text: // 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 "rocksdb/status.h"
  
  namespace ROCKSDB_NAMESPACE {
  
  class DB;
  
  class PreReleaseCallback {
   public:
    virtual ~PreReleaseCallback() {}
  
    // Will be called while on the write thread after the write to the WAL and
    // before the write to memtable. This is useful if any operation needs to be
    // done before the write gets visible to the readers, or if we want to reduce
    // the overhead of locking by updating something sequentially while we are on
    // the write thread. If the callback fails, this function returns a non-OK
    // status, the sequence number will not be released, and same status will be
    // propagated to all the writers in the write group.
    // seq is the sequence number that is used for this write and will be
    // released.
    // is_mem_disabled is currently used for debugging purposes to assert that
    // the callback is done from the right write queue.
    // If non-zero, log_number indicates the WAL log to which we wrote.
    // index >= 0 specifies the order of callback in the same write thread.
    // total > index specifies the total number of callbacks in the same write
    // thread. Together with index, could be used to reduce the redundant
    // operations among the callbacks.
    virtual Status Callback(SequenceNumber seq, bool is_mem_disabled,
                            uint64_t log_number, size_t index, size_t total) = 0;
  };
  
  }  // namespace ROCKSDB_NAMESPACE
  