Merge pull request #10355 from hashicorp/dnephin/stream-fix-topic-head-bug

stream: fix a bug with subscriptions and the latest item in the topic buffers.
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Daniel Nephin 2021-06-07 17:27:57 -04:00 committed by GitHub
commit 8fbbe036e0
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5 changed files with 26 additions and 38 deletions

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@ -81,7 +81,7 @@ func (b *eventBuffer) Append(events []Event) {
b.AppendItem(newBufferItem(events))
}
// AppendBuffer joins another buffer which may be the tail of a separate buffer
// AppendItem joins another buffer which may be the tail of a separate buffer
// for example a buffer that's had the events from a snapshot appended may
// finally by linked to the topic buffer for the subsequent events so
// subscribers can seamlessly consume the updates. Note that Events in item must
@ -194,27 +194,19 @@ func (i *bufferItem) Next(ctx context.Context, closed <-chan struct{}) (*bufferI
return next, nil
}
// NextNoBlock returns the next item in the buffer without blocking. If it
// reaches the most recent item it will return nil.
func (i *bufferItem) NextNoBlock() *bufferItem {
// NextNoBlock returns true and the next item in the buffer without blocking.
// If there are no subsequent items it returns false and an empty item.
// The empty item will be ignored by subscribers, but has the same link as this
// bufferItem without the Events.
// When the link.ch of the empty item is closed, subscriptions are notified of
// the next item.
func (i *bufferItem) NextNoBlock() (*bufferItem, bool) {
nextRaw := i.link.next.Load()
if nextRaw == nil {
return nil
}
return nextRaw.(*bufferItem)
}
// NextLink returns either the next item in the buffer if there is one, or
// an empty item (that will be ignored by subscribers) that has a pointer to
// the same link as this bufferItem (but none of the bufferItem content).
// When the link.ch is closed, subscriptions will be notified of the next item.
func (i *bufferItem) NextLink() *bufferItem {
next := i.NextNoBlock()
if next == nil {
// Return an empty item that can be followed to the next item published.
return &bufferItem{link: i.link}
return &bufferItem{link: i.link}, false
}
return next
return nextRaw.(*bufferItem), true
}
// HasEventIndex returns true if index matches the Event.Index of this item. Returns

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@ -17,10 +17,6 @@ func TestEventBufferFuzz(t *testing.T) {
t.Skip("too slow for testing.Short")
}
if testing.Short() {
t.Skip("too slow for short run")
}
nReaders := 1000
nMessages := 1000

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@ -171,7 +171,8 @@ func (e *EventPublisher) Subscribe(req *SubscribeRequest) (*Subscription, error)
subscriptionHead := buf.Head()
// splice the rest of the topic buffer onto the subscription buffer so
// the subscription will receive new events.
buf.AppendItem(topicHead.NextLink())
next, _ := topicHead.NextNoBlock()
buf.AppendItem(next)
return e.subscriptions.add(req, subscriptionHead), nil
}

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@ -49,34 +49,33 @@ func (s *eventSnapshot) appendAndSplice(req SubscribeRequest, fn SnapshotFunc, t
func (s *eventSnapshot) spliceFromTopicBuffer(topicBufferHead *bufferItem, idx uint64) {
item := topicBufferHead
for {
next := item.NextNoBlock()
switch {
case next == nil:
// This is the head of the topic buffer (or was just now which is after
// the snapshot completed). We don't want any of the events (if any) in
// the snapshot buffer as they came before the snapshot but we do need to
// wait for the next update.
s.buffer.AppendItem(item.NextLink())
return
case next.Err != nil:
case item.Err != nil:
// This case is not currently possible because errors can only come
// from a snapshot func, and this is consuming events from a topic
// buffer which does not contain a snapshot.
// Handle this case anyway in case errors can come from other places
// in the future.
s.buffer.AppendItem(next)
s.buffer.AppendItem(item)
return
case len(next.Events) > 0 && next.Events[0].Index > idx:
case len(item.Events) > 0 && item.Events[0].Index > idx:
// We've found an update in the topic buffer that happened after our
// snapshot was taken, splice it into the snapshot buffer so subscribers
// can continue to read this and others after it.
s.buffer.AppendItem(next)
s.buffer.AppendItem(item)
return
}
// We don't need this item, continue to next
next, ok := item.NextNoBlock()
if !ok {
// We reached the head of the topic buffer. We don't want any of the
// events in the topic buffer as they came before the snapshot.
// Append a link to any future items.
s.buffer.AppendItem(next)
return
}
// Proceed to the next item in the topic buffer
item = next
}
}

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@ -95,7 +95,7 @@ func TestEventSnapshot(t *testing.T) {
// be appended before the snapshot fn executes in another goroutine since
// it's operating an a possible stale "snapshot". This is the same as
// reality with the state store where updates that occur after the
// snapshot is taken but while the SnapFnis still running must be captured
// snapshot is taken but while the SnapFn is still running must be captured
// correctly.
for i := 0; i < tc.updatesAfterSnap; i++ {
index := snapIndex + 1 + uint64(i)