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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/stdx/mutex.h"
#include "mongo/stdx/thread.h"
namespace mongo {
class OperationContext;
class ServiceContext;
/**
* Periodically refreshes the cache of the balancer configuration on a primary shard.
*/
class PeriodicBalancerSettingsRefresher {
MONGO_DISALLOW_COPYING(PeriodicBalancerSettingsRefresher);
public:
PeriodicBalancerSettingsRefresher(bool isPrimary);
~PeriodicBalancerSettingsRefresher();
/**
* Instantiates an instance of the PeriodicBalancerSettingsRefresher and installs it on the
* specified service context.
*
* This method is not thread-safe and must be called only once when the service is starting.
*/
static void create(ServiceContext* serviceContext, bool isPrimary);
/**
* Retrieves the per-service instance of the PeriodicBalancerSettingsRefresher.
*/
static PeriodicBalancerSettingsRefresher* get(ServiceContext* serviceContext);
/**
* Invoked when the shard server primary enters the 'PRIMARY' state to start the
* PeriodicBalancerSettingsRefresher.
*/
void start();
/**
* Invoked when this node which is currently serving as a 'PRIMARY' steps down.
*
* This method might be called multiple times in succession, which is what happens as a result
* of incomplete transition to primary so it is resilient to that.
*/
void stop();
/**
* Signals shutdown and blocks until the refresher thread has stopped.
*/
void shutdown();
private:
/**
* The main loop that refreshes the cache periodically. This runs in a separate thread.
*/
void _periodicRefresh();
/**
* Use to check whether or not shutdown has been requested for the running thread.
*/
bool _shutDownRequested();
// The background thread to refresh balancer settings
stdx::thread _thread;
// Protects the state below
stdx::mutex _mutex;
// The PeriodicBalancerSettingsRefresher is only active on a primary node.
bool _isPrimary;
// Used to shut down the background thread
bool _isShutdown{false};
};
} // namespace mongo
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