// Returns the (ordered) union of all of the changes made to multiple channels.
func (db *Database) VectorMultiChangesFeed(chans base.Set, options ChangesOptions) (<-chan *ChangeEntry, error) {
to := ""
var userVbNo uint16
if db.user != nil && db.user.Name() != "" {
to = fmt.Sprintf(" (to %s)", db.user.Name())
userVbNo = uint16(db.Bucket.VBHash(db.user.DocID()))
}
base.LogTo("Changes+", "Vector MultiChangesFeed(%s, %+v) ... %s", chans, options, to)
output := make(chan *ChangeEntry, 50)
go func() {
var cumulativeClock *base.SyncSequenceClock
var lastHashedValue string
hashedEntryCount := 0
defer func() {
base.LogTo("Changes+", "MultiChangesFeed done %s", to)
close(output)
}()
var changeWaiter *changeWaiter
var userCounter uint64 // Wait counter used to identify changes to the user document
var addedChannels base.Set // Tracks channels added to the user during changes processing.
var userChanged bool // Whether the user document has changed
// Restrict to available channels, expand wild-card, and find since when these channels
// have been available to the user:
var channelsSince channels.TimedSet
if db.user != nil {
channelsSince = db.user.FilterToAvailableChannels(chans)
} else {
channelsSince = channels.AtSequence(chans, 0)
}
if options.Wait {
changeWaiter = db.startChangeWaiter(channelsSince.AsSet())
userCounter = changeWaiter.CurrentUserCount()
db.initializePrincipalPolling(changeWaiter.GetUserKeys())
}
cumulativeClock = base.NewSyncSequenceClock()
cumulativeClock.SetTo(getChangesClock(options.Since))
// This loop is used to re-run the fetch after every database change, in Wait mode
outer:
for {
// Get the last polled stable sequence. We don't return anything later than stable sequence in each iteration
stableClock, err := db.changeCache.GetStableClock(true)
if err != nil {
base.Warn("MultiChangesFeed got error reading stable sequence: %v", err)
return
}
// Updates the changeWaiter to the current set of available channels.
if changeWaiter != nil {
changeWaiter.UpdateChannels(channelsSince)
}
base.LogTo("Changes+", "MultiChangesFeed: channels expand to %#v ... %s", channelsSince.String(), to)
// Build the channel feeds.
feeds, err := db.initializeChannelFeeds(channelsSince, options, addedChannels, userVbNo)
if err != nil {
return
}
// This loop reads the available entries from all the feeds in parallel, merges them,
// and writes them to the output channel:
current := make([]*ChangeEntry, len(feeds))
var sentSomething bool
nextEntry := getNextSequenceFromFeeds(current, feeds)
for {
minEntry := nextEntry
if minEntry == nil {
break // Exit the loop when there are no more entries
}
// Calculate next entry here, to help identify whether minEntry is the last entry we're sending,
// to guarantee hashing
nextEntry = getNextSequenceFromFeeds(current, feeds)
if options.ActiveOnly {
if minEntry.Deleted || minEntry.allRemoved {
continue
}
}
// Don't send any entries later than the stable sequence
if stableClock.GetSequence(minEntry.Seq.vbNo) < minEntry.Seq.Seq {
continue
}
// Add the doc body or the conflicting rev IDs, if those options are set:
if options.IncludeDocs || options.Conflicts {
db.addDocToChangeEntry(minEntry, options)
}
// Clock handling
if minEntry.Seq.TriggeredBy == 0 {
// Update the cumulative clock, and stick it on the entry.
cumulativeClock.SetMaxSequence(minEntry.Seq.vbNo, minEntry.Seq.Seq)
// Force new hash generation for non-continuous changes feeds if this is the last entry to be sent - either
// because there are no more entries in the channel feeds, or we're going to hit the limit.
forceHash := false
if options.Continuous == false && (nextEntry == nil || options.Limit == 1) {
forceHash = true
}
lastHashedValue = db.calculateHashWhenNeeded(
options,
minEntry,
cumulativeClock,
&hashedEntryCount,
lastHashedValue,
forceHash,
)
} else {
// For backfill (triggered by), we don't want to update the cumulative clock. All entries triggered by the
// same sequence reference the same triggered by clock, so it should only need to get hashed once.
