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/**
* Copyright (C) 2015 MongoDB 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.
*/
#pragma once
#include <boost/optional.hpp>
#include <memory>
#include "mongo/base/status_with.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* This is the lightweight mongoS analogue of the PlanStage abstraction used to execute queries on
* mongoD (see mongo/db/plan_stage.h).
*
* Each subclass is a query execution stage which executes on the merging node. In general, the
* execution plan on mongos could have a tree of execution stages, but currently each node has at
* most one child. The leaf stage of the pipeline receives query result documents merged from the
* shards. The pipeline may then transform the result set in various ways before being returned by
* the root stage.
*/
class RouterExecStage {
public:
RouterExecStage() = default;
RouterExecStage(std::unique_ptr<RouterExecStage> child) : _child(std::move(child)) {}
virtual ~RouterExecStage() = default;
/**
* Returns the next query result, or an error.
*
* If there are no more results, returns boost::none.
*/
virtual StatusWith<boost::optional<BSONObj>> next() = 0;
/**
* Must be called before destruction to abandon a not-yet-exhausted plan. May block waiting for
* responses from remote hosts.
*/
virtual void kill() = 0;
/**
* Returns whether or not all the remote cursors are exhausted.
*/
virtual bool remotesExhausted() = 0;
/**
* Sets the maxTimeMS value that the cursor should forward with any internally issued getMore
* requests.
*
* Returns a non-OK status if this cursor type does not support maxTimeMS on getMore (i.e. if
* the cursor is not tailable + awaitData).
*/
virtual Status setAwaitDataTimeout(Milliseconds awaitDataTimeout) = 0;
protected:
/**
* Returns an unowned pointer to the child stage, or nullptr if there is no child.
*/
RouterExecStage* getChildStage() {
return _child.get();
}
private:
std::unique_ptr<RouterExecStage> _child;
};
} // namespace mongo
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