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events.go
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events.go
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package events
import (
"context"
"errors"
"fmt"
"sync"
"time"
comatproto "github.com/bluesky-social/indigo/api/atproto"
"github.com/bluesky-social/indigo/models"
"github.com/prometheus/client_golang/prometheus"
logging "github.com/ipfs/go-log"
"go.opentelemetry.io/otel"
)
var log = logging.Logger("events")
type Scheduler interface {
AddWork(ctx context.Context, repo string, val *XRPCStreamEvent) error
Shutdown()
}
type EventManager struct {
subs []*Subscriber
subsLk sync.Mutex
bufferSize int
persister EventPersistence
}
func NewEventManager(persister EventPersistence) *EventManager {
em := &EventManager{
bufferSize: 32 << 10,
persister: persister,
}
persister.SetEventBroadcaster(em.broadcastEvent)
return em
}
const (
opSubscribe = iota
opUnsubscribe
opSend
)
type Operation struct {
op int
sub *Subscriber
evt *XRPCStreamEvent
}
func (em *EventManager) Shutdown(ctx context.Context) error {
return em.persister.Shutdown(ctx)
}
func (em *EventManager) broadcastEvent(evt *XRPCStreamEvent) {
em.subsLk.Lock()
defer em.subsLk.Unlock()
// TODO: for a larger fanout we should probably have dedicated goroutines
// for subsets of the subscriber set, and tiered channels to distribute
// events out to them, or some similar architecture
// Alternatively, we might just want to not allow too many subscribers
// directly to the bgs, and have rebroadcasting proxies instead
for _, s := range em.subs {
if s.filter(evt) {
s.enqueuedCounter.Inc()
select {
case s.outgoing <- evt:
case <-s.done:
default:
log.Warnw("dropping slow consumer due to event overflow", "bufferSize", len(s.outgoing), "ident", s.ident)
go func(torem *Subscriber) {
torem.lk.Lock()
if !torem.cleanedUp {
select {
case torem.outgoing <- &XRPCStreamEvent{
Error: &ErrorFrame{
Error: "ConsumerTooSlow",
},
}:
case <-time.After(time.Second * 5):
log.Warnw("failed to send error frame to backed up consumer", "ident", torem.ident)
}
}
torem.lk.Unlock()
torem.cleanup()
}(s)
}
s.broadcastCounter.Inc()
}
}
}
func (em *EventManager) persistAndSendEvent(ctx context.Context, evt *XRPCStreamEvent) {
// TODO: can cut 5-10% off of disk persister benchmarks by making this function
// accept a uid. The lookup inside the persister is notably expensive (despite
// being an lru cache?)
if err := em.persister.Persist(ctx, evt); err != nil {
log.Errorf("failed to persist outbound event: %s", err)
}
}
type Subscriber struct {
outgoing chan *XRPCStreamEvent
filter func(*XRPCStreamEvent) bool
done chan struct{}
cleanup func()
lk sync.Mutex
cleanedUp bool
ident string
enqueuedCounter prometheus.Counter
broadcastCounter prometheus.Counter
}
const (
EvtKindErrorFrame = -1
EvtKindMessage = 1
)
type EventHeader struct {
Op int64 `cborgen:"op"`
MsgType string `cborgen:"t"`
}
type XRPCStreamEvent struct {
Error *ErrorFrame
RepoCommit *comatproto.SyncSubscribeRepos_Commit
RepoHandle *comatproto.SyncSubscribeRepos_Handle
RepoIdentity *comatproto.SyncSubscribeRepos_Identity
RepoInfo *comatproto.SyncSubscribeRepos_Info
RepoMigrate *comatproto.SyncSubscribeRepos_Migrate
RepoTombstone *comatproto.SyncSubscribeRepos_Tombstone
LabelLabels *comatproto.LabelSubscribeLabels_Labels
LabelInfo *comatproto.LabelSubscribeLabels_Info
// some private fields for internal routing perf
PrivUid models.Uid `json:"-" cborgen:"-"`
PrivPdsId uint `json:"-" cborgen:"-"`
