1 // Copyright (c) 2011-present, Facebook, Inc. All rights reserved. 2 // This source code is licensed under both the GPLv2 (found in the 3 // COPYING file in the root directory) and Apache 2.0 License 4 // (found in the LICENSE.Apache file in the root directory). 5 // 6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved. 7 // Use of this source code is governed by a BSD-style license that can be 8 // found in the LICENSE file. See the AUTHORS file for names of contributors. 9 10 #pragma once 11 #include <atomic> 12 #include <string> 13 14 #include "env/file_system_tracer.h" 15 #include "port/port.h" 16 #include "rocksdb/env.h" 17 #include "rocksdb/file_system.h" 18 19 namespace ROCKSDB_NAMESPACE { 20 21 // SequentialFileReader is a wrapper on top of Env::SequentialFile. It handles 22 // Buffered (i.e when page cache is enabled) and Direct (with O_DIRECT / page 23 // cache disabled) reads appropriately, and also updates the IO stats. 24 class SequentialFileReader { 25 private: 26 std::string file_name_; 27 FSSequentialFilePtr file_; 28 std::atomic<size_t> offset_{0}; // read offset 29 30 public: 31 explicit SequentialFileReader( 32 std::unique_ptr<FSSequentialFile>&& _file, const std::string& _file_name, 33 const std::shared_ptr<IOTracer>& io_tracer = nullptr) file_name_(_file_name)34 : file_name_(_file_name), 35 file_(std::move(_file), io_tracer, _file_name) {} 36 37 explicit SequentialFileReader( 38 std::unique_ptr<FSSequentialFile>&& _file, const std::string& _file_name, 39 size_t _readahead_size, 40 const std::shared_ptr<IOTracer>& io_tracer = nullptr) file_name_(_file_name)41 : file_name_(_file_name), 42 file_(NewReadaheadSequentialFile(std::move(_file), _readahead_size), 43 io_tracer, _file_name) {} 44 static Status Create(const std::shared_ptr<FileSystem>& fs, 45 const std::string& fname, const FileOptions& file_opts, 46 std::unique_ptr<SequentialFileReader>* reader, 47 IODebugContext* dbg); 48 49 SequentialFileReader(const SequentialFileReader&) = delete; 50 SequentialFileReader& operator=(const SequentialFileReader&) = delete; 51 52 Status Read(size_t n, Slice* result, char* scratch); 53 54 Status Skip(uint64_t n); 55 file()56 FSSequentialFile* file() { return file_.get(); } 57 file_name()58 std::string file_name() { return file_name_; } 59 use_direct_io()60 bool use_direct_io() const { return file_->use_direct_io(); } 61 62 private: 63 // NewReadaheadSequentialFile provides a wrapper over SequentialFile to 64 // always prefetch additional data with every read. 65 static std::unique_ptr<FSSequentialFile> NewReadaheadSequentialFile( 66 std::unique_ptr<FSSequentialFile>&& file, size_t readahead_size); 67 }; 68 } // namespace ROCKSDB_NAMESPACE 69