X-Git-Url: https://gerrit.simantics.org/r/gitweb?a=blobdiff_plain;f=bundles%2Forg.simantics.scl.runtime%2Fsrc%2Forg%2Fsimantics%2Fscl%2Fruntime%2Flazy%2FLazy.java;fp=bundles%2Forg.simantics.scl.runtime%2Fsrc%2Forg%2Fsimantics%2Fscl%2Fruntime%2Flazy%2FLazy.java;h=0c53fc97ac8619065ed5f507d3c8e437794a1aa7;hb=969bd23cab98a79ca9101af33334000879fb60c5;hp=0000000000000000000000000000000000000000;hpb=866dba5cd5a3929bbeae85991796acb212338a08;p=simantics%2Fplatform.git

diff --git a/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/lazy/Lazy.java b/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/lazy/Lazy.java
new file mode 100644
index 000000000..0c53fc97a
--- /dev/null
+++ b/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/lazy/Lazy.java
@@ -0,0 +1,37 @@
+package org.simantics.scl.runtime.lazy;
+
+import org.simantics.scl.runtime.function.Function;
+import org.simantics.scl.runtime.function.FunctionImpl1;
+import org.simantics.scl.runtime.tuple.Tuple0;
+
+public class Lazy {
+    private static final Function CYCLIC_EVALUATION_TRAP = new FunctionImpl1() {
+        @Override
+        public Object apply(Object p0) {
+            throw new RuntimeException("Cyclic dependency on lazy value.");
+        }
+    };
+    
+    volatile Function thunk;
+    volatile Object value;
+    
+    public Lazy(Function thunk) {
+        this.thunk = thunk;
+    }
+
+    public Object force() {
+        if(thunk == null)
+            return value;
+        else {
+            synchronized(this) {
+                Function curThunk = thunk;
+                if(curThunk != null) {
+                    thunk = CYCLIC_EVALUATION_TRAP;
+                    value = curThunk.apply(Tuple0.INSTANCE);
+                    thunk = null;
+                }
+            }
+            return value;
+        }
+    }
+}