// If this is the first entry for this triggered by, initialize the triggered by clock's
// hash value.
if minEntry.Seq.TriggeredByClock.GetHashedValue() == "" {
cumulativeClock.SetMaxSequence(minEntry.Seq.TriggeredByVbNo, minEntry.Seq.TriggeredBy)
clockHash, err := db.SequenceHasher.GetHash(cumulativeClock)
if err != nil {
base.Warn("Error calculating hash for triggered by clock:%v", base.PrintClock(cumulativeClock))
} else {
minEntry.Seq.TriggeredByClock.SetHashedValue(clockHash)
}
}
}
// Send the entry, and repeat the loop:
base.LogTo("Changes+", "MultiChangesFeed sending %+v %s", minEntry, to)
select {
case <-options.Terminator:
return
case output <- minEntry:
}
sentSomething = true
// Stop when we hit the limit (if any):
if options.Limit > 0 {
options.Limit--
if options.Limit == 0 {
break outer
}
}
}
if !options.Continuous && (sentSomething || changeWaiter == nil) {
break
}
// Update options.Since for use in the next outer loop iteration.
options.Since.Clock = cumulativeClock
// If nothing found, and in wait mode: wait for the db to change, then run again.
// First notify the reader that we're waiting by sending a nil.
base.LogTo("Changes+", "MultiChangesFeed waiting... %s", to)
output <- nil
waitForChanges:
for {
waitResponse := changeWaiter.Wait()
if waitResponse == WaiterClosed {
break outer
} else if waitResponse == WaiterHasChanges {
select {
case <-options.Terminator:
return
default:
break waitForChanges
}
} else if waitResponse == WaiterCheckTerminated {
// Check whether I was terminated while waiting for a change. If not, resume wait.
select {
case <-options.Terminator:
return
default:
}
}
}
// Before checking again, update the User object in case its channel access has
// changed while waiting:
userChanged, userCounter, addedChannels, err = db.checkForUserUpdates(userCounter, changeWaiter)
if userChanged && db.user != nil {
channelsSince = db.user.FilterToAvailableChannels(chans)
}
if err != nil {
change := makeErrorEntry("User not found during reload - terminating changes feed")
base.LogTo("Changes+", "User not found during reload - terminating changes feed with entry %+v", change)
output <- &change
return
}
}
}()
return output, nil
}
// Returns the (ordered) union of all of the changes made to multiple channels.
func (db *Database) SimpleMultiChangesFeed(chans base.Set, options ChangesOptions) (<-chan *ChangeEntry, error) {
to := ""
if db.user != nil && db.user.Name() != "" {
to = fmt.Sprintf(" (to %s)", db.user.Name())
}
base.LogTo("Changes", "MultiChangesFeed(%s, %+v) ... %s", chans, options, to)
output := make(chan *ChangeEntry, 50)
go func() {
defer func() {
base.LogTo("Changes", "MultiChangesFeed done %s", to)
close(output)
}()
var changeWaiter *changeWaiter
var lowSequence uint64
var lateSequenceFeeds map[string]*lateSequenceFeed
var userCounter uint64 // Wait counter used to identify changes to the user document
var addedChannels base.Set // Tracks channels added to the user during changes processing.
var userChanged bool // Whether the user document has changed in a given iteration loop
// lowSequence is used to send composite keys to clients, so that they can obtain any currently
// skipped sequences in a future iteration or request.
oldestSkipped := db.changeCache.getOldestSkippedSequence()
if oldestSkipped > 0 {
lowSequence = oldestSkipped - 1
} else {
lowSequence = 0
}
// Restrict to available channels, expand wild-card, and find since when these channels
// have been available to the user:
var channelsSince channels.TimedSet
if db.user != nil {
channelsSince = db.user.FilterToAvailableChannels(chans)
} else {
channelsSince = channels.AtSequence(chans, 0)
}
if options.Wait {
options.Wait = false
changeWaiter = db.startChangeWaiter(channelsSince.AsSet())
userCounter = changeWaiter.CurrentUserCount()
}
// If a request has a low sequence that matches the current lowSequence,
// ignore the low sequence. This avoids infinite looping of the records between
// low::high. It also means any additional skipped sequences between low::high won't
// be sent until low arrives or is abandoned.
