private static List <List <Node <TValue, TMetadata> > > FindCycles <TValue, TMetadata>(List <Node <TValue, TMetadata> > unsortedItems)
where TValue : class
where TMetadata : IOrderable
{
for (int i = 0; (i < unsortedItems.Count); ++i)
{
var n = unsortedItems[i];
n.Index = -1;
n.LowIndex = -1;
n.ContainedInKnownCycle = false;
}
List <List <Node <TValue, TMetadata> > > cycles = new List <List <Node <TValue, TMetadata> > >();
Stack <Node <TValue, TMetadata> > stack = new Stack <Node <TValue, TMetadata> >(unsortedItems.Count);
int index = 0;
for (int i = 0; (i < unsortedItems.Count); ++i)
{
var node = unsortedItems[i];
if (node.Index == -1)
{
Orderer.FindCycles(node, stack, ref index, cycles);
Debug.Assert(stack.Count == 0);
}
}
return(cycles);
}
public static IList <Lazy <TValue, TMetadata> > Order <TValue, TMetadata>(IEnumerable <Lazy <TValue, TMetadata> > itemsToOrder)
where TValue : class
where TMetadata : IOrderable
{
if (itemsToOrder == null)
{
throw new ArgumentNullException(nameof(itemsToOrder));
}
#if false && DEBUG
Debug.WriteLine("Before ordering");
DumpGraph(itemsToOrder);
#endif
var roots = new Queue <Node <TValue, TMetadata> >();
var unsortedItems = new List <Node <TValue, TMetadata> >();
Orderer.PrepareGraph(itemsToOrder, roots, unsortedItems);
IList <Lazy <TValue, TMetadata> > sortedItems = Orderer.TopologicalSort(roots, unsortedItems);
#if false && DEBUG
Debug.WriteLine("After ordering");
DumpGraph(sortedItems);
#endif
return(sortedItems);
}
public void ClearBefore(Queue <Node <TValue, TMetadata> > roots)
{
List <Node <TValue, TMetadata> > newRoots = new List <Node <TValue, TMetadata> >();
foreach (Node <TValue, TMetadata> child in this.Before)
{
child.After.Remove(this);
if (child.After.Count == 0)
{
newRoots.Add(child);
}
}
this.Before.Clear();
Orderer.AddToRoots(roots, newRoots);
}
private static void FindCycles <TValue, TMetadata>(Node <TValue, TMetadata> node, Stack <Node <TValue, TMetadata> > stack, ref int index, List <List <Node <TValue, TMetadata> > > cycles)
where TValue : class
where TMetadata : IOrderable
{
node.Index = index;
node.LowIndex = index;
++index;
stack.Push(node);
foreach (Node <TValue, TMetadata> child in node.Before)
{
if (child.Index == -1)
{
Orderer.FindCycles(child, stack, ref index, cycles);
node.LowIndex = Math.Min(node.LowIndex, child.LowIndex);
}
else if (!child.ContainedInKnownCycle)
{
node.LowIndex = Math.Min(node.LowIndex, child.Index);
}
}
if (node.Index == node.LowIndex)
{
List <Node <TValue, TMetadata> > cycle = new List <Node <TValue, TMetadata> >();
while (stack.Count > 0)
{
Node <TValue, TMetadata> child = stack.Pop();
cycle.Add(child);
child.ContainedInKnownCycle = true;
if (child == node)
{
//Single unit cycles aren't interesting (since we are preventing node from linking to themselves in the Resolve code below).
if (cycle.Count > 1)
{
cycles.Add(cycle);
}
break;
}
Debug.Assert(stack.Count > 0);
}
}
}
private static IList <Lazy <TValue, TMetadata> > TopologicalSort <TValue, TMetadata>(Queue <Node <TValue, TMetadata> > roots, List <Node <TValue, TMetadata> > unsortedItems)
where TValue : class
where TMetadata : IOrderable
{
List <Lazy <TValue, TMetadata> > sortedItems = new List <Lazy <TValue, TMetadata> >();
while (unsortedItems.Count > 0)
{
Node <TValue, TMetadata> node = (roots.Count == 0) ? Orderer.BreakCircularReference(unsortedItems) : roots.Dequeue();
Debug.Assert(node.After.Count == 0);
if (node.Item != null)
{
sortedItems.Add(node.Item);
}
unsortedItems.Remove(node);
node.ClearBefore(roots);
}
return(sortedItems);
}
private static Node <TValue, TMetadata> BreakCircularReference <TValue, TMetadata>(List <Node <TValue, TMetadata> > unsortedItems)
where TValue : class
where TMetadata : IOrderable
{
//We have a circular reference in the unsortedItems.
//This is an error in the definition that we need to handle gracefully.
//Find & report the cycle.
List <List <Node <TValue, TMetadata> > > cycles = Orderer.FindCycles(unsortedItems);
Debug.Assert(cycles.Count > 0);
#if DEBUG
Debug.WriteLine("Orderer found cycles:");
foreach (List <Node <TValue, TMetadata> > cycle in cycles)
{
foreach (Node <TValue, TMetadata> node in cycle)
{
Debug.Write("\t" + node.Name);
}
Debug.WriteLine("");
}
#endif
//Find the cycle with the fewest inbound links from other cycles.
int bestInwardLinkCount = int.MaxValue;
List <Node <TValue, TMetadata> > bestCycle = null;
for (int i = 0; (i < cycles.Count); ++i)
{
var cycle = cycles[i];
int inwardLinkCount = 0;
for (int j = 0; (j < cycle.Count); ++j)
{
var node = cycle[j];
foreach (Node <TValue, TMetadata> child in node.After)
{
if (child.LowIndex != node.LowIndex)
{
++inwardLinkCount;
break;
}
}
}
if (inwardLinkCount < bestInwardLinkCount)
{
bestCycle = cycle;
bestInwardLinkCount = inwardLinkCount;
}
}
//Given the best cycle we can find, pick the node that would break the smallest number of "after" constraints.
Node <TValue, TMetadata> bestNode;
if (bestCycle == null)
{
//Odd, no cycles were found so we need to guess at random.
bestNode = unsortedItems[0];
Debug.Fail("Orderer was unable to find a cycle to break");
}
else
{
bestNode = bestCycle[0];
for (int i = 1; (i < bestCycle.Count); ++i)
{
Node <TValue, TMetadata> node = bestCycle[i];
if (node.After.Count < bestNode.After.Count)
{
bestNode = node;
}
}
}
foreach (Node <TValue, TMetadata> a in bestNode.After)
{
a.Before.Remove(bestNode);
}
bestNode.After.Clear();
return(bestNode);
}
