func (q *Queue) Dequeue(startId ...uint64) (uint64, []byte, error) {
store := q.store
var seekId uint64 = 1
if len(startId) > 0 {
seekId = startId[0]
}
if seekId < 1 {
seekId = 1
}
var it *rocks.Iterator
if q.useTailing {
it = q.tailIterator
if !it.Valid() {
// FIXME?(mijia): When Dequeue happens faster than enqueue, the tail iterator would be exhausted
// so we have seek it again.
it.Seek(q.key(seekId))
}
} else {
it = store.NewIteratorCF(store.ro, q.cfHandle)
defer it.Close()
it.Seek(q.key(seekId))
}
if !it.Valid() {
return 0, nil, EmptyQueue
}
wb := rocks.NewWriteBatch()
defer wb.Destroy()
key := makeSlice(it.Key())
value := makeSlice(it.Value())
wb.DeleteCF(q.cfHandle, key)
wb.MergeCF(q.cfHandle, q.metaKey("head"), oneBinary)
err := store.Write(store.wo, wb)
if err == nil {
atomic.AddUint64(&q.head, 1)
if q.useTailing {
it.Next()
}
}
id := q.id(key)
log.Debugf("[Queue] Dequeued data id=%d, err=%v", id, err)
return id, value, err
}
