text: ////////////////////////////////////////////////////////////////////////////////
  /// DISCLAIMER
  ///
  /// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
  /// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
  ///
  /// 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.
  ///
  /// Copyright holder is ArangoDB GmbH, Cologne, Germany
  ///
  /// @author Max Neunhoeffer
  /// @author Andreas Streichardt
  ////////////////////////////////////////////////////////////////////////////////
  
  #ifndef ARANGOD_CLUSTER_FOLLOWER_INFO_H
  #define ARANGOD_CLUSTER_FOLLOWER_INFO_H 1
  
  #include "ClusterInfo.h"
  
  namespace arangodb {
  
    ////////////////////////////////////////////////////////////////////////////////
  /// @brief a class to track followers that are in sync for a shard
  ////////////////////////////////////////////////////////////////////////////////
  
  class FollowerInfo {
    std::shared_ptr<std::vector<ServerID> const> _followers;
    Mutex                                        _mutex;
    arangodb::LogicalCollection*                 _docColl;
    std::string                                  _theLeader;
       // if the latter is empty, the we are leading
  
   public:
  
    explicit FollowerInfo(arangodb::LogicalCollection* d)
      : _followers(new std::vector<ServerID>()), _docColl(d) { }
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief get information about current followers of a shard.
    //////////////////////////////////////////////////////////////////////////////
  
    std::shared_ptr<std::vector<ServerID> const> get();
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief add a follower to a shard, this is only done by the server side
    /// of the "get-in-sync" capabilities. This reports to the agency under
    /// `/Current` but in asynchronous "fire-and-forget" way. The method
    /// fails silently, if the follower information has since been dropped
    /// (see `dropFollowerInfo` below).
    //////////////////////////////////////////////////////////////////////////////
  
    void add(ServerID const& s);
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief remove a follower from a shard, this is only done by the
    /// server if a synchronous replication request fails. This reports to
    /// the agency under `/Current` but in an asynchronous "fire-and-forget"
    /// way.
    //////////////////////////////////////////////////////////////////////////////
  
    bool remove(ServerID const& s);
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief clear follower list, no changes in agency necesary
    //////////////////////////////////////////////////////////////////////////////
  
    void clear();
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief set leadership
    //////////////////////////////////////////////////////////////////////////////
  
    void setTheLeader(std::string const& who) {
      MUTEX_LOCKER(locker, _mutex);
      _theLeader = who;
    }
  
    //////////////////////////////////////////////////////////////////////////////
    /// @brief get the leader
    //////////////////////////////////////////////////////////////////////////////
  
    std::string getLeader() {
      MUTEX_LOCKER(locker, _mutex);
      return _theLeader;
    }
  
  };
  }  // end namespace arangodb
  
  #endif
  #define ARANGOD_CLUSTER_CLUSTER_INFO_H 1
  