUpdate: make(chan config.FolderConfiguration),
notifyTimerNeedsReset: false,
notifyTimerResetChan: make(chan time.Duration),
counts: make(map[fs.EventType]int),
root: newEventDir(),
ctx: ctx,
}
a.updateConfig(folderCfg)
return a
}
func Aggregate(in <-chan fs.Event, out chan<- []string, folderCfg config.FolderConfiguration, cfg config.Wrapper, ctx context.Context) {
a := newAggregator(folderCfg, ctx)
// Necessary for unit tests where the backend is mocked
go a.mainLoop(in, out, cfg)
}
func (a *aggregator) mainLoop(in <-chan fs.Event, out chan<- []string, cfg config.Wrapper) {
a.notifyTimer = time.NewTimer(a.notifyDelay)
defer a.notifyTimer.Stop()
inProgressItemSubscription := events.Default.Subscribe(events.ItemStarted | events.ItemFinished)
defer events.Default.Unsubscribe(inProgressItemSubscription)
cfg.Subscribe(a)
defer cfg.Unsubscribe(a)
inProgress := make(map[string]struct{})
for {
select {
case event := <-in:
a.newEvent(event, inProgress)
case event := <-inProgressItemSubscription.C():
updateInProgressSet(event, inProgress)
case <-a.notifyTimer.C:
a.actOnTimer(out)
case interval := <-a.notifyTimerResetChan:
a.resetNotifyTimer(interval)
case folderCfg := <-a.folderCfgUpdate:
a.updateConfig(folderCfg)
case <-a.ctx.Done():
l.Debugln(a, "Stopped")
return
}
}
}
func (a *aggregator) newEvent(event fs.Event, inProgress map[string]struct{}) {
if _, ok := a.root.events["."]; ok {
l.Debugln(a, "Will scan entire folder anyway; dropping:", event.Name)
return
}
if _, ok := inProgress[event.Name]; ok {
l.Debugln(a, "Skipping path we modified:", event.Name)
return
}
a.aggregateEvent(event, time.Now())
}
func (a *aggregator) aggregateEvent(event fs.Event, evTime time.Time) {
if event.Name == "." || a.eventCount() == maxFiles {
l.Debugln(a, "Scan entire folder")
firstModTime := evTime
if a.root.childCount() != 0 {
event.Type = event.Type.Merge(a.root.eventType())
firstModTime = a.root.firstModTime()
}
a.root.dirs = make(map[string]*eventDir)
a.root.events = make(map[string]*aggregatedEvent)
a.root.events["."] = &aggregatedEvent{
firstModTime: firstModTime,
lastModTime: evTime,
evType: event.Type,
}
a.counts = make(map[fs.EventType]int)
a.counts[event.Type]++
a.resetNotifyTimerIfNeeded()
return
}
parentDir := a.root
// Check if any parent directory is already tracked or will exceed
// events per directory limit bottom up
pathSegments := strings.Split(filepath.ToSlash(event.Name), "/")
// As root dir cannot be further aggregated, allow up to maxFiles
// children.
localMaxFilesPerDir := maxFiles
var currPath string
for i, name := range pathSegments[:len(pathSegments)-1] {
currPath = filepath.Join(currPath, name)
if ev, ok := parentDir.events[name]; ok {
ev.lastModTime = evTime
if merged := event.Type.Merge(ev.evType); ev.evType != merged {
a.counts[ev.evType]--
ev.evType = merged
a.counts[ev.evType]++
}
l.Debugf("%v Parent %s (type %s) already tracked: %s", a, currPath, ev.evType, event.Name)
return
}
if parentDir.childCount() == localMaxFilesPerDir {
l.Debugf("%v Parent dir %s already has %d children, tracking it instead: %s", a, currPath, localMaxFilesPerDir, event.Name)
event.Name = filepath.Dir(currPath)
a.aggregateEvent(event, evTime)
return
}
// If there are no events below path, but we need to recurse
// into that path, create eventDir at path.
