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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
87 lines
2.9 KiB
C++
87 lines
2.9 KiB
C++
// Copyright (c) 2013, 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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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include "monitoring/histogram.h"
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namespace ROCKSDB_NAMESPACE {
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class SystemClock;
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class HistogramWindowingImpl : public Histogram {
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public:
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HistogramWindowingImpl();
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HistogramWindowingImpl(uint64_t num_windows, uint64_t micros_per_window,
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uint64_t min_num_per_window);
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HistogramWindowingImpl(const HistogramWindowingImpl&) = delete;
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HistogramWindowingImpl& operator=(const HistogramWindowingImpl&) = delete;
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HistogramWindowingImpl(HistogramWindowingImpl&&) = delete;
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HistogramWindowingImpl& operator=(HistogramWindowingImpl&&) = delete;
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~HistogramWindowingImpl() override;
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void Clear() override;
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bool Empty() const override;
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void Add(uint64_t value) override;
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void Merge(const Histogram& other) override;
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void Merge(const HistogramWindowingImpl& other);
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std::string ToString() const override;
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const char* Name() const override { return "HistogramWindowingImpl"; }
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uint64_t min() const override { return stats_.min(); }
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uint64_t max() const override { return stats_.max(); }
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uint64_t num() const override { return stats_.num(); }
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double Median() const override;
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double Percentile(double p) const override;
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double Average() const override;
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double StandardDeviation() const override;
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void Data(HistogramData* const data) const override;
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#ifndef NDEBUG
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void TEST_UpdateClock(const std::shared_ptr<SystemClock>& clock) {
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clock_ = clock;
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}
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#endif // NDEBUG
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private:
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void TimerTick();
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void SwapHistoryBucket();
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inline uint64_t current_window() const {
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return current_window_.load(std::memory_order_relaxed);
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}
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inline uint64_t last_swap_time() const {
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return last_swap_time_.load(std::memory_order_relaxed);
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}
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std::shared_ptr<SystemClock> clock_;
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std::mutex mutex_;
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// Aggregated stats over windows_stats_, all the computation is done
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// upon aggregated values
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HistogramStat stats_;
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// This is a circular array representing the latest N time-windows.
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// Each entry stores a time-window of data. Expiration is done
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// on window-based.
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std::unique_ptr<HistogramStat[]> window_stats_;
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std::atomic_uint_fast64_t current_window_;
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std::atomic_uint_fast64_t last_swap_time_;
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// Following parameters are configuable
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uint64_t num_windows_ = 5;
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uint64_t micros_per_window_ = 60000000;
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// By default, don't care about the number of values in current window
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// when decide whether to swap windows or not.
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uint64_t min_num_per_window_ = 0;
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};
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} // namespace ROCKSDB_NAMESPACE
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