text: /**
   *    Copyright (C) 2015 MongoDB Inc.
   *
   *    This program is free software: you can redistribute it and/or  modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    This program is distributed in the hope that it will be useful,
   *    but WITHOUT ANY WARRANTY; without even the implied warranty of
   *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *    GNU Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the GNU Affero General Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #pragma once
  
  #include "mongo/base/status.h"
  #include "mongo/base/status_with.h"
  #include "mongo/db/jsobj.h"
  #include "mongo/db/repl/replication_coordinator.h"
  #include "mongo/executor/task_executor.h"
  #include "mongo/stdx/condition_variable.h"
  #include "mongo/stdx/functional.h"
  #include "mongo/stdx/mutex.h"
  #include "mongo/util/time_support.h"
  
  namespace mongo {
  namespace repl {
  
  /**
   * Once scheduled, the reporter will periodically send the current replication progress, obtained
   * by invoking "_prepareReplSetUpdatePositionCommandFn", to its sync source until it encounters
   * an error.
   *
   * If the sync source cannot accept the current format (used by server versions 3.2.4 and above) of
   * the "replSetUpdatePosition" command, the reporter will not abort and instead downgrade the format
   * of the command it will send upstream.
   *
   * While the reporter is active, it will be in one of three states:
   * 1) triggered and waiting to send command to sync source as soon as possible.
   * 2) waiting for command response from sync source.
   * 3) waiting for at least "_keepAliveInterval" ms before sending command to sync source.
   *
   * Calling trigger() while the reporter is in state 1 or 2 will cause the reporter to immediately
   * send a new command upon receiving a successful command response.
   *
   * Calling trigger() while it is in state 3 sends a command upstream and cancels the current
   * keep alive timeout, resetting the keep alive schedule.
   */
  class Reporter {
      MONGO_DISALLOW_COPYING(Reporter);
  
  public:
      /**
       * Prepares a BSONObj describing an invocation of the replSetUpdatePosition command that can
       * be sent to this node's sync source to update it about our progress in replication.
       *
       * The returned status indicates whether or not the command was created.
       */
      using PrepareReplSetUpdatePositionCommandFn = stdx::function<StatusWith<BSONObj>()>;
  
      Reporter(executor::TaskExecutor* executor,
               PrepareReplSetUpdatePositionCommandFn prepareReplSetUpdatePositionCommandFn,
               const HostAndPort& target,
               Milliseconds keepAliveInterval);
  
      virtual ~Reporter();
  
      /**
       * Returns sync target.
       */
      HostAndPort getTarget() const;
  
      /**
       * Returns an informational string.
       */
      std::string toString() const;
  
      /**
       * Returns keep alive interval.
       * Reporter will periodically send replication status to sync source every "_keepAliveInterval"
       * until an error occurs.
       */
      Milliseconds getKeepAliveInterval() const;
  
      /**
       * Returns true if a remote command has been scheduled (but not completed)
       * with the executor.
       */
      bool isActive() const;
  
      /**
       * Returns true if new data is available while a remote command is in progress.
       * The reporter will schedule a subsequent remote update immediately upon successful
       * completion of the previous command instead of when the keep alive callback runs.
       */
      bool isWaitingToSendReport() const;
  
      /**
       * Cancels both scheduled and active remote command requests.
       * Returns immediately if the Reporter is not active.
       */
      void shutdown();
  
      /**
       * Waits until Reporter is inactive and returns reporter status.
       */
      Status join();
  
      /**
       * Signals to the Reporter that there is new information to be sent to the "_target" server.
       * Returns the _status, indicating any error the Reporter has encountered.
       */
      Status trigger();
  
      // ================== Test support API ===================
  
      /**
       * Returns scheduled time of keep alive timeout handler.
       */
      Date_t getKeepAliveTimeoutWhen_forTest() const;
  
  private:
      /**
       * Returns true if reporter is active.
       */
      bool _isActive_inlock() const;
  
      /**
       * Prepares remote command to be run by the executor.
       */
      StatusWith<BSONObj> _prepareCommand();
  
      /**
       * Schedules remote command to be run by the executor.
       */
      void _sendCommand_inlock(BSONObj commandRequest);
  
      /**
       * Callback for processing response from remote command.
       */
      void _processResponseCallback(const executor::TaskExecutor::RemoteCommandCallbackArgs& rcbd);
  
      /**
       * Callback for preparing and sending remote command.
       */
      void _prepareAndSendCommandCallback(const executor::TaskExecutor::CallbackArgs& args,
                                          bool fromTrigger);
  
      /**
       * Signals end of Reporter work and notifies waiters.
       */
      void _onShutdown_inlock();
  
      // Not owned by us.
      executor::TaskExecutor* const _executor;
  
      // Prepares update command object.
      const PrepareReplSetUpdatePositionCommandFn _prepareReplSetUpdatePositionCommandFn;
  
      // Host to whom the Reporter sends updates.
      const HostAndPort _target;
  
      // Reporter will send updates every "_keepAliveInterval" ms until the reporter is canceled or
      // encounters an error.
      const Milliseconds _keepAliveInterval;
  
      // Protects member data of this Reporter declared below.
      mutable stdx::mutex _mutex;
  
      mutable stdx::condition_variable _condition;
  
      // Stores the most recent Status returned from the executor.
      Status _status = Status::OK();
  
      // _isWaitingToSendReporter is true when Reporter is scheduled to be run by the executor and
      // subsequent updates have come in.
      bool _isWaitingToSendReporter = false;
  
      // Callback handle to the scheduled remote command.
      executor::TaskExecutor::CallbackHandle _remoteCommandCallbackHandle;
  
      // Callback handle to the scheduled task for preparing and sending the remote command.
      executor::TaskExecutor::CallbackHandle _prepareAndSendCommandCallbackHandle;
  
      // Keep alive timeout callback will not run before this time.
      // If this date is Date_t(), the callback is either unscheduled or canceled.
      // Used for testing only.
      Date_t _keepAliveTimeoutWhen;
  };
  
  }  // namespace repl
  }  // namespace mongo
  