//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include <stdint.h>

#include <atomic>

#include <mutex>

#include "util/autovector.h"

namespace ROCKSDB_NAMESPACE {

class ColumnFamilyData;

// Similar to FlushScheduler, TrimHistoryScheduler is a FIFO queue that keeps

// track of column families whose flushed immutable memtables may need to be

// removed (aka trimmed). The actual trimming may be slightly delayed. Due to

// the use of the mutex and atomic variable, ScheduleWork,

// TakeNextColumnFamily, and, Empty can be called concurrently.

class TrimHistoryScheduler {

 public:

  TrimHistoryScheduler() : is_empty_(true) {}

  // When a column family needs history trimming, add cfd to the FIFO queue

  void ScheduleWork(ColumnFamilyData* cfd);

  // Remove the column family from the queue, the caller is responsible for

  // calling `MemtableList::TrimHistory`

  ColumnFamilyData* TakeNextColumnFamily();

  bool Empty();

  void Clear();

  // Not on critical path, use mutex to ensure thread safety

 private:

  std::atomic<bool> is_empty_;

  autovector<ColumnFamilyData*> cfds_;

  std::mutex checking_mutex_;

};

}  // namespace ROCKSDB_NAMESPACE