/// <summary>
/// Maintenance task to ensure that the local node has valid successor node. Roughly equivalent
/// to what is called out in the Chord paper.
/// </summary>
/// <param name="sender">The worker thread the task is running on.</param>
/// <param name="ea">Args (ignored here).</param>
private void StabilizeSuccessors(object sender, DoWorkEventArgs ea)
{
BackgroundWorker me = (BackgroundWorker)sender;
while (!me.CancellationPending)
{
try
{
// check in successor and if it's bad, replace it with
// the next live entry in the successor cache
ChordNode succPredNode = ChordServer.GetPredecessor(this.Successor);
if (succPredNode != null)
{
if (ChordServer.IsIDInRange(succPredNode.ID, this.ID, this.Successor.ID))
{
this.Successor = succPredNode;
}
// ignoring return because bad node will be detected on next invocation
ChordServer.CallNotify(this.Successor, ChordServer.LocalNode);
GetSuccessorCache(this.Successor);
}
else
{
bool successorCacheHelped = false;
foreach (ChordNode entry in this.m_SuccessorCache)
{
ChordInstance instance = ChordServer.GetInstance(entry);
if (ChordServer.IsInstanceValid(instance))
{
this.Successor = entry;
ChordServer.CallNotify(this.Successor, ChordServer.LocalNode);
GetSuccessorCache(this.Successor);
successorCacheHelped = true;
break;
}
}
// if we get here, then we got no help and have no other recourse than to re-join using the initial seed...
if (!successorCacheHelped)
{
ChordServer.Log(LogLevel.Error, "StabilizeSuccessors", "Ring consistency error, Re-Joining Chord ring.");
Join(this.m_SeedNode, this.Host, this.Port);
return;
}
}
}
catch (Exception e)
{
ChordServer.Log(LogLevel.Error, "Maintenance", "Error occured during StabilizeSuccessors ({0})", e.Message);
}
// TODO: this could be tweaked and/or made configurable elsewhere or passed in as arguments
Thread.Sleep(5000);
}
}
