+ /**
+ * Every Node has a phase; StateNodes belong to the phase in
+ * which they were shifted, ResultNodes belong to the phase of
+ * their predecessors. All of the predecessors of a given node
+ * must belong to the same phase
+ */
+ public Node(GSS.Phase phase, GSS.Phase predecessorPhase) {
+ this.phase = phase;
+ this.predecessorPhase = predecessorPhase;
+ }
+
+ private final GSS.Phase phase;
+ private final GSS.Phase predecessorPhase;
+ public GSS.Phase phase() { return phase; }
+ public GSS.Phase predecessorPhase() { return predecessorPhase; }
+ protected boolean destroyed = false;
+ private int numNonDoomedSuccessors = 0;
+ public boolean hasSuccessors() { return successors.size() > 0; }
+ public boolean hasNonDoomedSuccessors() { return numNonDoomedSuccessors > 0; }
+
+ /** only to be invoked (or overridden as public) by the subclass */
+ protected void addPred(OtherNode pred) {
+ if (predecessors.contains(pred)) throw new Error("a predecessor was added twice");
+ if (pred.phase() != predecessorPhase()) throw new Error();
+ predecessors.add(pred);
+ pred.addSucc(this);
+ }
+ public void addSucc(OtherNode succ) {
+ if (successors.contains(succ)) throw new Error("a predecessor was added twice");
+ successors.add(succ);
+ numNonDoomedSuccessors += succ.isDoomedState() ? 0 : 1;
+ if (predecessors.size() > 1 && (((Object)this) instanceof ResultNode)) throw new Error();
+ }
+ public void removeSucc(OtherNode succ) {
+ if (!successors.contains(succ)) return;
+ successors.remove(succ);
+ numNonDoomedSuccessors -= succ.isDoomedState() ? 0 : 1;
+ check();
+ }
+
+ protected void destroy() {
+ destroyed = true;
+ while(predecessors.size() > 0)
+ for(OtherNode pred : predecessors) {
+ removePred(pred);
+ pred.removeSucc(this);
+ break;
+ }
+ predecessors = null;
+ while(successors.size() > 0)
+ for(OtherNode succ : successors) {
+ removeSucc(succ);
+ succ.removePred(this);
+ break;
+ }
+ successors = null;
+ }
+
+ public abstract boolean isDoomedState();
+ protected abstract void check();
+
+ public void removePred(OtherNode pred) {
+ if (!predecessors.contains(pred)) return;
+ predecessors.remove(pred);
+ check();
+ }
+