foundationdb/fdbserver/LeaderElection.h

/*
 * LeaderElection.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2022 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef FDBSERVER_LEADERELECTION_H
#define FDBSERVER_LEADERELECTION_H
#pragma once

#include "fdbrpc/fdbrpc.h"
#include "fdbrpc/Locality.h"
#include "fdbclient/FDBTypes.h"

class ServerCoordinators;

// Participates in the given coordination group's leader election process, nominating the given
// LeaderInterface (presumed to be a local interface) as leader.  The leader election process is
// "sticky" - once a leader becomes leader, as long as its communications with other processes are
// good it will remain leader.  The outKnownLeader variable is updated to reflect a best guess of
// the current leader.  If the proposed interface becomes the leader, the outKnownLeader will be
// set to the proposedInterface, and then if it is displaced by another leader, the return value will
// eventually be set.  If the return value is cancelled, the candidacy or leadership of the proposedInterface
// will eventually end.
template <class LeaderInterface>
Future<Void> tryBecomeLeader(ServerCoordinators const& coordinators,
                             LeaderInterface const& proposedInterface,
                             Reference<AsyncVar<Optional<LeaderInterface>>> const& outKnownLeader,
                             bool hasConnected,
                             Reference<AsyncVar<ClusterControllerPriorityInfo>> const& asyncPriorityInfo);

// Inform all the coordinators that they have been replaced with a new connection string
Future<Void> changeLeaderCoordinators(ServerCoordinators const& coordinators, Value const& forwardingInfo);

#ifndef __INTEL_COMPILER
#pragma region Implementation
#endif // __INTEL_COMPILER

Future<Void> tryBecomeLeaderInternal(ServerCoordinators const& coordinators,
                                     Value const& proposedSerializedInterface,
                                     Reference<AsyncVar<Value>> const& outSerializedLeader,
                                     bool const& hasConnected,
                                     Reference<AsyncVar<ClusterControllerPriorityInfo>> const& asyncPriorityInfo);

template <class LeaderInterface>
Future<Void> tryBecomeLeader(ServerCoordinators const& coordinators,
                             LeaderInterface const& proposedInterface,
                             Reference<AsyncVar<Optional<LeaderInterface>>> const& outKnownLeader,
                             bool hasConnected,
                             Reference<AsyncVar<ClusterControllerPriorityInfo>> const& asyncPriorityInfo) {
	auto serializedInfo = makeReference<AsyncVar<Value>>();
	Future<Void> m = tryBecomeLeaderInternal(coordinators,
	                                         ObjectWriter::toValue(proposedInterface, IncludeVersion()),
	                                         serializedInfo,
	                                         hasConnected,
	                                         asyncPriorityInfo);
	return m || asyncDeserialize(serializedInfo, outKnownLeader);
}

#ifndef __INTEL_COMPILER
#pragma endregion
#endif // __INTEL_COMPILER

#endif