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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.
*/
#pragma once
#include "mongo/base/status.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/invalidation_type.h"
namespace mongo {
class Collection;
class DiskLoc;
class TypeExplain;
struct PlanInfo;
/**
* 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,
// getNext was asked for data it cannot provide, or the underlying PlanStage had an
// unrecoverable error.
// If the underlying PlanStage has any information on the error, it will be available in
// the objOut parameter. Call WorkingSetCommon::toStatusString() to retrieve the error
// details from the output BSON object.
RUNNER_ERROR,
};
static string statestr(RunnerState s) {
if (RUNNER_ADVANCED == s) {
return "RUNNER_ADVANCED";
}
else if (RUNNER_EOF == s) {
return "RUNNER_EOF";
}
else if (RUNNER_DEAD == s) {
return "RUNNER_DEAD";
}
else {
verify(RUNNER_ERROR == s);
return "RUNNER_ERROR";
}
}
/**
* Get the next result from the query.
*
* If objOut is not NULL, only results that have a BSONObj are returned. The BSONObj may
* point to on-disk data (isOwned will be false) and must be copied by the caller before
* yielding.
*
* If dlOut is not NULL, only results that have a valid DiskLoc are returned.
*
* If both objOut and dlOut are not NULL, only results with both a valid BSONObj and DiskLoc
* will be returned. The BSONObj is the object located at the DiskLoc provided.
*
* If the underlying query machinery produces a result that does not have the data requested
* by the user, it will be silently dropped.
*
* If the caller is running a query, they probably only care about the object.
* If the caller is an internal client, they may only care about DiskLocs (index scan), or
* about object + DiskLocs (collection scan).
*
* Some notes on objOut and ownership:
*
* objOut may be an owned object in certain cases: invalidation of the underlying DiskLoc,
* the object is created from covered index key data, the object is projected or otherwise
* the result of a computation.
*
* objOut will also be owned when the underlying PlanStage has provided error details in the
* event of a RUNNER_ERROR. Call WorkingSetCommon::toStatusString() to convert the object
* to a loggable format.
*
* objOut will be unowned if it's the result of a fetch or a collection scan.
*/
virtual RunnerState getNext(BSONObj* objOut, DiskLoc* dlOut) = 0;
/**
* Will the next call to getNext() return EOF? It's useful to know if the runner is done
* without having to take responsibility for a result.
*/
virtual bool isEOF() = 0;
/**
* Inform the runner about changes to DiskLoc(s) that occur while the runner is yielded.
* The runner must take any actions required to continue operating correctly, including
* broadcasting the invalidation request to the PlanStage tree being run.
*
* Called from CollectionCursorCache::invalidateDocument.
*
* See db/invalidation_type.h for InvalidationType.
*/
virtual void invalidate(const DiskLoc& dl, InvalidationType type) = 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.
*
* The runner must guarantee as a postcondition that future calls to collection() will
* return NULL.
*/
virtual void kill() = 0;
/**
* Save any state required to yield.
*/
virtual void saveState() = 0;
/**
* Restore saved state, possibly after a yield. Return true if the runner is OK, false if
* it was killed.
*/
virtual bool restoreState() = 0;
/**
* Return the NS that the query is running over.
*/
virtual const string& ns() = 0;
/**
* Return the Collection that the query is running over.
*/
virtual const Collection* collection() = 0;
/**
* Returns OK, allocating and filling '*explain' or '*planInfo' with a description of the
* chosen plan, depending on which is non-NULL (one of the two should be NULL). Caller
* takes onwership of either '*explain' and '*planInfo'. Otherwise, returns false
* a detailed error status.
*
* If 'explain' is NULL, then this out-parameter is ignored. Similarly, if 'staticInfo'
* is NULL, then no static debug information is produced.
*/
virtual Status getInfo(TypeExplain** explain, PlanInfo** planInfo) const = 0;
};
} // namespace mongo
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