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/**
* Copyright (C) 2017 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/base/disallow_copying.h"
#include "mongo/db/repl/optime.h"
#include "mongo/s/client/shard.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
/**
* Implements the support for "read your own write" when run on a node of a replica set. Can be used
* in the scenarios where causal consistency is not available yet.
*/
class RSLocalClient {
MONGO_DISALLOW_COPYING(RSLocalClient);
public:
explicit RSLocalClient() = default;
~RSLocalClient() = default;
/**
* Runs the specified command returns the BSON command response plus parsed out Status of this
* response and write concern error (if present).
*/
StatusWith<Shard::CommandResponse> runCommandOnce(OperationContext* opCtx,
const std::string& dbName,
const BSONObj& cmdObj);
/**
* Warning: This method exhausts the cursor and pulls all data into memory.
* Do not use other than for very small (i.e., admin or metadata) collections.
*/
StatusWith<Shard::QueryResponse> queryOnce(OperationContext* opCtx,
const ReadPreferenceSetting& readPref,
const repl::ReadConcernLevel& readConcernLevel,
const NamespaceString& nss,
const BSONObj& query,
const BSONObj& sort,
boost::optional<long long> limit);
private:
/**
* Checks if an OpTime was set on the current Client (ie if the current operation performed a
* write) and if so updates _lastOpTime to the OpTime from the write that was just performed.
* The 'previousOpTimeOnClient' parameter is the optime that *was* the optime on this client
* before we ran this command through this RSLocalClient. By the time this method is called,
* if the optime set on the Client is different than 'previousOpTimeOnClient' then that means
* the command just run did a write and we should update _lastOpTime to capture the optime of
* the write we just did. If the current optime on the client is the same as
* 'previousOpTimeOnClient' then the command we just ran didn't do a write, and we should leave
* _lastOpTime alone.
*/
void _updateLastOpTimeFromClient(OperationContext* opCtx,
const repl::OpTime& previousOpTimeOnClient);
repl::OpTime _getLastOpTime();
// Guards _lastOpTime below.
stdx::mutex _mutex;
// Stores the optime that was generated by the last operation to perform a write that was run
// through _runCommand. Used in _exhaustiveFindOnConfig for waiting for that optime to be
// committed so that readConcern majority reads will read the writes that were performed without
// a w:majority write concern.
repl::OpTime _lastOpTime{};
};
} // namespace mongo
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