1 files changed, 112 insertions, 0 deletions
diff --git a/src/mongo/db/pipeline/document_source_limit.cpp b/src/mongo/db/pipeline/document_source_limit.cpp
new file mode 100644
index 00000000000..8bbcaff2113
--- /dev/null
+++ b/src/mongo/db/pipeline/document_source_limit.cpp
@@ -0,0 +1,112 @@
+/**
+*    Copyright (C) 2011 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 "pch.h"
+
+#include "db/pipeline/document_source.h"
+
+#include "db/jsobj.h"
+#include "db/pipeline/document.h"
+#include "db/pipeline/expression.h"
+#include "db/pipeline/expression_context.h"
+#include "db/pipeline/value.h"
+
+namespace mongo {
+    const char DocumentSourceLimit::limitName[] = "$limit";
+
+    DocumentSourceLimit::DocumentSourceLimit(
+        const intrusive_ptr<ExpressionContext> &pExpCtx):
+        DocumentSource(pExpCtx),
+        limit(0),
+        count(0) {
+    }
+
+    DocumentSourceLimit::~DocumentSourceLimit() {
+    }
+
+    const char *DocumentSourceLimit::getSourceName() const {
+        return limitName;
+    }
+
+    bool DocumentSourceLimit::coalesce(
+        const intrusive_ptr<DocumentSource> &pNextSource) {
+        DocumentSourceLimit *pLimit =
+            dynamic_cast<DocumentSourceLimit *>(pNextSource.get());
+
+        /* if it's not another $skip, we can't coalesce */
+        if (!pLimit)
+            return false;
+
+        /* we need to limit by the minimum of the two limits */
+        if (pLimit->limit < limit)
+            limit = pLimit->limit;
+        return true;
+    }
+
+    bool DocumentSourceLimit::eof() {
+        return pSource->eof() || count >= limit;
+    }
+
+    bool DocumentSourceLimit::advance() {
+        DocumentSource::advance(); // check for interrupts
+
+        ++count;
+        if (count >= limit) {
+
+            pCurrent.reset();
+
+            // This is requried for the DocumentSourceCursor to release its read lock, see
+            // SERVER-6123.
+            pSource->dispose();
+
+            return false;
+        }
+        pCurrent = pSource->getCurrent();
+        return pSource->advance();
+    }
+
+    intrusive_ptr<Document> DocumentSourceLimit::getCurrent() {
+        return pSource->getCurrent();
+    }
+
+    void DocumentSourceLimit::sourceToBson(
+        BSONObjBuilder *pBuilder, bool explain) const {
+        pBuilder->append("$limit", limit);
+    }
+
+    intrusive_ptr<DocumentSourceLimit> DocumentSourceLimit::create(
+        const intrusive_ptr<ExpressionContext> &pExpCtx) {
+        intrusive_ptr<DocumentSourceLimit> pSource(
+            new DocumentSourceLimit(pExpCtx));
+        return pSource;
+    }
+
+    intrusive_ptr<DocumentSource> DocumentSourceLimit::createFromBson(
+        BSONElement *pBsonElement,
+        const intrusive_ptr<ExpressionContext> &pExpCtx) {
+        uassert(15957, "the limit must be specified as a number",
+                pBsonElement->isNumber());
+
+        intrusive_ptr<DocumentSourceLimit> pLimit(
+            DocumentSourceLimit::create(pExpCtx));
+
+        pLimit->limit = (int)pBsonElement->numberLong();
+        uassert(15958, "the limit must be positive",
+                pLimit->limit > 0);
+
+        return pLimit;
+    }
+}