nodestack: add release sequence breakage backtracking

End-of-execution resolution of release sequences requires a search
procedure in which we test various attempts at breaking our pending
release sequences. This provides the NodeStack infrastructure.

diff --git a/nodestack.cc b/nodestack.cc
index 4cf89500fc1faba0f98714173fbd4eca557edefa..72c8d5cf5e46f7dca4241aa12f26958439ad15c3 100644 (file)
--- a/nodestack.cc
+++ b/nodestack.cc
@@ -32,7 +32,9 @@ Node::Node(ModelAction *act, Node *par, int nthreads, Node *prevfairness)
        may_read_from(),
        read_from_index(0),
        future_values(),
-       future_index(-1)
+       future_index(-1),
+       relseq_break_writes(),
+       relseq_break_index(0)
 {
        if (act) {
                act->set_node(this);
@@ -352,6 +354,58 @@ bool Node::increment_future_value() {
        return false;
 }
 
+/**
+ * Add a write ModelAction to the set of writes that may break the release
+ * sequence. This is used during replay exploration of pending release
+ * sequences. This Node must correspond to a release sequence fixup action.
+ *
+ * @param write The write that may break the release sequence. NULL means we
+ * allow the release sequence to synchronize.
+ */
+void Node::add_relseq_break(const ModelAction *write)
+{
+       relseq_break_writes.push_back(write);
+}
+
+/**
+ * Get the write that may break the current pending release sequence,
+ * according to the replay / divergence pattern.
+ *
+ * @return A write that may break the release sequence. If NULL, that means
+ * the release sequence should not be broken.
+ */
+const ModelAction * Node::get_relseq_break()
+{
+       if (relseq_break_index < (int)relseq_break_writes.size())
+               return relseq_break_writes[relseq_break_index];
+       else
+               return NULL;
+}
+
+/**
+ * Increments the index into the relseq_break_writes set to explore the next
+ * item.
+ * @return Returns false if we have explored all values.
+ */
+bool Node::increment_relseq_break()
+{
+       DBG();
+       promises.clear();
+       if (relseq_break_index < ((int)relseq_break_writes.size())) {
+               relseq_break_index++;
+               return (relseq_break_index < ((int)relseq_break_writes.size()));
+       }
+       return false;
+}
+
+/**
+ * @return True if all writes that may break the release sequence have been
+ * explored
+ */
+bool Node::relseq_break_empty() {
+       return ((relseq_break_index + 1) >= ((int)relseq_break_writes.size()));
+}
+
 void Node::explore(thread_id_t tid)
 {
        int i = id_to_int(tid);

diff --git a/nodestack.h b/nodestack.h
index 55deac5beffa2a6a0d3deec210c4246f0b8074db..cb281cad65b1dbf7f60892f9c656ce0061afee84 100644 (file)
--- a/nodestack.h
+++ b/nodestack.h
@@ -91,6 +91,11 @@ public:
        bool increment_promise();
        bool promise_empty();
 
+       void add_relseq_break(const ModelAction *write);
+       const ModelAction * get_relseq_break();
+       bool increment_relseq_break();
+       bool relseq_break_empty();
+
        void print();
        void print_may_read_from();
 
@@ -116,6 +121,9 @@ private:
        std::vector< struct future_value, ModelAlloc<struct future_value> > future_values;
        std::vector< promise_t, ModelAlloc<promise_t> > promises;
        int future_index;
+
+       std::vector< const ModelAction *, ModelAlloc<const ModelAction *> > relseq_break_writes;
+       int relseq_break_index;
 };
 
 typedef std::vector< Node *, ModelAlloc< Node * > > node_list_t;