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// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
/**
* \class ConfigKeeper
* \class memfile
*
* \brief Utility function for live reconfiguration
*
* When many threads want the same config, we don't want each of these threads
* to subscribe on the same config because of the following reasons:
* - No need to put lots of extra load on the config system.
* - Application doesn't know whether all users have the same config version
* at any given time.
*
* This class implements a utility class for handling this.
*/
#pragma once
#include <vespa/vespalib/util/sync.h>
namespace storage {
template<typename ConfigClass>
class ConfigKeeper {
vespalib::Monitor _configLock;
bool _configUpdated; // Set to true if updating config.
std::unique_ptr<ConfigClass> _nextConfig;
ConfigClass _config;
public:
ConfigKeeper() : _configUpdated(false) {}
void updateConfig(const ConfigClass& config) {
vespalib::MonitorGuard lock(_configLock);
_nextConfig.reset(new ConfigClass(config));
_configUpdated = true;
}
void activateNewConfig() {
if (!_configUpdated) return;
vespalib::MonitorGuard lock(_configLock);
_config = *_nextConfig;
_nextConfig.reset(0);
_configUpdated = false;
lock.signal();
}
void waitForAnyActivation() {
vespalib::MonitorGuard lock(_configLock);
while (_configUpdated) lock.wait();
}
ConfigClass* operator->() { return &_config; }
ConfigClass& operator*() { return _config; }
};
} // storage
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