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// 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).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <atomic>
#include <string>
#include "env/file_system_tracer.h"
#include "port/port.h"
#include "rocksdb/env.h"
#include "rocksdb/file_system.h"
namespace ROCKSDB_NAMESPACE {
// SequentialFileReader is a wrapper on top of Env::SequentialFile. It handles
// Buffered (i.e when page cache is enabled) and Direct (with O_DIRECT / page
// cache disabled) reads appropriately, and also updates the IO stats.
class SequentialFileReader {
private:
#ifndef ROCKSDB_LITE
void NotifyOnFileReadFinish(
uint64_t offset, size_t length,
const FileOperationInfo::StartTimePoint& start_ts,
const FileOperationInfo::FinishTimePoint& finish_ts,
const Status& status) const {
FileOperationInfo info(FileOperationType::kRead, file_name_, start_ts,
finish_ts, status);
info.offset = offset;
info.length = length;
for (auto& listener : listeners_) {
listener->OnFileReadFinish(info);
}
info.status.PermitUncheckedError();
}
void AddFileIOListeners(
const std::vector<std::shared_ptr<EventListener>>& listeners) {
std::for_each(listeners.begin(), listeners.end(),
[this](const std::shared_ptr<EventListener>& e) {
if (e->ShouldBeNotifiedOnFileIO()) {
listeners_.emplace_back(e);
}
});
}
#endif // ROCKSDB_LITE
bool ShouldNotifyListeners() const { return !listeners_.empty(); }
std::string file_name_;
FSSequentialFilePtr file_;
std::atomic<size_t> offset_{0}; // read offset
std::vector<std::shared_ptr<EventListener>> listeners_{};
RateLimiter* rate_limiter_;
public:
explicit SequentialFileReader(
std::unique_ptr<FSSequentialFile>&& _file, const std::string& _file_name,
const std::shared_ptr<IOTracer>& io_tracer = nullptr,
const std::vector<std::shared_ptr<EventListener>>& listeners = {},
RateLimiter* rate_limiter =
nullptr) // TODO: migrate call sites to provide rate limiter
: file_name_(_file_name),
file_(std::move(_file), io_tracer, _file_name),
listeners_(),
rate_limiter_(rate_limiter) {
#ifndef ROCKSDB_LITE
AddFileIOListeners(listeners);
#else
(void)listeners;
#endif
}
explicit SequentialFileReader(
std::unique_ptr<FSSequentialFile>&& _file, const std::string& _file_name,
size_t _readahead_size,
const std::shared_ptr<IOTracer>& io_tracer = nullptr,
const std::vector<std::shared_ptr<EventListener>>& listeners = {},
RateLimiter* rate_limiter =
nullptr) // TODO: migrate call sites to provide rate limiter
: file_name_(_file_name),
file_(NewReadaheadSequentialFile(std::move(_file), _readahead_size),
io_tracer, _file_name),
listeners_(),
rate_limiter_(rate_limiter) {
#ifndef ROCKSDB_LITE
AddFileIOListeners(listeners);
#else
(void)listeners;
#endif
}
static IOStatus Create(const std::shared_ptr<FileSystem>& fs,
const std::string& fname, const FileOptions& file_opts,
std::unique_ptr<SequentialFileReader>* reader,
IODebugContext* dbg, RateLimiter* rate_limiter);
SequentialFileReader(const SequentialFileReader&) = delete;
SequentialFileReader& operator=(const SequentialFileReader&) = delete;
// `rate_limiter_priority` is used to charge the internal rate limiter when
// enabled. The special value `Env::IO_TOTAL` makes this operation bypass the
// rate limiter. The amount charged to the internal rate limiter is n, even
// when less than n bytes are actually read (e.g. at end of file). To avoid
// overcharging the rate limiter, the caller can use file size to cap n to
// read until end of file.
IOStatus Read(size_t n, Slice* result, char* scratch,
Env::IOPriority rate_limiter_priority);
IOStatus Skip(uint64_t n);
FSSequentialFile* file() { return file_.get(); }
std::string file_name() { return file_name_; }
bool use_direct_io() const { return file_->use_direct_io(); }
private:
// NewReadaheadSequentialFile provides a wrapper over SequentialFile to
// always prefetch additional data with every read.
static std::unique_ptr<FSSequentialFile> NewReadaheadSequentialFile(
std::unique_ptr<FSSequentialFile>&& file, size_t readahead_size);
};
} // namespace ROCKSDB_NAMESPACE
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