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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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/db/exec/requires_collection_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/index/index_descriptor.h"
namespace mongo {
/**
* A base class for plan stages which require access to a particular index within a particular
* collection. Provides subclasses access to the index's const CollectionPtr&, as well as to catalog
* types representing the index itself such as the IndexDescriptor. This base class is responsible
* for checking that the collection and index are still valid (e.g. have not been dropped) when
* recovering from yield.
*
* Subclasses must implement doSaveStateRequiresIndex() and doRestoreStateRequiresIndex() in order
* to supply custom yield preparation and yield recovery logic.
*/
class RequiresIndexStage : public RequiresCollectionStage {
public:
RequiresIndexStage(const char* stageType,
ExpressionContext* expCtx,
const CollectionPtr& collection,
const IndexDescriptor* indexDescriptor,
WorkingSet* workingSet);
virtual ~RequiresIndexStage() = default;
protected:
/**
* Performs yield preparation specific to a stage which subclasses from RequiresIndexStage.
*/
virtual void doSaveStateRequiresIndex() = 0;
/**
* Performs yield recovery specific to a stage which subclasses from RequiresIndexStage.
*/
virtual void doRestoreStateRequiresIndex() = 0;
void doSaveStateRequiresCollection() override final;
void doRestoreStateRequiresCollection() override final;
const IndexDescriptor* indexDescriptor() const {
return _indexDescriptor;
}
const IndexAccessMethod* indexAccessMethod() const {
return _indexAccessMethod;
}
WorkingSetRegisteredIndexId workingSetIndexId() const {
return _workingSetIndexId;
}
private:
// This is necessary to protect against that case that our index is dropped and then recreated
// during yield. Such an event should cause the query to be killed, since index cursors may have
// pointers into catalog objects that no longer exist. Since indices do not have UUIDs,
// different epochs of the index cannot be distinguished. The weak_ptr allows us to safely
// determine whether the pointed-to object has been destroyed during yield recovery via the
// shared_ptr control block. We need to call `isDropped()` on the index catalog entry after
// locking the weak_ptr to determine whether the index was dropped or destructed during yield.
std::weak_ptr<const IndexCatalogEntry> _weakIndexCatalogEntry;
const IndexDescriptor* _indexDescriptor;
const IndexAccessMethod* _indexAccessMethod;
std::string _indexName;
// An indentifier for the index required by this stage. Any working set member allocated to
// represent an index key from this index must include this id.
WorkingSetRegisteredIndexId _workingSetIndexId;
};
} // namespace mongo
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