// blockUntilNextLog returns a channel that will have data sent when the next
// log index or anything greater is created.
func blockUntilNextLog(fs allocdir.AllocDirFS, t *tomb.Tomb, logPath, task, logType string, nextIndex int64) chan error {
nextPath := filepath.Join(logPath, fmt.Sprintf("%s.%s.%d", task, logType, nextIndex))
next := make(chan error, 1)
go func() {
eofCancelCh, err := fs.BlockUntilExists(nextPath, t)
if err != nil {
next <- err
close(next)
return
}
ticker := time.NewTicker(nextLogCheckRate)
defer ticker.Stop()
scanCh := ticker.C
for {
select {
case <-t.Dead():
next <- fmt.Errorf("shutdown triggered")
close(next)
return
case err := <-eofCancelCh:
next <- err
close(next)
return
case <-scanCh:
entries, err := fs.List(logPath)
if err != nil {
next <- fmt.Errorf("failed to list entries: %v", err)
close(next)
return
}
indexes, err := logIndexes(entries, task, logType)
if err != nil {
next <- err
close(next)
return
}
// Scan and see if there are any entries larger than what we are
// waiting for.
for _, entry := range indexes {
if entry.idx >= nextIndex {
next <- nil
close(next)
return
}
}
}
}
}()
return next
}