if newParent, ok := parentDir.dirs[name]; ok {
parentDir = newParent
} else {
l.Debugln(a, "Creating eventDir at:", currPath)
newParent = newEventDir()
parentDir.dirs[name] = newParent
parentDir = newParent
}
// Reset allowed children count to maxFilesPerDir for non-root
if i == 0 {
localMaxFilesPerDir = maxFilesPerDir
}
}
name := pathSegments[len(pathSegments)-1]
if ev, ok := parentDir.events[name]; ok {
ev.lastModTime = evTime
if merged := event.Type.Merge(ev.evType); ev.evType != merged {
a.counts[ev.evType]--
ev.evType = merged
a.counts[ev.evType]++
}
l.Debugf("%v Already tracked (type %v): %s", a, ev.evType, event.Name)
return
}
childDir, ok := parentDir.dirs[name]
// If a dir existed at path, it would be removed from dirs, thus
// childCount would not increase.
if !ok && parentDir.childCount() == localMaxFilesPerDir {
l.Debugf("%v Parent dir already has %d children, tracking it instead: %s", a, localMaxFilesPerDir, event.Name)
event.Name = filepath.Dir(event.Name)
a.aggregateEvent(event, evTime)
return
}
firstModTime := evTime
if ok {
firstModTime = childDir.firstModTime()
if merged := event.Type.Merge(childDir.eventType()); event.Type != merged {
a.counts[event.Type]--
event.Type = merged
}
delete(parentDir.dirs, name)
}
l.Debugf("%v Tracking (type %v): %s", a, event.Type, event.Name)
parentDir.events[name] = &aggregatedEvent{
firstModTime: firstModTime,
lastModTime: evTime,
evType: event.Type,
}
a.counts[event.Type]++
a.resetNotifyTimerIfNeeded()
}
func (a *aggregator) resetNotifyTimerIfNeeded() {
if a.notifyTimerNeedsReset {
a.resetNotifyTimer(a.notifyDelay)
}
}
// resetNotifyTimer should only ever be called when notifyTimer has stopped
// and notifyTimer.C been read from. Otherwise, call resetNotifyTimerIfNeeded.
func (a *aggregator) resetNotifyTimer(duration time.Duration) {
l.Debugln(a, "Resetting notifyTimer to", duration.String())
a.notifyTimerNeedsReset = false
a.notifyTimer.Reset(duration)
}
func (a *aggregator) actOnTimer(out chan<- []string) {
c := a.eventCount()
if c == 0 {
l.Debugln(a, "No tracked events, waiting for new event.")
a.notifyTimerNeedsReset = true
return
}
oldEvents := make(map[string]*aggregatedEvent, c)
a.popOldEventsTo(oldEvents, a.root, ".", time.Now(), true)
if a.notifyDelay != a.notifyTimeout && a.counts[fs.NonRemove] == 0 && a.counts[fs.Remove]+a.counts[fs.Mixed] != 0 {
// Only delayed events remaining, no need to delay them additionally
a.popOldEventsTo(oldEvents, a.root, ".", time.Now(), false)
}
if len(oldEvents) == 0 {
l.Debugln(a, "No old fs events")
a.resetNotifyTimer(a.notifyDelay)
return
}
// Sending to channel might block for a long time, but we need to keep
// reading from notify backend channel to avoid overflow
go a.notify(oldEvents, out)
}
// Schedule scan for given events dispatching deletes last and reset notification
// afterwards to set up for the next scan scheduling.
func (a *aggregator) notify(oldEvents map[string]*aggregatedEvent, out chan<- []string) {
timeBeforeSending := time.Now()
l.Debugf("%v Notifying about %d fs events", a, len(oldEvents))
separatedBatches := make(map[fs.EventType][]string)
for path, event := range oldEvents {
separatedBatches[event.evType] = append(separatedBatches[event.evType], path)
}
for _, evType := range [3]fs.EventType{fs.NonRemove, fs.Mixed, fs.Remove} {
currBatch := separatedBatches[evType]
if len(currBatch) != 0 {
select {
case out <- currBatch:
case <-a.ctx.Done():
return
}
}
}
// If sending to channel blocked for a long time,
// shorten next notifyDelay accordingly.
