/// <summary>
/// Transfers the data with the key and entry to the local store.
/// </summary>
/// <param name="entry"></param>
/// <param name="value"></param>
/// <param name="dht"></param>
/// <param name="cancellationToken"></param>
/// <returns></returns>
async Task TransferAsync(IKsStoreEntry <TKey> entry, KsHashTableValue value, KsHashTableEntry dht, CancellationToken cancellationToken)
{
foreach (var uri in dht.Endpoints)
{
// we can't pull the value from ourselves, move to secondaries
if (uri == options.Value.Uri)
{
continue;
}
var client = clients.Get(uri);
if (client == null)
{
throw new KsException($"Could not obtain client for remote host: '{uri}'");
}
// existing token if we're resuming an operation after failure
var t = await entry.GetOwnerTokenAsync(cancellationToken);
var v = await client.ShiftLockAsync(entry.Key, t, cancellationToken);
// current owner returns no value, must not really own it, nothing to transfer
if (v == null)
{
return;
}
// track down owner by following forwards
while (v.Value.ForwardUri != null)
{
client = clients.Get(v.Value.ForwardUri);
v = await client.ShiftLockAsync(entry.Key, t, cancellationToken);
}
if (v.Value.Data == null)
{
throw new KsException("Data not retrieved.");
}
if (v.Value.Data == null)
{
throw new KsException("Data retrieved, but not token.");
}
// update local entry with latest information
await entry.SetOwnerTokenAsync(t = v.Value.Token);
await entry.SetAsync(v.Value.Data);
// finalize shift on remote node and publish entry
await client.ShiftAsync(entry.Key, t, options.Value.Uri, cancellationToken);
await hashtable.AddAsync(entry.Key, new KsHashTableValue(Serialize(new KsHashTableEntry(new[] { options.Value.Uri })), value.Version + 1, TimeSpan.FromDays(1)));
// we succeeded, exit loop
break;
}
// zero out lock token if we successfully complete process
await entry.SetOwnerTokenAsync(null);
}
/// <summary>
/// Executes the given function after ensuring ownership of the key.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="key"></param>
/// <param name="func"></param>
/// <param name="cancellationToken"></param>
/// <returns></returns>
async Task <T> Access <T>(TKey key, Func <IKsStoreEntry <TKey>, CancellationToken, Task <T> > func, bool shift, CancellationToken cancellationToken)
{
await using var entry = await store.OpenAsync(key, cancellationToken);
var v = await hashtable.GetAsync(key, cancellationToken);
// value is unknown to the system
if (v == null)
{
// initial publish of DHT record
v = new KsHashTableValue(Serialize(new KsHashTableEntry(new[] { options.Value.Uri })), 1, TimeSpan.FromDays(1));
await hashtable.AddAsync(key, v, cancellationToken);
return(await func(entry, cancellationToken));
}
// try to transfer object until transfer succeeds
if (shift)
{
var e = Deserialize(v.Value.Data);
while (e.Endpoints.Length == 0 || e.Endpoints[0] != options.Value.Uri)
{
await TransferAsync(entry, v.Value, e, cancellationToken);
v = await hashtable.GetAsync(key, cancellationToken);
e = Deserialize(v.Value.Data);
}
}
return(await func(entry, cancellationToken));
}
