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/**
* 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 <boost/scoped_ptr.hpp>
#include "mongo/db/clientcursor.h"
namespace mongo {
/**
* A RangePreserver prevents the RangeDeleter from removing any new data ranges in a collection.
* Previously queued ranges may still be deleted but the documents in those ranges will be
* filtered by CollectionMetadata::belongsToMe.
*
* TODO(greg/hk): Currently, creating a ClientCursor is how we accomplish this. This should
* change.
*/
class RangePreserver {
public:
/**
* Sharding uses the set of active cursor IDs as the current state. We add a dummy
* ClientCursor, which creates an additional cursor ID. The cursor ID lasts as long as this
* object does. The ClientCursorPin guarantees that the underlying ClientCursor is not
* deleted until this object goes out of scope.
*/
RangePreserver(const Collection* collection) {
invariant( collection );
// Not a memory leak. Cached in a static structure by CC's ctor.
ClientCursor* cc = new ClientCursor(collection);
// Pin keeps the CC from being deleted while it's in scope. We delete it ourselves.
_pin.reset(new ClientCursorPin(collection, cc->cursorid()));
}
~RangePreserver() {
_pin->deleteUnderlying();
}
private:
boost::scoped_ptr<ClientCursorPin> _pin;
};
} // namespace mongo
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