//  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 <cassert>

#include <cstdint>

#include <memory>

#include <unordered_map>

#include "file/file_prefetch_buffer.h"

#include "rocksdb/rocksdb_namespace.h"

namespace ROCKSDB_NAMESPACE {

// A class that owns a collection of FilePrefetchBuffers using the file number

// as key. Used for implementing compaction readahead for blob files. Designed

// to be accessed by a single thread only: every (sub)compaction needs its own

// buffers since they are guaranteed to read different blobs from different

// positions even when reading the same file.

class PrefetchBufferCollection {

 public:

  explicit PrefetchBufferCollection(uint64_t readahead_size)

      : readahead_size_(readahead_size) {

    assert(readahead_size_ > 0);

  }

  FilePrefetchBuffer* GetOrCreatePrefetchBuffer(uint64_t file_number);

 private:

  uint64_t readahead_size_;

  std::unordered_map<uint64_t, std::unique_ptr<FilePrefetchBuffer>>

      prefetch_buffers_;  // maps file number to prefetch buffer

};

}  // namespace ROCKSDB_NAMESPACE