Return a Function on successful UnitOfWork.commit() so as to allow users to execute code post-commit iff that commit was successful.

src/main/java/net/helenus/core/HelenusSession.java

@@ -151,11 +151,15 @@ public final class HelenusSession extends AbstractSessionOperations implements C
 		}
 	}
 
-	public synchronized void commit() throws ConflictingUnitOfWorkException {
-        if (currentUnitOfWork != null) {
-            currentUnitOfWork.commit();
-            currentUnitOfWork = null;
+    public synchronized Function<Void, Void> commit() throws ConflictingUnitOfWorkException {
+        final Function<Void, Void> f = Function.<Void>identity();
+	    synchronized(currentUnitOfWork) {
+            if (currentUnitOfWork != null) {
+                currentUnitOfWork.commit().andThen((it) -> { return f; });
+                currentUnitOfWork = null;
+            }
         }
+        return f;
 	}
 
 	public synchronized void abort() {

src/main/java/net/helenus/core/UnitOfWork.java

@@ -1,6 +1,7 @@
 package net.helenus.core;
 
 import java.util.ArrayList;
+import java.util.function.Function;
 
 /**
  * Encapsulates the concept of a "transaction" as a unit-of-work.
@@ -34,15 +35,17 @@ public class UnitOfWork {
 	 * Checks to see if the work performed between calling begin and now can be
 	 * committed or not.
 	 *
+     * @return a function from which to chain work that only happens when commit is successful
 	 * @throws ConflictingUnitOfWorkException
 	 *             when the work overlaps with other concurrent writers.
 	 */
-	public void commit() throws ConflictingUnitOfWorkException {
+	public Function<Void, Void> commit() throws ConflictingUnitOfWorkException {
 		// nested.foreach.commit()
 		// log.record(txn::provisionalCommit)
 		// examine log for conflicts in read-set and write-set between begin and
 		// provisional commit
 		// if (conflict) { throw new ConflictingUnitOfWorkException(this) }
+		return Function.<Void>identity();
 	}
 
 	/**