/**
* Given a set of SCC nodes make this the lead member of the SCC and reroute all incoming and
* outgoing links accordingly. This eager rewrite is based on the assumption that there are few
* cycles so it is better to rewrite once and keep the graph easy to traverse.
*/
public void makeLeadNodeFor(Set<GraphNode> members) {
// Accumulate all successors
Set<GraphNode> newSucc = new HashSet<>();
Set<GraphNode> newSuccClosed = new HashSet<>();
for (GraphNode n : members) {
newSucc.addAll(n.succ);
newSuccClosed.addAll(n.succClosed);
}
newSucc.removeAll(members);
newSuccClosed.removeAll(members);
succ = newSucc;
succClosed = newSuccClosed;
// Rewrite all direct successors to have us as predecessor
for (GraphNode n : succ) {
n.pred.removeAll(members);
n.pred.add(this);
}
// Find all predecessor nodes and relink link them to point to us
Set<GraphNode> done = new HashSet<>();
Set<GraphNode> newAliases = new HashSet<>();
for (GraphNode member : members) {
addSiblings(newAliases, member);
}
becomeLeaderOf(newAliases);
for (GraphNode n : members) {
if (n != this) {
pred.addAll(n.pred);
n.relocateAllRefTo(this, done);
n.becomeSubordinateOf(this);
}
}
pred.removeAll(members);
}
/** Visit each predecessor of this node applying the given visitor. Breadth first. */
private <Alpha, Beta> void doVisitPredecessors(
Visitor<Alpha, Beta> visitor, Alpha arg1, Beta arg2, Set<GraphNode> seen) {
if (seen.add(this)) {
Collection<GraphNode> allKill = null;
for (Iterator<GraphNode> i = pred.iterator(); i.hasNext(); ) {
GraphNode pred = i.next();
List<GraphNode> kill = visitor.visit(pred, this, arg1, arg2);
if (kill != null) {
if (allKill == null) allKill = new ArrayList<GraphNode>();
allKill.addAll(kill);
}
}
if (allKill != null) pred.removeAll(allKill);
for (Iterator<GraphNode> i = pred.iterator(); i.hasNext(); ) {
GraphNode pred = i.next();
pred.doVisitPredecessors(visitor, arg1, arg2, seen);
}
}
}
/** Visit each predecessor of this node applying the given visitor. */
public <Alpha, Beta> void visitPredecessors(Visitor<Alpha, Beta> visitor, Alpha arg1, Beta arg2) {
List<GraphNode> kill = visitor.visit(this, null, arg1, arg2);
if (kill != null) pred.removeAll(kill);
doVisitPredecessors(visitor, arg1, arg2, new HashSet<GraphNode>());
}