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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/>.
*/
#pragma once
#include "mongo/db/query/canonical_query.h"
namespace mongo {
/**
* A runner runs a query.
*/
class Runner {
public:
virtual ~Runner() { }
enum RunnerState {
// We successfully populated the out parameter.
RUNNER_ADVANCED,
// We're EOF. We won't return any more results (edge case exception: capped+tailable).
RUNNER_EOF,
// We were killed or had an error.
RUNNER_DEAD,
};
/**
* Get the next result from the query.
*/
virtual RunnerState getNext(BSONObj* objOut) = 0;
/**
* Inform the runner that the provided DiskLoc is about to disappear (or change entirely).
* The runner then takes any actions required to continue operating correctly, including
* broadcasting the invalidation request to the PlanStage tree being run.
*
* Called from ClientCursor::aboutToDelete.
*/
virtual void invalidate(const DiskLoc& dl) = 0;
/**
* Save any state required to yield.
*/
virtual void saveState() = 0;
/**
* Restore saved state, possibly after a yield.
*/
virtual void restoreState() = 0;
/**
* Return the query that the runner is running.
*/
virtual const CanonicalQuery& getQuery() = 0;
/**
* Mark the Runner as no longer valid. Can happen when a runner yields and the underlying
* database is dropped/indexes removed/etc. All future to calls to getNext return
* RUNNER_DEAD. Every other call is a NOOP.
*/
virtual void kill() = 0;
/**
* Force the runner to yield. Gives up any locks it had before. Holds locks again when the
* runner returns from the yield. Returns true if it's OK to continue using the runner,
* false if the runner was killed during a yield.
*/
virtual bool forceYield() = 0;
};
} // namespace mongo
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