From: Brian Norris <banorris@uci.edu>
Date: Fri, 1 Feb 2013 23:11:13 +0000 (-0800)
Subject: cyclegraph: add full promise resolution, node merging
X-Git-Tag: oopsla2013~302
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=model-checker.git;a=commitdiff_plain;h=d3dffe991352938e5c2ab738ce70e3ec0f069d5f

cyclegraph: add full promise resolution, node merging

We now support the interfaces needed for tracking Promise constraints in
CycleGraph.
---

diff --git a/cyclegraph.cc b/cyclegraph.cc
index 479ddf8..46b0d4a 100644
--- a/cyclegraph.cc
+++ b/cyclegraph.cc
@@ -90,6 +90,89 @@ void CycleGraph::addEdge(const T from, const U to)
 	addNodeEdge(fromnode, tonode);
 }
 
+/**
+ * @return false if the resolution results in a cycle; true otherwise
+ */
+bool CycleGraph::resolvePromise(ModelAction *reader, ModelAction *writer,
+		promise_list_t *mustResolve)
+{
+	CycleNode *promise_node = readerToPromiseNode.get(reader);
+	CycleNode *w_node = actionToNode.get(writer);
+	ASSERT(promise_node);
+
+	if (w_node)
+		return mergeNodes(w_node, promise_node, mustResolve);
+	/* No existing write-node; just convert the promise-node */
+	promise_node->resolvePromise(writer);
+	readerToPromiseNode.put(reader, NULL); /* erase promise_node */
+	putNode(writer, promise_node);
+	return true;
+}
+
+/**
+ * @brief Merge two CycleNodes that represent the same write
+ *
+ * Note that this operation cannot be rolled back.
+ *
+ * @param w_node The write ModelAction node with which to merge
+ * @param p_node The Promise node to merge. Will be destroyed after this
+ * function.
+ * @param mustMerge Return (pass-by-reference) any additional Promises that
+ * must also be merged with w_node
+ *
+ * @return false if the merge results in a cycle; true otherwise
+ */
+bool CycleGraph::mergeNodes(CycleNode *w_node, CycleNode *p_node,
+		promise_list_t *mustMerge)
+{
+	ASSERT(!w_node->is_promise());
+	ASSERT(p_node->is_promise());
+	const Promise *promise = p_node->getPromise();
+	if (!promise->is_compatible(w_node->getAction())) {
+		hasCycles = true;
+		return false;
+	}
+
+	/* Transfer back edges to w_node */
+	while (p_node->getNumBackEdges() > 0) {
+		CycleNode *back = p_node->removeBackEdge();
+		if (back != w_node) {
+			if (back->is_promise()) {
+				if (checkReachable(w_node, back)) {
+					/* Edge would create cycle; merge instead */
+					mustMerge->push_back(back->getPromise());
+					if (!mergeNodes(w_node, back, mustMerge))
+						return false;
+				} else
+					back->addEdge(w_node);
+			} else
+				addNodeEdge(back, w_node);
+		}
+	}
+
+	/* Transfer forward edges to w_node */
+	while (p_node->getNumEdges() > 0) {
+		CycleNode *forward = p_node->removeEdge();
+		if (forward != w_node) {
+			if (forward->is_promise()) {
+				if (checkReachable(forward, w_node)) {
+					mustMerge->push_back(forward->getPromise());
+					if (!mergeNodes(w_node, forward, mustMerge))
+						return false;
+				} else
+					w_node->addEdge(forward);
+			} else
+				addNodeEdge(w_node, forward);
+		}
+	}
+
+	/* erase p_node */
+	readerToPromiseNode.put(promise->get_action(), NULL);
+	delete p_node;
+
+	return !hasCycles;
+}
+
 /**
  * Adds an edge between two CycleNodes.
  * @param fromnode The edge comes from this CycleNode
diff --git a/cyclegraph.h b/cyclegraph.h
index e7e9380..c0bd7d6 100644
--- a/cyclegraph.h
+++ b/cyclegraph.h
@@ -19,6 +19,8 @@ class Promise;
 class CycleNode;
 class ModelAction;
 
+typedef std::vector< const Promise *, ModelAlloc<const Promise *> > promise_list_t;
+
 /** @brief A graph of Model Actions for tracking cycles. */
 class CycleGraph {
  public:
@@ -40,12 +42,17 @@ class CycleGraph {
 	void dumpGraphToFile(const char *filename) const;
 #endif
 
+	bool resolvePromise(ModelAction *reader, ModelAction *writer,
+			promise_list_t *mustResolve);
+
 	SNAPSHOTALLOC
  private:
 	void addNodeEdge(CycleNode *fromnode, CycleNode *tonode);
 	void putNode(const ModelAction *act, CycleNode *node);
 	CycleNode * getNode(const ModelAction *);
 	CycleNode * getNode(const Promise *promise);
+	bool mergeNodes(CycleNode *node1, CycleNode *node2,
+			promise_list_t *mustMerge);
 
 	HashTable<const CycleNode *, const CycleNode *, uintptr_t, 4, model_malloc, model_calloc, model_free> *discovered;