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143 lines
3.4 KiB
C++
143 lines
3.4 KiB
C++
#pragma once
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#include <zkutil/ZooKeeper.h>
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#include <functional>
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#include <common/logger_useful.h>
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namespace zkutil
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{
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/** Реализует метод выбора лидера, описанный здесь: http://zookeeper.apache.org/doc/r3.4.5/recipes.html#sc_leaderElection
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*/
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class LeaderElection
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{
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public:
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typedef std::function<void()> LeadershipHandler;
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/** handler вызывается, когда этот экземпляр становится лидером.
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*/
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LeaderElection(const std::string & path_, ZooKeeper & zookeeper_, LeadershipHandler handler_, const std::string & identifier_ = "")
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: path(path_), zookeeper(zookeeper_), handler(handler_), identifier(identifier_),
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shutdown(false), state(WAITING_LEADERSHIP), log(&Logger::get("LeaderElection"))
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{
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node = EphemeralNodeHolder::createSequential(path + "/leader_election-", zookeeper, identifier);
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std::string node_path = node->getPath();
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node_name = node_path.substr(node_path.find_last_of('/') + 1);
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thread = std::thread(&LeaderElection::threadFunction, this);
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}
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enum State
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{
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WAITING_LEADERSHIP,
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LEADER,
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LEADERSHIP_LOST
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};
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/// если возвращает LEADER, то еще sessionTimeoutMs мы будем лидером, даже если порвется соединение с zookeeper
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State getState()
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{
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if (state == LEADER)
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{
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try
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{
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/// возможно, если сессия разорвалась и заново был вызван init
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if (!zookeeper.exists(node->getPath()))
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{
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LOG_WARNING(log, "Leadership lost. Node " << node->getPath() << " doesn't exist.");
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state = LEADERSHIP_LOST;
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}
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}
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catch (const KeeperException & e)
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{
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LOG_WARNING(log, "Leadership lost. e.message() = " << e.message());
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state = LEADERSHIP_LOST;
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}
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}
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return state;
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}
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~LeaderElection()
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{
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shutdown = true;
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event->set();
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thread.join();
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}
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private:
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std::string path;
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ZooKeeper & zookeeper;
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LeadershipHandler handler;
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std::string identifier;
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EphemeralNodeHolderPtr node;
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std::string node_name;
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std::thread thread;
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volatile bool shutdown;
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zkutil::EventPtr event = new Poco::Event();
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State state;
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Logger * log;
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void threadFunction()
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{
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while (!shutdown)
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{
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bool success = false;
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try
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{
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Strings children = zookeeper.getChildren(path);
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std::sort(children.begin(), children.end());
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auto it = std::lower_bound(children.begin(), children.end(), node_name);
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if (it == children.end() || *it != node_name)
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throw Poco::Exception("Assertion failed in LeaderElection");
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if (it == children.begin())
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{
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state = LEADER;
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handler();
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return;
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}
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if (zookeeper.exists(path + "/" + *(it - 1), nullptr, event))
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event->wait();
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success = true;
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}
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catch (const DB::Exception & e)
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{
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LOG_ERROR(log, "Exception in LeaderElection: Code: " << e.code() << ". " << e.displayText() << std::endl
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<< std::endl
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<< "Stack trace:" << std::endl
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<< e.getStackTrace().toString());
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}
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catch (const Poco::Exception & e)
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{
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LOG_ERROR(log, "Poco::Exception in LeaderElection: " << e.code() << ". " << e.displayText());
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}
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catch (const std::exception & e)
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{
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LOG_ERROR(log, "std::exception in LeaderElection: " << e.what());
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}
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catch (...)
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{
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LOG_ERROR(log, "Unknown exception in LeaderElection");
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}
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if (!success)
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event->tryWait(10 * 1000);
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}
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}
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};
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typedef Poco::SharedPtr<LeaderElection> LeaderElectionPtr;
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}
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