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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 <boost/optional.hpp>
#include <memory>
#include "mongo/s/chunk_writes_tracker.h"
namespace mongo {
/**
* Drives state transitions and the status of a ChunkWritesTracker for a chunk
* while it is splitting. Supports cancelability so that we don't lose
* information from the writes tracker if the split errors. Should be created
* when it is decided that a split should be performed and then passed along to
* the ChunkSplitter which will drive these state changes.
*/
class ChunkSplitStateDriver final {
ChunkSplitStateDriver(const ChunkSplitStateDriver&) = delete;
ChunkSplitStateDriver& operator=(const ChunkSplitStateDriver&) = delete;
public:
/**
* Tries to lock the writesTracker for splitting, and if it succeeds,
* constructs and returns a ChunkSplitStateDriver object. If it fails due to the
* writesTracker already being locked, returns boost::none.
*/
static std::shared_ptr<ChunkSplitStateDriver> tryInitiateSplit(
std::shared_ptr<ChunkWritesTracker> writesTracker);
/**
* Sets the other pointer back to default initialized state so that it
* doesn't try to cancel any ongoing split in its destructor. This
* constructor is required for boost::optional.
*/
ChunkSplitStateDriver(ChunkSplitStateDriver&& other) noexcept;
/**
* Not needed.
*/
ChunkSplitStateDriver& operator=(ChunkSplitStateDriver&&) = delete;
/**
* If there's an ongoing split, cancels it. Otherwise does nothing.
*/
~ChunkSplitStateDriver();
/**
* Clears the current bytes written, but stashes them in a variable in case
* the split is later canceled.
*/
void prepareSplit();
/**
* In the case that we trigger a split but decide not to split due to the
* actual size of a chunk on disk being too small, we update our estimate
* by abandoning the stashed bytes we had written prior to prepare. That
* way we won't continue to trigger splits on a chunk that is smaller than
* we currently estimate it to be.
*/
void abandonPrepare();
/**
* Marks the split as committed, which means that shouldSplit will
* never again return true.
*/
void commitSplit();
private:
/**
* Should only be used by tryInitiateSplit
*/
ChunkSplitStateDriver(std::shared_ptr<ChunkWritesTracker> writesTracker)
: _writesTracker(writesTracker), _splitState(SplitState::kSplitInProgress) {}
/**
* Pointer to the writes tracker object for which we're driving the split
*/
std::weak_ptr<ChunkWritesTracker> _writesTracker;
/**
* Carries over result from prepare into cancelSplit.
*/
uint64_t _stashedBytesWritten{0};
/**
* The current state of the chunk with respect to its progress being split.
*/
enum class SplitState {
kNotSplitting,
kSplitInProgress,
kSplitPrepared,
kSplitCommitted,
} _splitState{SplitState::kNotSplitting};
};
} // namespace mongo
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