--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/gov/nasa/jpf/search/heuristic/Interleaving.java	Fri Jan 23 10:14:01 2015 -0800
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2014, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ * 
+ *        http://www.apache.org/licenses/LICENSE-2.0. 
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and 
+ * limitations under the License.
+ */
+package gov.nasa.jpf.search.heuristic;
+
+import gov.nasa.jpf.Config;
+import gov.nasa.jpf.vm.VM;
+import gov.nasa.jpf.vm.Path;
+
+
+/**
+ * Heuristic to maximize thread interleavings. It is particularly good at
+ * flushing out concurrency errors, since it schedules different threads 
+ * as much as possible.
+ * 
+ */
+public class Interleaving extends SimplePriorityHeuristic {
+    
+  int historyLimit;
+
+  public Interleaving (Config config, VM vm) {
+    super(config,vm);
+    
+    historyLimit = config.getInt("search.heuristic.thread_history_limit", -1);
+  }
+
+  /*
+   * heuristic based on how often, how long ago, and within how many
+   * live threads a certain thread did run
+   */
+  @Override
+  protected int computeHeuristicValue () {
+    int aliveThreads = vm.getThreadList().getMatchingCount(aliveThread);
+
+    Path path = vm.getPath();
+    int  pathSize = path.size();
+    
+    int tid = vm.getCurrentThread().getId();
+    int h_value = 0;
+
+    if (aliveThreads > 1) { // otherwise there's nothing to interleave
+      
+      for (int i= Math.max(0, pathSize - historyLimit); i<pathSize; i++) {
+        if (path.get(i).getThreadIndex() == tid) {
+          h_value += (pathSize - i) * aliveThreads;
+        }
+      }
+    }
+
+    return h_value;
+  }
+}