PrivRelevantPds []uint `json:"-" cborgen:"-"`
}
type ErrorFrame struct {
Error string `cborgen:"error"`
Message string `cborgen:"message"`
}
func (em *EventManager) AddEvent(ctx context.Context, ev *XRPCStreamEvent) error {
ctx, span := otel.Tracer("events").Start(ctx, "AddEvent")
defer span.End()
em.persistAndSendEvent(ctx, ev)
return nil
}
var (
ErrPlaybackShutdown = fmt.Errorf("playback shutting down")
ErrCaughtUp = fmt.Errorf("caught up")
)
func (em *EventManager) Subscribe(ctx context.Context, ident string, filter func(*XRPCStreamEvent) bool, since *int64) (<-chan *XRPCStreamEvent, func(), error) {
if filter == nil {
filter = func(*XRPCStreamEvent) bool { return true }
}
done := make(chan struct{})
sub := &Subscriber{
ident: ident,
outgoing: make(chan *XRPCStreamEvent, em.bufferSize),
filter: filter,
done: done,
enqueuedCounter: eventsEnqueued.WithLabelValues(ident),
broadcastCounter: eventsBroadcast.WithLabelValues(ident),
}
sub.cleanup = sync.OnceFunc(func() {
sub.lk.Lock()
defer sub.lk.Unlock()
close(done)
em.rmSubscriber(sub)
close(sub.outgoing)
sub.cleanedUp = true
})
if since == nil {
em.addSubscriber(sub)
return sub.outgoing, sub.cleanup, nil
}
out := make(chan *XRPCStreamEvent, em.bufferSize)
go func() {
lastSeq := *since
// run playback to get through *most* of the events, getting our current cursor close to realtime
if err := em.persister.Playback(ctx, *since, func(e *XRPCStreamEvent) error {
select {
case <-done:
return ErrPlaybackShutdown
case out <- e:
seq := sequenceForEvent(e)
if seq > 0 {
lastSeq = seq
}
return nil
}
}); err != nil {
if errors.Is(err, ErrPlaybackShutdown) {
log.Warnf("events playback: %s", err)
} else {
log.Errorf("events playback: %s", err)
}
// TODO: send an error frame or something?
close(out)
return
}
// now, start buffering events from the live stream
em.addSubscriber(sub)
first := <-sub.outgoing
// run playback again to get us to the events that have started buffering
if err := em.persister.Playback(ctx, lastSeq, func(e *XRPCStreamEvent) error {
seq := sequenceForEvent(e)
if seq > sequenceForEvent(first) {
return ErrCaughtUp
}
select {
case <-done:
return ErrPlaybackShutdown
case out <- e:
return nil
}
}); err != nil {
if !errors.Is(err, ErrCaughtUp) {
log.Errorf("events playback: %s", err)
// TODO: send an error frame or something?
close(out)
em.rmSubscriber(sub)
return
}
}
// now that we are caught up, just copy events from the channel over
for evt := range sub.outgoing {
select {
case out <- evt:
case <-done:
em.rmSubscriber(sub)
return
}
}
}()
return out, sub.cleanup, nil
}
func sequenceForEvent(evt *XRPCStreamEvent) int64 {
switch {
case evt == nil:
return -1
case evt.RepoCommit != nil:
return evt.RepoCommit.Seq
case evt.RepoHandle != nil:
return evt.RepoHandle.Seq
case evt.RepoMigrate != nil:
return evt.RepoMigrate.Seq
case evt.RepoTombstone != nil:
return evt.RepoTombstone.Seq
case evt.RepoIdentity != nil:
return evt.RepoIdentity.Seq
case evt.RepoInfo != nil:
return -1
case evt.Error != nil:
return -1
default:
return -1
}
}
func (em *EventManager) rmSubscriber(sub *Subscriber) {
em.subsLk.Lock()
defer em.subsLk.Unlock()
for i, s := range em.subs {
if s == sub {
em.subs[i] = em.subs[len(em.subs)-1]
em.subs = em.subs[:len(em.subs)-1]
break
}
}
}
func (em *EventManager) addSubscriber(sub *Subscriber) {
em.subsLk.Lock()
defer em.subsLk.Unlock()
em.subs = append(em.subs, sub)
}
func (em *EventManager) TakeDownRepo(ctx context.Context, user models.Uid) error {
return em.persister.TakeDownRepo(ctx, user)
}