if options.Since.LowSeq != 0 && options.Since.LowSeq == lowSequence {
options.Since.LowSeq = 0
}
// For a continuous feed, initialise the lateSequenceFeeds that track late-arriving sequences
// to the channel caches.
if options.Continuous {
lateSequenceFeeds = make(map[string]*lateSequenceFeed)
}
// This loop is used to re-run the fetch after every database change, in Wait mode
outer:
for {
// Updates the changeWaiter to the current set of available channels
if changeWaiter != nil {
changeWaiter.UpdateChannels(channelsSince)
}
base.LogTo("Changes+", "MultiChangesFeed: channels expand to %#v ... %s", channelsSince, to)
// lowSequence is used to send composite keys to clients, so that they can obtain any currently
// skipped sequences in a future iteration or request.
oldestSkipped = db.changeCache.getOldestSkippedSequence()
if oldestSkipped > 0 {
lowSequence = oldestSkipped - 1
} else {
lowSequence = 0
}
// Populate the parallel arrays of channels and names:
feeds := make([]<-chan *ChangeEntry, 0, len(channelsSince))
names := make([]string, 0, len(channelsSince))
// Get read lock for late-arriving sequences, to avoid sending the same late arrival in
// two different changes iterations. e.g. without the RLock, a late-arriving sequence
// could be written to channel X during one iteration, and channel Y during another. Users
// with access to both channels would see two versions on the feed.
for name, vbSeqAddedAt := range channelsSince {
chanOpts := options
seqAddedAt := vbSeqAddedAt.Sequence
// Check whether requires backfill based on addedChannels in this _changes feed
isNewChannel := false
if addedChannels != nil {
_, isNewChannel = addedChannels[name]
}
// Check whether requires backfill based on current sequence, seqAddedAt
// Triggered by handling:
// 1. options.Since.TriggeredBy == seqAddedAt : We're in the middle of backfill for this channel, based
// on the access grant in sequence options.Since.TriggeredBy. Normally the entire backfill would be done in one
// changes feed iteration, but this can be split over multiple iterations when 'limit' is used.
// 2. options.Since.TriggeredBy == 0 : Not currently doing a backfill
// 3. options.Since.TriggeredBy != 0 and <= seqAddedAt: We're in the middle of a backfill for another channel, but the backfill for
// this channel is still pending. Initiate the backfill for this channel - will be ordered below in the usual way (iterating over all channels)
// Backfill required when seqAddedAt is before current sequence
backfillRequired := seqAddedAt > 1 && options.Since.Before(SequenceID{Seq: seqAddedAt})
// Ensure backfill isn't already in progress for this seqAddedAt
backfillPending := options.Since.TriggeredBy == 0 || options.Since.TriggeredBy < seqAddedAt
if isNewChannel || (backfillRequired && backfillPending) {
// Newly added channel so initiate backfill:
chanOpts.Since = SequenceID{Seq: 0, TriggeredBy: seqAddedAt}
}
feed, err := db.changesFeed(name, chanOpts)
if err != nil {
base.Warn("MultiChangesFeed got error reading changes feed %q: %v", name, err)
return
}
feeds = append(feeds, feed)
names = append(names, name)
// Late sequence handling - for out-of-order sequences prior to options.Since that
// have arrived in the channel cache since this changes request started. Only need for
// continuous feeds - one-off changes requests only need the standard channel cache.
