1 files changed, 74 insertions, 0 deletions
diff --git a/src/mongo/db/exec/simple_plan_runner.h b/src/mongo/db/exec/simple_plan_runner.h
new file mode 100644
index 00000000000..490d9ba4996
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+++ b/src/mongo/db/exec/simple_plan_runner.h
@@ -0,0 +1,74 @@
+/**
+ *    Copyright (C) 2013 10gen Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "mongo/db/exec/plan_stage.h"
+#include "mongo/db/exec/working_set.h"
+#include "mongo/db/exec/working_set_common.h"
+
+namespace mongo {
+
+    /**
+     * A placeholder for a full-featured plan runner.  Calls work() on a plan until a result is
+     * produced.  Stops when the plan is EOF or if the plan errors.
+     *
+     * TODO: Yielding policy
+     * TODO: Graceful error handling
+     * TODO: Fetch
+     * TODO: Stats, diagnostics, instrumentation, etc.
+     */
+    class SimplePlanRunner {
+    public:
+        SimplePlanRunner() { }
+
+        WorkingSet* getWorkingSet() { return &_workingSet; }
+
+        /**
+         * Takes ownership of root.
+         */
+        void setRoot(PlanStage* root) {
+            verify(root);
+            _root.reset(root);
+        }
+
+        bool getNext(BSONObj* objOut) {
+            for (;;) {
+                WorkingSetID id;
+                PlanStage::StageState code = _root->work(&id);
+
+                if (PlanStage::ADVANCED == code) {
+                    WorkingSetMember* member = _workingSet.get(id);
+                    uassert(16912, "Couldn't fetch obj from query plan",
+                            WorkingSetCommon::fetch(member));
+                    *objOut = member->obj;
+                    _workingSet.free(id);
+                    return true;
+                }
+                else if (code == PlanStage::NEED_TIME) {
+                    // TODO: Occasionally yield.  For now, we run until we get another result.
+                }
+                else {
+                    // IS_EOF, ERROR, NEED_YIELD.  We just stop here.
+                    return false;
+                }
+            }
+        }
+
+    private:
+        WorkingSet _workingSet;
+        scoped_ptr<PlanStage> _root;
+    };
+
+}  // namespace mongo