internal override void Visit(ReadVersionRequest req)
{
VersionEntry versionEntry = req.RemoteVerEntry;
if (versionEntry == null)
{
ConcurrentDictionary <long, VersionEntry> versionList = null;
if (!this.dict.TryGetValue(req.RecordKey, out versionList))
{
req.Result = null;
req.Finished = true;
return;
}
if (!versionList.TryGetValue(req.VersionKey, out versionEntry))
{
req.Result = null;
req.Finished = true;
return;
}
}
Debug.Assert(Interlocked.Read(ref versionEntry.VersionKey) == req.VersionKey);
// Debug Assertion
// if (!versionEntry.RecordKey.Equals(req.RecordKey))
// {
// throw new Exception("Inconsistent record key");
// }
//int ticket = versionEntry.EnterQueuedLatch();
versionEntry.ReadLock();
VersionEntry.CopyFromRemote(versionEntry, req.LocalVerEntry);
//versionEntry.ExitQueuedLatch(ticket);
versionEntry.UnReadLock();
req.Result = req.LocalVerEntry;
req.Finished = true;
}
internal override void Visit(GetVersionListRequest req)
{
ConcurrentDictionary <long, VersionEntry> versionList = null;
if (!this.dict.TryGetValue(req.RecordKey, out versionList))
{
req.RemoteVerList = null;
req.Result = 0;
req.Finished = true;
return;
}
int entryCount = 0;
// The value at -1 in the version list is a special entry,
// whose beginTimestamp points to the newest version.
VersionEntry tailEntry = null;
versionList.TryGetValue(SingletonDictionaryVersionTable.TAIL_KEY, out tailEntry);
long lastVersionKey = Interlocked.Read(ref tailEntry.BeginTimestamp);
TxList <VersionEntry> localList = req.LocalContainer;
TxList <VersionEntry> remoteList = req.RemoteContainer;
// Only returns top 2 newest versions. This is enough for serializability.
// For other isolation levels, more versions may need to be returned.
// When old versions may be truncated, it is desirable to maintain a head pointer as well,
// so as to increase the lower bound of version keys and reduce the number of iterations.
while (lastVersionKey >= 0 && entryCount < 2)
{
VersionEntry verEntry = null;
if (versionList.TryGetValue(lastVersionKey, out verEntry))
{
//int ticket = verEntry.EnterQueuedLatch();
verEntry.ReadLock();
// Debug Assertion
// if (!verEntry.RecordKey.Equals(req.RecordKey))
// {
// throw new Exception("Inconsistent record key");
// }
VersionEntry.CopyFromRemote(verEntry, localList[entryCount]);
//verEntry.ExitQueuedLatch(ticket);
verEntry.UnReadLock();
// Here only add a reference to the list, no need to take the latch
remoteList.Add(verEntry);
entryCount++;
if (Interlocked.Read(ref verEntry.TxId) == VersionEntry.EMPTY_TXID)
{
break;
}
}
lastVersionKey--;
}
req.RemoteVerList = versionList;
req.Result = entryCount;
req.Finished = true;
}
