SERVER-47350 Add execution context as a decoration to OperationContext

It is meant to be a container for reusing temporary objects within an operation instead of creating and destroying new instances.

At the moment, used for index building where it keeps data structures for KeyStringSet and MultikeyPaths.

1 files changed, 58 insertions, 0 deletions

diff --git a/src/mongo/util/auto_clear_ptr.h b/src/mongo/util/auto_clear_ptr.h
new file mode 100644
index 00000000000..7ea2b8254c8
--- /dev/null
+++ b/src/mongo/util/auto_clear_ptr.h
@@ -0,0 +1,58 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    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 Server Side 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.
+ */
+
+#pragma once
+
+#include <memory>
+
+namespace mongo {
+
+template <class Container>
+class ClearDeleter {
+public:
+    void operator()(Container* container) {
+        container->clear();
+    }
+};
+
+/**
+ * A RAII style move-only pointer that calls clear() when going out of scope
+ */
+template <class Container>
+using AutoClearPtr = std::unique_ptr<Container, ClearDeleter<Container>>;
+
+template <class Container>
+auto makeAutoClearPtr(Container* container) {
+    // It should always be cleared when it is accessed
+    dassert(container);
+    dassert(container->empty());
+    return AutoClearPtr<Container>{container, ClearDeleter<Container>{}};
+}
+
+}  // namespace mongo