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 <iosfwd>
  #include <memory>
  #include <string>
  #include <utility>
  #include <vector>
  
  #include "mongo/base/disallow_copying.h"
  #include "mongo/base/status.h"
  #include "mongo/base/status_with.h"
  #include "mongo/db/jsobj.h"
  #include "mongo/db/repl/oplog_entry.h"
  #include "mongo/db/service_context.h"
  #include "mongo/executor/task_executor.h"
  #include "mongo/stdx/condition_variable.h"
  #include "mongo/stdx/functional.h"
  #include "mongo/stdx/mutex.h"
  
  namespace mongo {
  namespace repl {
  
  class OpTime;
  
  class MultiApplier {
      MONGO_DISALLOW_COPYING(MultiApplier);
  
  public:
      /**
       * Operations sorted by timestamp in ascending order.
       */
      using Operations = std::vector<OplogEntry>;
  
      using OperationPtrs = std::vector<const OplogEntry*>;
  
      /**
       * Callback function to report final status of applying operations.
       */
      using CallbackFn = stdx::function<void(const Status&)>;
  
      /**
       * Type of function to to apply a single operation. In production, this function
       * would have the same outcome as calling SyncTail::syncApply() (oplog application mode
       * will be embedded in the function implementation).
       */
      using ApplyOperationFn = stdx::function<Status(OperationPtrs*)>;
  
      using MultiApplyFn = stdx::function<StatusWith<OpTime>(
          OperationContext*, MultiApplier::Operations, MultiApplier::ApplyOperationFn)>;
  
      /**
       * Creates MultiApplier in inactive state.
       *
       * Accepts list of oplog entries to apply in 'operations'.
       *
       * The callback function will be invoked (after schedule()) when the applied has
       * successfully applied all the operations or encountered a failure. Failures may occur if
       * we failed to apply an operation; or if the underlying scheduled work item
       * on the replication executor was canceled.
       *
       * It is an error for 'operations' to be empty but individual oplog entries
       * contained in 'operations' are not validated.
       */
      MultiApplier(executor::TaskExecutor* executor,
                   const Operations& operations,
                   const ApplyOperationFn& applyOperation,
                   const MultiApplyFn& multiApply,
                   const CallbackFn& onCompletion);
  
      /**
       * Blocks while applier is active.
       */
      virtual ~MultiApplier();
  
      /**
       * Returns true if the applier has been started (but has not completed).
       */
      bool isActive() const;
  
      /**
       * Starts applier by scheduling initial db work to be run by the executor.
       */
      Status startup() noexcept;
  
      /**
       * Cancels current db work request.
       * Returns immediately if applier is not active.
       *
       * Callback function may be invoked with an ErrorCodes::CallbackCanceled status.
       */
      void shutdown();
  
      /**
       * Waits for active database worker to complete.
       * Returns immediately if applier is not active.
       */
      void join();
  
      // State transitions:
      // PreStart --> Running --> ShuttingDown --> Complete
      // It is possible to skip intermediate states. For example,
      // Calling shutdown() when the cloner has not started will transition from PreStart directly
      // to Complete.
      // This enum class is made public for testing.
      enum class State { kPreStart, kRunning, kShuttingDown, kComplete };
  
      /**
       * Returns current MultiApplier state.
       * For testing only.
       */
      State getState_forTest() const;
  
  private:
      bool _isActive_inlock() const;
  
      /**
       * DB worker callback function - applies all operations.
       */
      void _callback(const executor::TaskExecutor::CallbackArgs& cbd);
      void _finishCallback(const Status& result);
  
      // Not owned by us.
      executor::TaskExecutor* _executor;
  
      Operations _operations;
      ApplyOperationFn _applyOperation;
      MultiApplyFn _multiApply;
      CallbackFn _onCompletion;
  
      // Protects member data of this MultiApplier.
      mutable stdx::mutex _mutex;
  
      stdx::condition_variable _condition;
  
      // Current multi applier state. See comments for State enum class for details.
      State _state = State::kPreStart;
  
      executor::TaskExecutor::CallbackHandle _dbWorkCallbackHandle;
  };
  
  /**
   * Insertion operator for MultiApplier::State. Formats fetcher state for output stream.
   * For testing only.
   */
  std::ostream& operator<<(std::ostream& os, const MultiApplier::State& state);
  
  }  // namespace repl
  }  // namespace mongo
  