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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/base/disallow_copying.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
class ChunkWritesTracker {
public:
/**
* A factor that determines when a chunk should be split. We should split once data *
* kSplitTestFactor > chunkSize (approximately).
*/
static constexpr uint64_t kSplitTestFactor = 5;
/**
* Add more bytes written to the chunk.
*/
void addBytesWritten(uint64_t bytesWritten) {
_bytesWritten.fetchAndAdd(bytesWritten);
}
/**
* Returns the total number of bytes that have been written to the chunk.
*/
uint64_t getBytesWritten() {
return _bytesWritten.loadRelaxed();
}
/**
* Sets the number of bytes in the tracker to zero and returns the number
* of bytes in the tracker prior to clearing it.
*/
uint64_t clearBytesWritten();
/**
* Returns whether or not this chunk is ready to be split based on the
* maximum allowable size of a chunk.
*/
bool shouldSplit(uint64_t maxChunkSize);
/**
* Locks the chunk for splitting, returning false if it is already locked.
* While it is locked, shouldSplit will always return false.
*/
bool acquireSplitLock();
/**
* Releases the lock acquired for splitting.
*/
void releaseSplitLock();
private:
/**
* The number of bytes that have been written to this chunk. May be
* modified concurrently by several threads.
*/
AtomicWord<unsigned long long> _bytesWritten{0};
/**
* Protects _splitState when starting a split.
*/
stdx::mutex _mtx;
/**
* Whether or not a current split is in progress for this chunk.
*/
bool _isLockedForSplitting{false};
};
} // namespace mongo
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