1
0
mirror of https://github.com/facebook/rocksdb.git synced 2026-10-23 08:09:02 +03:00
Files
rocksdb/db/db_impl/compacted_db_impl.h
Josh Kang 4b983da055 Spell out special member functions (rule of five) (#15387)
Summary:
Pull Request resolved: https://github.com/facebook/rocksdb/pull/15387

## Summary

RocksDB's `.clang-tidy` enables `cppcoreguidelines-special-member-functions`,
`cppcoreguidelines-virtual-class-destructor` and the noexcept-move checks,
and clang warns `-Wdeprecated-copy-with-user-provided-dtor`. A full scan
reports 476 findings. In most of them, a class declares a destructor (or
copy operations) but leaves the rest of copy/move implicit. That has two
costs. Readers can't tell whether a class may be copied or moved. And
resource-owning classes keep an implicit copy that would double-free if
anyone ever used it. This diff resolves 453 of the 476.

Approach, picked per class from least to most invasive:
1. An empty user-provided destructor becomes `= default`. This covers most
   interface classes, such as `virtual ~X() {}` -> `= default`. If the
   class is still copied, that would only rename the deprecated-copy
   warning, so the destructor is removed instead when nothing needs it
   (`Customizable`, `TableFactory` and `InternalKeyComparator` inherit a
   virtual one; `IteratorWrapperBase` isn't polymorphic), and
   `MemTableRep::KeyComparator` gets defaulted copy and move.
2. Classes whose copy is already deleted get explicitly deleted move
   operations too. Move was already unavailable, so this only documents
   it.
3. Resource-owning classes that are never copied get deleted copy and move
   operations. Examples: the C API wrapper structs, which run a
   `destructor_` callback (edited in `tools/c_api_gen/c_base.cc` and
   regenerated into `db/c.cc`); `ShardedCache`, which frees its shards;
   iterator wrappers; and RAII handles.
4. Value types that are copied or moved get the missing operations as
   `= default`, which keeps their current behavior.
5. Exception specifications of existing functions are unchanged, except
   for `WriteBatch`'s move assignment (below): no other `noexcept` is
   added or removed. Only the move operations this diff
   newly declares (`Comparator`, `FileSampledStats` and the thread-local
   `Entry`) are `noexcept`; they copy only scalars or atomics.

`WriteBatch`'s copy and move assignment destroyed `*this` and
placement-new'ed a new `WriteBatch` over it. That is undefined behavior
when `*this` is a subclass, and if the copy constructor threw, `*this`
was left destroyed and was later destroyed again. Move assignment now
assigns member-wise and ends in the same state as the move constructor,
which leaves `has_key_with_ts_`, the timestamp-size tracking and the
other fields it doesn't copy at their defaults. `rep_` is swapped through
a temporary, because a plain string move-assignment can keep the old
buffer (e.g. a large batch reset with `batch = WriteBatch()` would keep
its memory). Nothing in it can throw, so it is now `noexcept`. Copy
assignment copies into a temporary and moves it in, so a throwing copy
leaves `*this` unchanged.

Bugs this exposed and fixed:
- `RestoreAfterCopyOrCreateWorkItem` (backup engine): the hand-written
  move constructor and assignment moved only some fields, so `from_file`
  and `to_file` were empty after `push_back(std::move(...))`. A restore
  that hit a checksum mismatch then reported "While restoring  -> : ..."
  without file names. It now uses the compiler-generated moves, which
  are still `noexcept`.
- `ExternalSstFileIngestionJob` lived in a `std::vector`, and its
  destructor frees raw-owned pointers, so the implicit copy used on
  vector reallocation would double-free. Its file batches also point into
  its own inline file storage, so neither a copy nor a move is safe after
  `Prepare()`. Copy and move are now deleted, and `DBImpl` holds jobs
  through `std::unique_ptr`.

Compatibility: no public class loses an operation users can call. Public
interfaces mostly only get `virtual ~X() = default;`.
`WriteBatch`'s move assignment becomes `noexcept`, which is not part of
the mangled name, so the ABI doesn't change.
`SubcompactionJobInfo` and `CompactionJobInfo` intentionally stay C++20
aggregates, so users' aggregate and designated initializers keep
compiling. `Configurable`, `CompareInterface`, `WriteBatchBase`,
`ObjectLibrary::Entry` and `MemTableRep::KeyComparator` declare defaulted
copy and move, and `Customizable` no longer declares a destructor. As a
result, `Configurable` and `Customizable` subclasses that declare no
destructor or copy operations of their own now move their
registered-options list instead of copying it. In-tree, these are the
mutable-options adapters, the table factories, the memory allocators and
test classes; all are held through smart pointers or used in place, and
`Clone()` copies, so none is moved by value.

Not changed (23): `IODebugContext` (custom deep copy plus a
`std::shared_mutex`), `DBWithColumnFamilies` in db_bench (stored in a
`std::vector` with non-movable members), `Snapshot`'s protected virtual
destructor (intended), `ManagedSnapshot`, the `SubcompactionJobInfo` and
`CompactionJobInfo` aggregates, and the 16 noexcept-move-constructor and
noexcept-swap findings on existing functions, including `autovector`'s
move assignment (adding `noexcept` would change their exception
specifications). Copying `ManagedSnapshot` already double-releases the
snapshot. Fixing that needs a real move implementation and is a behavior
change, so it is left for a separate diff.

