text: //------------------------------------------------------------------------------
  /*
      This file is part of rippled: https://github.com/ripple/rippled
      Copyright (c) 2012, 2013 Ripple Labs Inc.
  
      Permission to use, copy, modify, and/or distribute this software for any
      purpose  with  or without fee is hereby granted, provided that the above
      copyright notice and this permission notice appear in all copies.
  
      THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
      MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
      ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
      WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
      ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
      OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
  //==============================================================================
  
  #ifndef RIPPLE_APP_PEERS_PEERSET_H_INCLUDED
  #define RIPPLE_APP_PEERS_PEERSET_H_INCLUDED
  
  #include <ripple/app/main/Application.h>
  #include <ripple/beast/clock/abstract_clock.h>
  #include <ripple/beast/utility/Journal.h>
  #include <ripple/overlay/Peer.h>
  #include <boost/asio/basic_waitable_timer.hpp>
  #include <mutex>
  #include <set>
  
  namespace ripple {
  
  /** Supports data retrieval by managing a set of peers.
  
      When desired data (such as a ledger or a transaction set)
      is missing locally it can be obtained by querying connected
      peers. This class manages common aspects of the retrieval.
      Callers maintain the set by adding and removing peers depending
      on whether the peers have useful information.
  
      This class is an "active" object. It maintains its own timer
      and dispatches work to a job queue. Implementations derive
      from this class and override the abstract hook functions in
      the base.
  
      The data is represented by its hash.
  */
  class PeerSet
  {
  public:
      using clock_type = beast::abstract_clock <std::chrono::steady_clock>;
  
      /** Returns the hash of the data we want. */
      uint256 const& getHash () const
      {
          return mHash;
      }
  
      /** Returns true if we got all the data. */
      bool isComplete () const
      {
          return mComplete;
      }
  
      /** Returns false if we failed to get the data. */
      bool isFailed () const
      {
          return mFailed;
      }
  
      /** Returns the number of times we timed out. */
      int getTimeouts () const
      {
          return mTimeouts;
      }
  
      bool isActive ();
  
      /** Called to indicate that forward progress has been made. */
      void progress ()
      {
          mProgress = true;
      }
  
      void touch ()
      {
          mLastAction = m_clock.now();
      }
  
      clock_type::time_point getLastAction () const
      {
          return mLastAction;
      }
  
      /** Insert a peer to the managed set.
          This will call the derived class hook function.
          @return `true` If the peer was added
      */
      bool insert (std::shared_ptr<Peer> const&);
  
      virtual bool isDone () const
      {
          return mComplete || mFailed;
      }
  
      Application&
      app()
      {
          return app_;
      }
  
  protected:
      using ScopedLockType = std::unique_lock <std::recursive_mutex>;
  
      PeerSet (Application& app, uint256 const& hash, std::chrono::milliseconds interval,
          clock_type& clock, beast::Journal journal);
  
      virtual ~PeerSet() = 0;
  
      virtual void newPeer (std::shared_ptr<Peer> const&) = 0;
  
      virtual void onTimer (bool progress, ScopedLockType&) = 0;
  
      virtual void execute () = 0;
  
      virtual std::weak_ptr<PeerSet> pmDowncast () = 0;
  
      bool isProgress ()
      {
          return mProgress;
      }
  
      void setComplete ()
      {
          mComplete = true;
      }
      void setFailed ()
      {
          mFailed = true;
      }
  
      void invokeOnTimer ();
  
      void sendRequest (const protocol::TMGetLedger& message);
  
      void sendRequest (const protocol::TMGetLedger& message, std::shared_ptr<Peer> const& peer);
  
      void setTimer ();
  
      std::size_t getPeerCount () const;
  
  protected:
      Application& app_;
      beast::Journal m_journal;
      clock_type& m_clock;
  
      std::recursive_mutex mLock;
  
      uint256 mHash;
      std::chrono::milliseconds mTimerInterval;
      int mTimeouts;
      bool mComplete;
      bool mFailed;
      clock_type::time_point mLastAction;
      bool mProgress;
  
      // VFALCO TODO move the responsibility for the timer to a higher level
      boost::asio::basic_waitable_timer<std::chrono::steady_clock> mTimer;
  
      // The identifiers of the peers we are tracking.
      std::set <Peer::id_t> mPeers;
  };
  
  } // ripple
  
  #endif
  