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When a process joins a cluster it fetches the cluster interface. However, not the whole interface is exposed to the client. This mechanism relies on the fact that the serializer keeps the field ordering and doesn't verify the message before parsing it. To make this work, we provide a client type with one member (the ClusterInterface which is exposed to the client and the server). This client interface has the same FileIdentifier as the ClusterControllerFullInterface which has the same first member. This works because FlatBuffers allows for members to be missing.
73 lines
3.1 KiB
C++
73 lines
3.1 KiB
C++
/*
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* MonitorLeader.h
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*
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* This source file is part of the FoundationDB open source project
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*
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* Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FDBCLIENT_MONITORLEADER_H
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#define FDBCLIENT_MONITORLEADER_H
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#pragma once
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#include "fdbclient/FDBTypes.h"
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#include "fdbclient/CoordinationInterface.h"
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#include "fdbclient/ClusterInterface.h"
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#define CLUSTER_FILE_ENV_VAR_NAME "FDB_CLUSTER_FILE"
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class ClientCoordinators;
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template <class LeaderInterface>
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Future<Void> monitorLeader( Reference<ClusterConnectionFile> const& connFile, Reference<AsyncVar<Optional<LeaderInterface>>> const& outKnownLeader, Reference<AsyncVar<int>> connectedCoordinatorsNum = Reference<AsyncVar<int>>() );
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// Monitors the given coordination group's leader election process and provides a best current guess
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// of the current leader. If a leader is elected for long enough and communication with a quorum of
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// coordinators is possible, eventually outKnownLeader will be that leader's interface.
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#pragma region Implementation
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Future<Void> monitorLeaderInternal( Reference<ClusterConnectionFile> const& connFile, Reference<AsyncVar<Value>> const& outSerializedLeaderInfo, Reference<AsyncVar<int>> const& connectedCoordinatorsNum );
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template <class LeaderInterface>
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struct LeaderDeserializer {
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Future<Void> operator()(const Reference<AsyncVar<Value>>& serializedInfo,
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const Reference<AsyncVar<Optional<LeaderInterface>>>& outKnownLeader) {
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return asyncDeserialize(serializedInfo, outKnownLeader);
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}
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};
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Future<Void> asyncDeserializeClusterInterface(const Reference<AsyncVar<Value>>& serializedInfo,
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const Reference<AsyncVar<Optional<ClusterInterface>>>& outKnownLeader);
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template <>
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struct LeaderDeserializer<ClusterInterface> {
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Future<Void> operator()(const Reference<AsyncVar<Value>>& serializedInfo,
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const Reference<AsyncVar<Optional<ClusterInterface>>>& outKnownLeader) {
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return asyncDeserializeClusterInterface(serializedInfo, outKnownLeader);
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}
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};
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template <class LeaderInterface>
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Future<Void> monitorLeader( Reference<ClusterConnectionFile> const& connFile, Reference<AsyncVar<Optional<LeaderInterface>>> const& outKnownLeader, Reference<AsyncVar<int>> connectedCoordinatorsNum ) {
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LeaderDeserializer<LeaderInterface> deserializer;
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Reference<AsyncVar<Value>> serializedInfo( new AsyncVar<Value> );
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Future<Void> m = monitorLeaderInternal( connFile, serializedInfo, connectedCoordinatorsNum );
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return m || deserializer( serializedInfo, outKnownLeader );
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}
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#pragma endregion
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#endif
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