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/**
* Copyright (C) 2016 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 "mongo/client/connpool.h"
#include "mongo/db/clientcursor.h"
#include "mongo/db/cursor_id.h"
#include "mongo/db/pipeline/document_source.h"
namespace mongo {
class DocumentSourceMergeCursors : public DocumentSource {
public:
struct CursorDescriptor {
CursorDescriptor(ConnectionString connectionString, std::string ns, CursorId cursorId)
: connectionString(std::move(connectionString)),
ns(std::move(ns)),
cursorId(cursorId) {}
ConnectionString connectionString;
std::string ns;
CursorId cursorId;
};
// virtuals from DocumentSource
GetNextResult getNext() final;
const char* getSourceName() const final;
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
StageConstraints constraints() const final {
StageConstraints constraints;
constraints.hostRequirement = HostTypeRequirement::kAnyShardOrMongoS;
constraints.requiredPosition = PositionRequirement::kFirst;
constraints.requiresInputDocSource = false;
constraints.isAllowedInsideFacetStage = false;
return constraints;
}
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
static boost::intrusive_ptr<DocumentSource> create(
std::vector<CursorDescriptor> cursorDescriptors,
const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
/**
* Returns true if all remotes have reported that their cursors are closed.
*/
bool remotesExhausted() const;
/** Returns non-owning pointers to cursors managed by this stage.
* Call this instead of getNext() if you want access to the raw streams.
* This method should only be called at most once.
*/
std::vector<DBClientCursor*> getCursors();
/**
* Returns the next object from the cursor, throwing an appropriate exception if the cursor
* reported an error. This is a better form of DBClientCursor::nextSafe.
*/
static Document nextSafeFrom(DBClientCursor* cursor);
protected:
void doDispose() final;
private:
struct CursorAndConnection {
CursorAndConnection(const CursorDescriptor& cursorDescriptor);
ScopedDbConnection connection;
DBClientCursor cursor;
};
// using list to enable removing arbitrary elements
typedef std::list<std::shared_ptr<CursorAndConnection>> Cursors;
DocumentSourceMergeCursors(std::vector<CursorDescriptor> cursorDescriptors,
const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
// Converts _cursorDescriptors into active _cursors.
void start();
// This is the description of cursors to merge.
const std::vector<CursorDescriptor> _cursorDescriptors;
// These are the actual cursors we are merging. Created lazily.
Cursors _cursors;
Cursors::iterator _currentCursor;
bool _unstarted;
};
} // namespace mongo
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