if options.Continuous {
lateSequenceFeedHandler := lateSequenceFeeds[name]
if lateSequenceFeedHandler != nil {
latefeed, err := db.getLateFeed(lateSequenceFeedHandler)
if err != nil {
base.Warn("MultiChangesFeed got error reading late sequence feed %q: %v", name, err)
} else {
// Mark feed as actively used in this iteration. Used to remove lateSequenceFeeds
// when the user loses channel access
lateSequenceFeedHandler.active = true
feeds = append(feeds, latefeed)
names = append(names, fmt.Sprintf("late_%s", name))
}
} else {
// Initialize lateSequenceFeeds[name] for next iteration
lateSequenceFeeds[name] = db.newLateSequenceFeed(name)
}
}
}
// If the user object has changed, create a special pseudo-feed for it:
if db.user != nil {
feeds, names = db.appendUserFeed(feeds, names, options)
}
current := make([]*ChangeEntry, len(feeds))
// This loop reads the available entries from all the feeds in parallel, merges them,
// and writes them to the output channel:
var sentSomething bool
for {
// Read more entries to fill up the current[] array:
for i, cur := range current {
if cur == nil && feeds[i] != nil {
var ok bool
current[i], ok = <-feeds[i]
if !ok {
feeds[i] = nil
}
}
}
// Find the current entry with the minimum sequence:
minSeq := MaxSequenceID
var minEntry *ChangeEntry
for _, cur := range current {
if cur != nil && cur.Seq.Before(minSeq) {
minSeq = cur.Seq
minEntry = cur
}
}
if minEntry == nil {
break // Exit the loop when there are no more entries
}
// Clear the current entries for the sequence just sent:
if minEntry.Removed != nil {
minEntry.allRemoved = true
}
for i, cur := range current {
if cur != nil && cur.Seq == minSeq {
current[i] = nil
// Track whether this is a removal from all user's channels
if cur.Removed == nil && minEntry.allRemoved == true {
minEntry.allRemoved = false
}
// Also concatenate the matching entries' Removed arrays:
if cur != minEntry && cur.Removed != nil {
if minEntry.Removed == nil {
minEntry.Removed = cur.Removed
} else {
minEntry.Removed = minEntry.Removed.Union(cur.Removed)
}
}
}
}
if options.ActiveOnly {
if minEntry.Deleted || minEntry.allRemoved {
continue
}
}
// Update options.Since for use in the next outer loop iteration. Only update
// when minSeq is greater than the previous options.Since value - we don't want to
// roll back the Since value when we get an late sequence is processed.
if options.Since.Before(minSeq) {
options.Since = minSeq
}
// Add the doc body or the conflicting rev IDs, if those options are set:
if options.IncludeDocs || options.Conflicts {
db.addDocToChangeEntry(minEntry, options)
}
// Update the low sequence on the entry we're going to send
minEntry.Seq.LowSeq = lowSequence
// Send the entry, and repeat the loop:
base.LogTo("Changes+", "MultiChangesFeed sending %+v %s", minEntry, to)
select {
case <-options.Terminator:
return
case output <- minEntry:
}
sentSomething = true
// Stop when we hit the limit (if any):
if options.Limit > 0 {
options.Limit--
if options.Limit == 0 {
break outer
}
}
}
if !options.Continuous && (sentSomething || changeWaiter == nil) {
break
}
// If nothing found, and in wait mode: wait for the db to change, then run again.
// First notify the reader that we're waiting by sending a nil.
base.LogTo("Changes+", "MultiChangesFeed waiting... %s", to)
output <- nil
waitForChanges:
for {
waitResponse := changeWaiter.Wait()
if waitResponse == WaiterClosed {
break outer
} else if waitResponse == WaiterHasChanges {
select {
case <-options.Terminator:
return
default:
break waitForChanges
}
} else if waitResponse == WaiterCheckTerminated {
// Check whether I was terminated while waiting for a change. If not, resume wait.
select {
case <-options.Terminator:
return
default:
}
}
}
// Check whether user channel access has changed while waiting:
var err error
userChanged, userCounter, addedChannels, err = db.checkForUserUpdates(userCounter, changeWaiter)
if err != nil {
change := makeErrorEntry("User not found during reload - terminating changes feed")
base.LogTo("Changes+", "User not found during reload - terminating changes feed with entry %+v", change)
output <- &change
return
}
if userChanged && db.user != nil {
channelsSince = db.user.FilterToAvailableChannels(chans)
}
// Clean up inactive lateSequenceFeeds (because user has lost access to the channel)
for channel, lateFeed := range lateSequenceFeeds {
if !lateFeed.active {
db.closeLateFeed(lateFeed)
delete(lateSequenceFeeds, channel)
} else {
lateFeed.active = false
}
}
}
}()
return output, nil
}
