/// <summary>Chooses datanode locations for caching from a list of valid possibilities.
/// </summary>
/// <remarks>
/// Chooses datanode locations for caching from a list of valid possibilities.
/// Non-stale nodes are chosen before stale nodes.
/// </remarks>
/// <param name="possibilities">List of candidate datanodes</param>
/// <param name="neededCached">Number of replicas needed</param>
/// <param name="staleInterval">Age of a stale datanode</param>
/// <returns>A list of chosen datanodes</returns>
private static IList <DatanodeDescriptor> ChooseDatanodesForCaching(IList <DatanodeDescriptor
> possibilities, int neededCached, long staleInterval)
{
// Make a copy that we can modify
IList <DatanodeDescriptor> targets = new AList <DatanodeDescriptor>(possibilities);
// Selected targets
IList <DatanodeDescriptor> chosen = new List <DatanodeDescriptor>();
// Filter out stale datanodes
IList <DatanodeDescriptor> stale = new List <DatanodeDescriptor>();
IEnumerator <DatanodeDescriptor> it = targets.GetEnumerator();
while (it.HasNext())
{
DatanodeDescriptor d = it.Next();
if (d.IsStale(staleInterval))
{
it.Remove();
stale.AddItem(d);
}
}
// Select targets
while (chosen.Count < neededCached)
{
// Try to use stale nodes if we're out of non-stale nodes, else we're done
if (targets.IsEmpty())
{
if (!stale.IsEmpty())
{
targets = stale;
}
else
{
break;
}
}
// Select a random target
DatanodeDescriptor target = ChooseRandomDatanodeByRemainingCapacity(targets);
chosen.AddItem(target);
targets.Remove(target);
}
return(chosen);
}