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[FIXED] JetStream: stream assignment data race #4589

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merged 1 commit into from Sep 26, 2023
Merged

[FIXED] JetStream: stream assignment data race #4589

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13 changes: 11 additions & 2 deletions server/stream.go
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Expand Up @@ -404,12 +404,21 @@ func (a *Account) addStreamWithAssignment(config *StreamConfig, fsConfig *FileSt
}

// Make sure we are ok when these are done in parallel.
v, loaded := jsa.inflight.LoadOrStore(cfg.Name, &sync.WaitGroup{})
// We used to call Add(1) in the "else" clause of the "if loaded"
// statement. This caused a data race because it was possible
// that one go routine stores (with count==0) and another routine
// gets "loaded==true" and calls wg.Wait() while the other routine
// then calls wg.Add(1). It also could mean that two routines execute
// the rest of the code concurrently.
swg := &sync.WaitGroup{}
swg.Add(1)
v, loaded := jsa.inflight.LoadOrStore(cfg.Name, swg)
wg := v.(*sync.WaitGroup)
if loaded {
wg.Wait()
// This waitgroup is "thrown away" (since there was an existing one).
swg.Done()
} else {
wg.Add(1)
defer func() {
jsa.inflight.Delete(cfg.Name)
wg.Done()
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