Reviewed By: rban1

Differential Revision: D123186309

fbshipit-source-id: 6f8e57e233e12199a007407130bb9a1f6d52e8d1
2026-10-12 16:00:09 -07:00

168 lines
6.4 KiB
C++

// 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 <string>
#include <vector>
#include "db/db_impl/db_impl.h"
namespace ROCKSDB_NAMESPACE {
// TODO: Share common structure with DBImplSecondary and DBImplReadOnly
class CompactedDBImpl : public DBImpl {
public:
CompactedDBImpl(const DBOptions& options, const std::string& dbname);
// No copying allowed
CompactedDBImpl(const CompactedDBImpl&) = delete;
void operator=(const CompactedDBImpl&) = delete;
CompactedDBImpl(CompactedDBImpl&&) = delete;
void operator=(CompactedDBImpl&&) = delete;
~CompactedDBImpl() override;
static Status Open(const Options& options, const std::string& dbname,
std::unique_ptr<DB>* dbptr);
// Implementations of the DB interface
using DB::Get;
DECLARE_SYNC_AND_ASYNC_OVERRIDE(Status, Get, const ReadOptions& options,
ColumnFamilyHandle* column_family,
const Slice& key, PinnableSlice* value,
std::string* timestamp);
using DB::GetWithMetadata;
Status GetWithMetadata(const ReadOptions& options,
ColumnFamilyHandle* column_family, const Slice& key,
PinnableSlice* value,
OutputMetadata* output_metadata) override;
using DB::MultiGet;
// Note that CompactedDBImpl::MultiGet is not the optimized version of
// MultiGet to use.
// TODO: optimize CompactedDBImpl::MultiGet, see DBImpl::MultiGet for details.
DECLARE_SYNC_AND_ASYNC_OVERRIDE(void, MultiGet, const ReadOptions& options,
size_t num_keys,
ColumnFamilyHandle** column_families,
const Slice* keys, PinnableSlice* values,
std::string* timestamps, Status* statuses,
const bool sorted_input);
using DB::MultiGetWithMetadata;
void MultiGetWithMetadata(const ReadOptions& options, size_t num_keys,
ColumnFamilyHandle* const* column_families,
const Slice* keys, PinnableSlice* values,
Status* statuses,
MultiGetOutputMetadata* output_metadata,
const bool sorted_input) override;
using DBImpl::Put;
Status Put(const WriteOptions& /*options*/,
ColumnFamilyHandle* /*column_family*/, const Slice& /*key*/,
const Slice& /*value*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DBImpl::PutEntity;
Status PutEntity(const WriteOptions& /* options */,
ColumnFamilyHandle* /* column_family */,
const Slice& /* key */,
const WideColumns& /* columns */) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DBImpl::Merge;
Status Merge(const WriteOptions& /*options*/,
ColumnFamilyHandle* /*column_family*/, const Slice& /*key*/,
const Slice& /*value*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DBImpl::Delete;
Status Delete(const WriteOptions& /*options*/,
ColumnFamilyHandle* /*column_family*/,
const Slice& /*key*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
Status Write(const WriteOptions& /*options*/,
WriteBatch* /*updates*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DBImpl::CompactRange;
Status CompactRange(const CompactRangeOptions& /*options*/,
ColumnFamilyHandle* /*column_family*/,
const Slice* /*begin*/, const Slice* /*end*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
Status DisableFileDeletions() override {
return Status::NotSupported("Not supported in compacted db mode.");
}
Status EnableFileDeletions() override {
return Status::NotSupported("Not supported in compacted db mode.");
}
Status GetLiveFiles(std::vector<std::string>& ret,
uint64_t* manifest_file_size,
bool /*flush_memtable*/) override {
return DBImpl::GetLiveFiles(ret, manifest_file_size,
false /* flush_memtable */);
}
using DBImpl::Flush;
Status Flush(const FlushOptions& /*options*/,
ColumnFamilyHandle* /*column_family*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
Status SyncWAL() override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DB::IngestExternalFile;
Status IngestExternalFile(
ColumnFamilyHandle* /*column_family*/,
const std::vector<std::string>& /*external_files*/,
const IngestExternalFileOptions& /*ingestion_options*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DB::CreateColumnFamilyWithImport;
Status CreateColumnFamilyWithImport(
const ColumnFamilyOptions& /*options*/,
const std::string& /*column_family_name*/,
const ImportColumnFamilyOptions& /*import_options*/,
const std::vector<const ExportImportFilesMetaData*>& /*metadatas*/,
ColumnFamilyHandle** /*handle*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
using DB::ClipColumnFamily;
Status ClipColumnFamily(ColumnFamilyHandle* /*column_family*/,
const Slice& /*begin*/,
const Slice& /*end*/) override {
return Status::NotSupported("Not supported in compacted db mode.");
}
// FIXME: some missing overrides for more "write" functions
// Share with DBImplReadOnly?
protected:
Status FlushForGetLiveFiles(bool /*force_atomic_flush*/) override {
// No-op for read-only DB
return Status::OK();
}
private:
friend class DB;
inline size_t FindFile(const Slice& key);
Status Init(const Options& options);
ColumnFamilyData* cfd_;
Version* version_;
const Comparator* user_comparator_;
LevelFilesBrief files_;
int files_level_{0};
};
} // namespace ROCKSDB_NAMESPACE