bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/chr/CHRPriority.java

   1 package org.simantics.scl.runtime.chr;
   2
   3 /**
   4  * This class implements a pairing heap of CHR priorities.
   5  */
   6 public abstract class CHRPriority implements Comparable<CHRPriority> {
   7
   8     public final int priority;
   9
  10     // Pairing heap
  11     private CHRPriority sibling;
  12     private CHRPriority child;
  13
  14     boolean inContext;
  15
  16     public CHRPriority(int priority) {
  17         this.priority = priority;
  18     }
  19
  20     /**
  21      * This method assume that a and b are roots and their sibling field
  22      * can be overridden.
  23      */
  24     public static CHRPriority merge(CHRPriority a, CHRPriority b) {
  25         if(a.priority <= b.priority) {
  26             a.sibling = null;
  27             b.sibling = a.child;
  28             a.child = b;
  29             return a;
  30         }
  31         else {
  32             a.sibling = b.child;
  33             b.sibling = null;
  34             b.child = a;
  35             return b;
  36         }
  37     }
  38
  39     protected void ensureInContext(CHRContext context) {
  40         if(!inContext) {
  41             CHRPriority topPriority = context.topPriority;
  42             if(topPriority == null)
  43                 context.topPriority = this;
  44             else
  45                 context.topPriority = merge(topPriority, this);
  46             inContext = true;
  47         }
  48     }
  49
  50     private CHRPriority mergeSiblings() {
  51         if(sibling == null)
  52             return this;
  53         CHRPriority nextSibling = sibling.sibling;
  54         CHRPriority merged = merge(this, sibling);
  55         if(nextSibling == null)
  56             return merged;
  57         else
  58             return merge(merged, nextSibling.mergeSiblings());
  59     }
  60
  61     public CHRPriority nextPriority() {
  62         if(child == null)
  63             return null;
  64         else {
  65             CHRPriority result = child.mergeSiblings();
  66             child = null;
  67             return result;
  68         }
  69     }
  70
  71     @Override
  72     public int compareTo(CHRPriority o) {
  73         return Double.compare(priority, o.priority);
  74     }
  75
  76     public abstract void activate(CHRContext context);
  77     //public abstract CHRRuntimeRuleset getParent();
  78 }