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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/exec/collection_scan_common.h"
namespace mongo {
class CollectionTemp;
class DiskLoc;
class ExtentManager;
class NamespaceDetails;
/**
* A CollectionIterator provides an interface for walking over a collection.
* The details of navigating the collection's structure are below this interface.
*/
class CollectionIterator {
public:
virtual ~CollectionIterator() { }
// True if getNext will produce no more data, false otherwise.
virtual bool isEOF() = 0;
// Return the next item from the collection. Returns DiskLoc() if isEOF.
virtual DiskLoc getNext() = 0;
// Can only be called after prepareToYield and before recoverFromYield.
virtual void invalidate(const DiskLoc& dl) = 0;
// Save any state required to resume operation (without crashing) after DiskLoc deletion or
// a collection drop.
virtual void prepareToYield() = 0;
// Returns true if collection still exists, false otherwise.
virtual bool recoverFromYield() = 0;
};
/**
* This class iterates over a non-capped collection identified by 'ns'.
* The collection must exist when the constructor is called.
*
* If start is not DiskLoc(), the iteration begins at that DiskLoc.
*/
class FlatIterator : public CollectionIterator {
public:
FlatIterator(const CollectionTemp* collection, const DiskLoc& start,
const CollectionScanParams::Direction& dir);
virtual ~FlatIterator() { }
virtual bool isEOF();
virtual DiskLoc getNext();
virtual void invalidate(const DiskLoc& dl);
virtual void prepareToYield();
virtual bool recoverFromYield();
private:
// The result returned on the next call to getNext().
DiskLoc _curr;
const CollectionTemp* _collection;
CollectionScanParams::Direction _direction;
};
/**
* This class iterates over a capped collection identified by 'ns'.
* The collection must exist when the constructor is called.
*
* If start is not DiskLoc(), the iteration begins at that DiskLoc.
*
* If tailable is true, getNext() can be called after isEOF. It will use the last valid
* returned DiskLoc and try to find the next record from that.
*/
class CappedIterator : public CollectionIterator {
public:
CappedIterator(const CollectionTemp* collection, const DiskLoc& start, bool tailable,
const CollectionScanParams::Direction& dir);
virtual ~CappedIterator() { }
// If this is a tailable cursor, isEOF could change its mind after a call to getNext().
virtual bool isEOF();
virtual DiskLoc getNext();
virtual void invalidate(const DiskLoc& dl);
virtual void prepareToYield();
virtual bool recoverFromYield();
private:
/**
* Internal collection navigation helper methods.
*/
static DiskLoc getNextCapped(const NamespaceDetails* nsd, const ExtentManager* em,
const DiskLoc& dl, CollectionScanParams::Direction direction );
static DiskLoc prevLoop(const NamespaceDetails* nsd, const ExtentManager* em,
const DiskLoc& curr);
static DiskLoc nextLoop(const NamespaceDetails* nsd, const ExtentManager* em,
const DiskLoc& prev);
// The collection we're iterating over.
const CollectionTemp* _collection;
// The result returned on the next call to getNext().
DiskLoc _curr;
// If we're tailable, we try to progress from the last valid result when we hit the end.
DiskLoc _prev;
bool _tailable;
CollectionScanParams::Direction _direction;
// If invalidate kills the DiskLoc we need to move forward, we kill the iterator. See the
// comment in the body of invalidate(...).
bool _killedByInvalidate;
};
} // namespace mongo
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