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MIN12352
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codeparrot

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// NewIndexSubscriber creates a new index subscriber. It also starts the
// handler for incoming index update subscriptions.
func NewIndexSubscriber(sCtx context.Context) *IndexSubscriber {
ctx, cancel := context.WithCancel(sCtx)
s := &IndexSubscriber{
c: make(chan IndexNtfn, bufferSize),
subscriptions: make(map[string]*IndexSubscription),
ctx: ctx,
cancel: cancel,
quit: make(chan struct{}),
}
return s
}
// Subscribe subscribes an index for updates. The returned index subscription
// has functions to retrieve a channel that produces a stream of index updates
// and to stop the stream when the caller no longer wishes to receive updates.
func (s *IndexSubscriber) Subscribe(index Indexer, prerequisite string) (*IndexSubscription, error) {
sub := newIndexSubscription(s, index, prerequisite)
// If the subscription has a prequisite, find it and set the subscription
// as a dependency.
if prerequisite != noPrereqs {
s.mtx.Lock()
prereq, ok := s.subscriptions[prerequisite]
s.mtx.Unlock()
if !ok {
return nil, fmt.Errorf(""no subscription found with id %s"", prerequisite)
}
prereq.mtx.Lock()
defer prereq.mtx.Unlock()
if prereq.dependent != nil {
return nil, fmt.Errorf(""%s already has a dependent set: %s"",
prereq.id, prereq.dependent.id)
}
prereq.dependent = sub
atomic.AddUint32(&s.subscribers, 1)
return sub, nil
}
// If the subscription does not have a prerequisite, add it to the index
// subscriber's subscriptions.
s.mtx.Lock()
s.subscriptions[sub.id] = sub
s.mtx.Unlock()
atomic.AddUint32(&s.subscribers, 1)
return sub, nil
}
// Notify relays an index notification to subscribed indexes for processing.
func (s *IndexSubscriber) Notify(ntfn *IndexNtfn) {
subscribers := atomic.LoadUint32(&s.subscribers)
// Only relay notifications when there are subscribed indexes
// to be notified.
if subscribers > 0 {
select {
case <-s.quit:
case s.c <- *ntfn:
}
}
}
// findLowestIndexTipHeight determines the lowest index tip height among
// subscribed indexes and their dependencies.
func (s *IndexSubscriber) findLowestIndexTipHeight(queryer ChainQueryer) (int64, int64, error) {
// Find the lowest tip height to catch up among subscribed indexes.
bestHeight, _ := queryer.Best()
lowestHeight := bestHeight
for _, sub := range s.subscriptions {
tipHeight, tipHash, err := sub.idx.Tip()
if err != nil {
return 0, bestHeight, err
}
// Ensure the index tip is on the main chain.
if !queryer.MainChainHasBlock(tipHash) {
return 0, bestHeight, fmt.Errorf(""%s: index tip (%s) is not on the ""+
""main chain"", sub.idx.Name(), tipHash)
}
if tipHeight < lowestHeight {
lowestHeight = tipHeight
}
// Update the lowest tip height if a dependent has a lower tip height.
dependent := sub.dependent
for dependent != nil {
tipHeight, _, err := sub.dependent.idx.Tip()
if err != nil {
return 0, bestHeight, err
}
if tipHeight < lowestHeight {