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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/db/repl/optime.h"
namespace mongo {
/**
* This class allows for the storageEngine to alert the rest of the system about journaled write
* progress.
*
* It has two methods. The first, getToken(), returns a token representing the current progress
* applied to the node. It should be called just prior to making writes durable (usually, syncing a
* journal entry to disk).
*
* The second method, onDurable(), takes this token as an argument and relays to the rest of the
* system that writes through that point have been journaled. All implementations must be prepared
* to receive default-constructed Tokens generated by NoOpJournalListener, in case they are
* activated while a journal commit is in progress.
*/
class JournalListener {
public:
using Token = repl::OpTime;
virtual ~JournalListener() = default;
virtual Token getToken() = 0;
virtual void onDurable(const Token& token) = 0;
};
/**
* The NoOpJournalListener is a trivial implementation of a JournalListener, that does nothing.
* NoOpJournalListener::instance exists simply as a default implementation for storage engines to
* use until they are passed a JournalListener with greater functionality, allowing us to avoid
* checking for JournalListener-nullness.
*/
class NoOpJournalListener : public JournalListener {
public:
virtual ~NoOpJournalListener() = default;
virtual JournalListener::Token getToken() {
return JournalListener::Token();
}
virtual void onDurable(const Token& token) {}
// As this has no state, it is de facto const and can be safely shared freely.
static NoOpJournalListener instance;
};
}
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