duration := time.Since(timeBeforeSending)
buffer := time.Millisecond
var nextDelay time.Duration
switch {
case duration < a.notifyDelay/10:
nextDelay = a.notifyDelay
case duration+buffer > a.notifyDelay:
nextDelay = buffer
default:
nextDelay = a.notifyDelay - duration
}
select {
case a.notifyTimerResetChan <- nextDelay:
case <-a.ctx.Done():
}
}
// popOldEvents finds events that should be scheduled for scanning recursively in dirs,
// removes those events and empty eventDirs and returns a map with all the removed
// events referenced by their filesystem path
func (a *aggregator) popOldEventsTo(to map[string]*aggregatedEvent, dir *eventDir, dirPath string, currTime time.Time, delayRem bool) {
for childName, childDir := range dir.dirs {
a.popOldEventsTo(to, childDir, filepath.Join(dirPath, childName), currTime, delayRem)
if childDir.childCount() == 0 {
delete(dir.dirs, childName)
}
}
for name, event := range dir.events {
if a.isOld(event, currTime, delayRem) {
to[filepath.Join(dirPath, name)] = event
delete(dir.events, name)
a.counts[event.evType]--
}
}
}
func (a *aggregator) isOld(ev *aggregatedEvent, currTime time.Time, delayRem bool) bool {
// Deletes should in general be scanned last, therefore they are delayed by
// letting them time out. This behaviour is overriden by delayRem == false.
// Refer to following comments as to why.
// An event that has not registered any new modifications recently is scanned.
// a.notifyDelay is the user facing value signifying the normal delay between
// picking up a modification and scanning it. As scheduling scans happens at
// regular intervals of a.notifyDelay the delay of a single event is not exactly
// a.notifyDelay, but lies in the range of 0.5 to 1.5 times a.notifyDelay.
if (!delayRem || ev.evType == fs.NonRemove) && 2*currTime.Sub(ev.lastModTime) > a.notifyDelay {
return true
}
// When an event registers repeat modifications or involves removals it
// is delayed to reduce resource usage, but after a certain time (notifyTimeout)
// passed it is scanned anyway.
// If only removals are remaining to be scanned, there is no point to delay
// removals further, so this behaviour is overriden by delayRem == false.
return currTime.Sub(ev.firstModTime) > a.notifyTimeout
}
func (a *aggregator) eventCount() int {
c := 0
for _, v := range a.counts {
c += v
}
return c
}
func (a *aggregator) String() string {
return fmt.Sprintf("aggregator/%s:", a.folderCfg.Description())
}
func (a *aggregator) VerifyConfiguration(from, to config.Configuration) error {
return nil
}
func (a *aggregator) CommitConfiguration(from, to config.Configuration) bool {
for _, folderCfg := range to.Folders {
if folderCfg.ID == a.folderID {
select {
case a.folderCfgUpdate <- folderCfg:
case <-a.ctx.Done():
}
return true
}
}
// Nothing to do, model will soon stop this
return true
}
func (a *aggregator) updateConfig(folderCfg config.FolderConfiguration) {
a.notifyDelay = time.Duration(folderCfg.FSWatcherDelayS) * time.Second
a.notifyTimeout = notifyTimeout(folderCfg.FSWatcherDelayS)
a.folderCfg = folderCfg
}
func updateInProgressSet(event events.Event, inProgress map[string]struct{}) {
if event.Type == events.ItemStarted {
path := event.Data.(map[string]string)["item"]
inProgress[path] = struct{}{}
} else if event.Type == events.ItemFinished {
path := event.Data.(map[string]interface{})["item"].(string)
delete(inProgress, path)
}
}
// Events that involve removals or continuously receive new modifications are
// delayed but must time out at some point. The following numbers come out of thin
// air, they were just considered as a sensible compromise between fast updates and
// saving resources. For short delays the timeout is 6 times the delay, capped at 1
// minute. For delays longer than 1 minute, the delay and timeout are equal.
func notifyTimeout(eventDelayS int) time.Duration {
shortDelayS := 10
shortDelayMultiplicator := 6
longDelayS := 60
longDelayTimeout := time.Duration(1) * time.Minute
if eventDelayS < shortDelayS {
return time.Duration(eventDelayS*shortDelayMultiplicator) * time.Second
}
if eventDelayS < longDelayS {
return longDelayTimeout
}
return time.Duration(eventDelayS) * time.Second
}