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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
84 lines
2.2 KiB
C++
84 lines
2.2 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#pragma once
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#include "monitoring/perf_level_imp.h"
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#include "monitoring/statistics_impl.h"
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#include "rocksdb/system_clock.h"
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namespace ROCKSDB_NAMESPACE {
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class PerfStepTimer {
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public:
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explicit PerfStepTimer(
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uint64_t* metric, SystemClock* clock = nullptr, bool use_cpu_time = false,
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PerfLevel enable_level = PerfLevel::kEnableTimeExceptForMutex,
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Statistics* statistics = nullptr, uint32_t ticker_type = 0)
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: perf_counter_enabled_(perf_level >= enable_level),
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use_cpu_time_(use_cpu_time),
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ticker_type_(ticker_type),
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clock_((perf_counter_enabled_ || statistics != nullptr)
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? (clock ? clock : SystemClock::Default().get())
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: nullptr),
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start_(0),
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metric_(metric),
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statistics_(statistics) {}
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// No copying allowed
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PerfStepTimer(const PerfStepTimer&) = delete;
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PerfStepTimer& operator=(const PerfStepTimer&) = delete;
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PerfStepTimer(PerfStepTimer&&) = delete;
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PerfStepTimer& operator=(PerfStepTimer&&) = delete;
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~PerfStepTimer() { Stop(); }
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void Start() {
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if (perf_counter_enabled_ || statistics_ != nullptr) {
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start_ = time_now();
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}
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}
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void Measure() {
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if (start_) {
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uint64_t now = time_now();
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*metric_ += now - start_;
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start_ = now;
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}
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}
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void Stop() {
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if (start_) {
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uint64_t duration = time_now() - start_;
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if (perf_counter_enabled_) {
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*metric_ += duration;
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}
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if (statistics_ != nullptr) {
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RecordTick(statistics_, ticker_type_, duration);
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}
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start_ = 0;
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}
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}
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private:
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uint64_t time_now() {
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if (!use_cpu_time_) {
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return clock_->NowNanos();
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} else {
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return clock_->CPUNanos();
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}
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}
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const bool perf_counter_enabled_;
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const bool use_cpu_time_;
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uint32_t ticker_type_;
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SystemClock* const clock_;
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uint64_t start_;
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uint64_t* metric_;
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Statistics* statistics_;
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};
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} // namespace ROCKSDB_NAMESPACE
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