1 files changed, 106 insertions, 0 deletions
diff --git a/src/mongo/db/exec/limit.cpp b/src/mongo/db/exec/limit.cpp
new file mode 100644
index 00000000000..e084781dbaf
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+++ b/src/mongo/db/exec/limit.cpp
@@ -0,0 +1,106 @@
+/**
+ *    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/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/exec/limit.h"
+#include "mongo/db/exec/working_set_common.h"
+#include "mongo/util/mongoutils/str.h"
+
+namespace mongo {
+
+    LimitStage::LimitStage(int limit, WorkingSet* ws, PlanStage* child)
+        : _ws(ws), _child(child), _numToReturn(limit) { }
+
+    LimitStage::~LimitStage() { }
+
+    bool LimitStage::isEOF() { return (0 == _numToReturn) || _child->isEOF(); }
+
+    PlanStage::StageState LimitStage::work(WorkingSetID* out) {
+        ++_commonStats.works;
+
+        if (0 == _numToReturn) {
+            // We've returned as many results as we're limited to.
+            return PlanStage::IS_EOF;
+        }
+
+        WorkingSetID id = WorkingSet::INVALID_ID;
+        StageState status = _child->work(&id);
+
+        if (PlanStage::ADVANCED == status) {
+            *out = id;
+            --_numToReturn;
+            ++_commonStats.advanced;
+            return PlanStage::ADVANCED;
+        }
+        else if (PlanStage::FAILURE == status) {
+            *out = id;
+            // If a stage fails, it may create a status WSM to indicate why it
+            // failed, in which case 'id' is valid.  If ID is invalid, we
+            // create our own error message.
+            if (WorkingSet::INVALID_ID == id) {
+                mongoutils::str::stream ss;
+                ss << "limit stage failed to read in results from child";
+                Status status(ErrorCodes::InternalError, ss);
+                *out = WorkingSetCommon::allocateStatusMember( _ws, status);
+            }
+            return status;
+        }
+        else {
+            if (PlanStage::NEED_FETCH == status) {
+                *out = id;
+                ++_commonStats.needFetch;
+            }
+            else if (PlanStage::NEED_TIME == status) {
+                ++_commonStats.needTime;
+            }
+            return status;
+        }
+    }
+
+    void LimitStage::prepareToYield() {
+        ++_commonStats.yields;
+        _child->prepareToYield();
+    }
+
+    void LimitStage::recoverFromYield() {
+        ++_commonStats.unyields;
+        _child->recoverFromYield();
+    }
+
+    void LimitStage::invalidate(const DiskLoc& dl, InvalidationType type) {
+        ++_commonStats.invalidates;
+        _child->invalidate(dl, type);
+    }
+
+    PlanStageStats* LimitStage::getStats() {
+        _commonStats.isEOF = isEOF();
+        auto_ptr<PlanStageStats> ret(new PlanStageStats(_commonStats, STAGE_LIMIT));
+        ret->children.push_back(_child->getStats());
+        return ret.release();
+    }
+
+}  // namespace mongo