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/**
* Copyright (C) 2019-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/operation_context.h"
#include "mongo/platform/atomic_word.h"
namespace mongo {
/**
* The PrepareConflictTracker tracks if a read operation encounters a prepare conflict. If it
* is blocked on a prepare conflict, we will kill the operation during state transitions (step
* up/step down). This will help us avoid deadlocks between prepare conflicts and state transitions.
*/
class PrepareConflictTracker {
public:
static const OperationContext::Decoration<PrepareConflictTracker> get;
/**
* Decoration requires a default constructor.
*/
PrepareConflictTracker() = default;
/**
* Returns whether a read thread is currently blocked on a prepare conflict.
*/
bool isWaitingOnPrepareConflict() const;
/**
* Sets _waitOnPrepareConflict to true after a read thread hits a WT_PREPARE_CONFLICT
* error code.
*/
void beginPrepareConflict(OperationContext* opCtx);
/**
* Sets _waitOnPrepareConflict to false after wiredTigerPrepareConflictRetry returns,
* implying that the read thread is not blocked on a prepare conflict.
*/
void endPrepareConflict(OperationContext* opCtx);
/**
* Returns the total duration of time spent blocked on prepare conflicts.
*/
Microseconds getPrepareConflictDuration();
private:
/**
* Set to true when a read operation is currently blocked on a prepare conflict.
*/
AtomicWord<bool> _waitOnPrepareConflict{false};
/**
* Multiple prepare read conflicts can be hit during the life time of the prepare conflict
* tracker. _prepareConflictStartTime indicates the most recent time a block started due to a
* prepare read conflict.
*/
TickSource::Tick _prepareConflictStartTime{0};
/**
* Stores the total amount of time spent blocked on prepare read conflicts.
*/
AtomicWord<Microseconds> _prepareConflictDuration{Microseconds(0)};
};
} // namespace mongo
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