func (s *GraphStore) insert(e *spb.Entry) {
i := sort.Search(len(s.entries), func(i int) bool {
return compare.Entries(e, s.entries[i]) == compare.LT
})
if i == len(s.entries) {
s.entries = append(s.entries, e)
} else if i < len(s.entries) && compare.EntriesEqual(e, s.entries[i]) {
s.entries[i] = e
} else if i == 0 {
s.entries = append([]*spb.Entry{e}, s.entries...)
} else {
s.entries = append(s.entries[:i], append([]*spb.Entry{e}, s.entries[i:]...)...)
}
}
// invoke calls req concurrently for each delegated service in p, merges the
// results, and delivers them to f.
func (p *proxyService) invoke(req func(graphstore.Service, graphstore.EntryFunc) error, f graphstore.EntryFunc) error {
stop := make(chan struct{}) // Closed to signal cancellation
// Create a channel for each delegated request, and a callback that
// delivers results to that channel. The callback will handle cancellation
// signaled by a close of the stop channel, and exit early.
rcv := make([]graphstore.EntryFunc, len(p.stores)) // callbacks
chs := make([]chan *spb.Entry, len(p.stores)) // channels
for i := range p.stores {
ch := make(chan *spb.Entry)
chs[i] = ch
rcv[i] = func(e *spb.Entry) error {
select {
case <-stop: // cancellation has been signalled
return nil
case ch <- e:
return nil
}
}
}
// Invoke the requests for each service, using the corresponding callback.
errc := p.foreach(func(i int, s graphstore.Service) error {
err := req(s, rcv[i])
close(chs[i])
return err
})
// Accumulate and merge the results. This is a straightforward round-robin
// n-finger merge of the values from the delegated requests.
var h compare.ByEntries // used to preserve stream order
var last *spb.Entry // used to deduplicate entries
var perr error // error while accumulating
go func() {
defer close(stop)
for {
hit := false // are any requests still pending?
// Give each channel a chance to produce a value, round-robin to
// preserve the global ordering.
for _, ch := range chs {
if e, ok := <-ch; ok {
hit = true
heap.Push(&h, e)
}
}
// If there are any values pending, deliver one to the consumer.
// If not, and there are no more values coming, we're finished.
if h.Len() != 0 {
entry := heap.Pop(&h).(*spb.Entry)
if last == nil || !compare.EntriesEqual(last, entry) {
last = entry
if err := f(entry); err != nil {
if err != io.EOF {
perr = err
}
return
}
}
} else if !hit {
return // no more work to do
}
}
}()
err := waitErr(errc) // wait for all receives to complete
<-stop // wait for all sends to complete
if perr != nil {
return perr
}
return err
}