bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/lazy/Lazy.java

   1 package org.simantics.scl.runtime.lazy;
   2
   3 import org.simantics.scl.runtime.function.Function;
   4 import org.simantics.scl.runtime.function.FunctionImpl1;
   5 import org.simantics.scl.runtime.tuple.Tuple0;
   6
   7 public class Lazy {
   8     private static final Function CYCLIC_EVALUATION_TRAP = new FunctionImpl1() {
   9         @Override
  10         public Object apply(Object p0) {
  11             throw new RuntimeException("Cyclic dependency on lazy value.");
  12         }
  13     };
  14
  15     volatile Function thunk;
  16     volatile Object value;
  17
  18     public Lazy(Function thunk) {
  19         this.thunk = thunk;
  20     }
  21
  22     public Object force() {
  23         if(thunk == null)
  24             return value;
  25         else {
  26             synchronized(this) {
  27                 Function curThunk = thunk;
  28                 if(curThunk != null) {
  29                     thunk = CYCLIC_EVALUATION_TRAP;
  30                     value = curThunk.apply(Tuple0.INSTANCE);
  31                     thunk = null;
  32                 }
  33             }
  34             return value;
  35         }
  36     }
  37 }