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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 <algorithm>
#include <boost/intrusive_ptr.hpp>
#include <vector>
#include "mongo/db/exec/document_value/document.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/util/intrusive_counter.h"
namespace mongo {
/**
* This stage takes a stream of input documents and makes them available to multiple consumers. To
* do so, it will batch incoming documents and allow each consumer to consume one batch at a time.
* As a consequence, consumers must be able to pause their execution to allow other consumers to
* process the batch before moving to the next batch.
*/
class TeeBuffer : public RefCountable {
public:
/**
* Creates a TeeBuffer that will make results available to 'nConsumers' consumers. Note that
* 'bufferSizeBytes' is a soft cap, and may be exceeded by one document's worth (~16MB).
*/
static boost::intrusive_ptr<TeeBuffer> create(
size_t nConsumers, int bufferSizeBytes = internalQueryFacetBufferSizeBytes.load());
void setSource(DocumentSource* source) {
_source = source;
}
/**
* Removes 'consumerId' as a consumer of this buffer. This is required to be called if a
* consumer will not consume all input.
*/
void dispose(size_t consumerId) {
_consumers[consumerId].stillInUse = false;
_consumers[consumerId].nLeftToReturn = 0;
if (std::none_of(_consumers.begin(), _consumers.end(), [](const ConsumerInfo& info) {
return info.stillInUse;
})) {
_buffer.clear();
if (_source) {
_source->dispose();
}
}
}
/**
* Retrieves the next document meant to be consumed by the pipeline given by 'consumerId'.
* Returns GetNextState::ResultState::kPauseExecution if this pipeline has consumed the whole
* buffer, but other consumers are still using it.
*/
DocumentSource::GetNextResult getNext(size_t consumerId);
private:
TeeBuffer(size_t nConsumers, size_t bufferSizeBytes);
/**
* Clears '_buffer', then keeps requesting results from '_source' and pushing them all into
* '_buffer', until more than '_bufferSizeBytes' of documents have been returned, or until
* '_source' is exhausted.
*/
void loadNextBatch();
DocumentSource* _source = nullptr;
const size_t _bufferSizeBytes;
std::vector<DocumentSource::GetNextResult> _buffer;
struct ConsumerInfo {
bool stillInUse = true;
int nLeftToReturn = 0;
};
std::vector<ConsumerInfo> _consumers;
};
} // namespace mongo
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