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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
103 lines
3.8 KiB
C++
103 lines
3.8 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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// 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 <atomic>
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#include <functional>
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#include <memory>
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#include <unordered_map>
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#include <vector>
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#include "port/port.h"
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#include "util/autovector.h"
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namespace ROCKSDB_NAMESPACE {
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// Cleanup function that will be called for a stored thread local
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// pointer (if not NULL) when one of the following happens:
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// (1) a thread terminates
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// (2) a ThreadLocalPtr is destroyed
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//
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// Warning: this function is called while holding a global mutex. The same mutex
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// is used (at least in some cases) by most methods of ThreadLocalPtr, and it's
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// shared across all instances of ThreadLocalPtr. Thereforere extra care
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// is needed to avoid deadlocks. In particular, the handler shouldn't lock any
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// mutexes and shouldn't call any methods of any ThreadLocalPtr instances,
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// unless you know what you're doing.
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using UnrefHandler = void (*)(void* ptr);
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// ThreadLocalPtr stores only values of pointer type. Different from
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// the usual thread-local-storage, ThreadLocalPtr has the ability to
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// distinguish data coming from different threads and different
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// ThreadLocalPtr instances. For example, if a regular thread_local
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// variable A is declared in DBImpl, two DBImpl objects would share
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// the same A. However, a ThreadLocalPtr that is defined under the
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// scope of DBImpl can avoid such confliction. As a result, its memory
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// usage would be O(# of threads * # of ThreadLocalPtr instances).
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class ThreadLocalPtr {
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public:
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explicit ThreadLocalPtr(UnrefHandler handler = nullptr);
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ThreadLocalPtr(const ThreadLocalPtr&) = delete;
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ThreadLocalPtr& operator=(const ThreadLocalPtr&) = delete;
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ThreadLocalPtr(ThreadLocalPtr&&) = delete;
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ThreadLocalPtr& operator=(ThreadLocalPtr&&) = delete;
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~ThreadLocalPtr();
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// Return the current pointer stored in thread local
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void* Get() const;
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// Set a new pointer value to the thread local storage.
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void Reset(void* ptr);
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// Atomically swap the supplied ptr and return the previous value
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void* Swap(void* ptr);
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// Atomically compare the stored value with expected. Set the new
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// pointer value to thread local only if the comparison is true.
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// Otherwise, expected returns the stored value.
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// Return true on success, false on failure
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bool CompareAndSwap(void* ptr, void*& expected);
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// Reset all thread local data to replacement, and return non-nullptr
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// data for all existing threads
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void Scrape(autovector<void*>* ptrs, void* const replacement);
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using FoldFunc = std::function<void(void*, void*)>;
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// Update res by applying func on each thread-local value. Holds a lock that
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// prevents unref handler from running during this call, but clients must
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// still provide external synchronization since the owning thread can
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// access the values without internal locking, e.g., via Get() and Reset().
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void Fold(FoldFunc func, void* res);
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// Add here for testing
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// Return the next available Id without claiming it
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static uint32_t TEST_PeekId();
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// Initialize the static singletons of the ThreadLocalPtr.
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//
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// If this function is not called, then the singletons will be
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// automatically initialized when they are used.
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//
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// Calling this function twice or after the singletons have been
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// initialized will be no-op.
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static void InitSingletons();
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class StaticMeta;
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private:
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static StaticMeta* Instance();
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const uint32_t id_;
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};
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} // namespace ROCKSDB_NAMESPACE
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