func (m *MemDB) NewSnapshot() (*Snapshot, error) {
buf := m.snapshots.MakeBuf()
defer m.snapshots.FreeBuf(buf)
// Stitch all local gclists from all writers to create snapshot gclist
var head, tail *skiplist.Node
for w := m.wlist; w != nil; w = w.next {
if tail == nil {
head = w.gchead
tail = w.gctail
} else if w.gchead != nil {
tail.GClink = w.gchead
tail = w.gctail
}
w.gchead = nil
w.gctail = nil
// Update global stats
m.store.Stats.Merge(&w.slSts1)
atomic.AddInt64(&m.itemsCount, w.count)
w.count = 0
}
snap := &Snapshot{db: m, sn: m.getCurrSn(), refCount: 1, count: m.ItemsCount()}
m.snapshots.Insert(unsafe.Pointer(snap), CompareSnapshot, buf, &m.snapshots.Stats)
snap.gclist = head
newSn := atomic.AddUint32(&m.currSn, 1)
if newSn == math.MaxUint32 {
return nil, ErrMaxSnapshotsLimitReached
}
return snap, nil
}
func (w *Writer) DeleteNode(x *skiplist.Node) (success bool) {
defer func() {
if success {
w.count -= 1
}
}()
x.GClink = nil
sn := w.getCurrSn()
gotItem := (*Item)(x.Item())
if gotItem.bornSn == sn {
success = w.store.DeleteNode(x, w.insCmp, w.buf, &w.slSts1)
barrier := w.store.GetAccesBarrier()
barrier.FlushSession(unsafe.Pointer(x))
return
}
success = atomic.CompareAndSwapUint32(&gotItem.deadSn, 0, sn)
if success {
if w.gctail == nil {
w.gctail = x
w.gchead = w.gctail
} else {
w.gctail.GClink = x
w.gctail = x
}
}
return
}