//===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file defines the DebugEpochBase and DebugEpochBase::HandleBase classes. // These can be used to write iterators that are fail-fast when LLVM is built // with asserts enabled. // //===----------------------------------------------------------------------===// #ifndef LLVM_ADT_EPOCH_TRACKER_H #define LLVM_ADT_EPOCH_TRACKER_H #include "llvm/Config/abi-breaking.h" #include <cstdint> namespace llvm { #if LLVM_ENABLE_ABI_BREAKING_CHECKS /// A base class for data structure classes wishing to make iterators /// ("handles") pointing into themselves fail-fast. When building without /// asserts, this class is empty and does nothing. /// /// DebugEpochBase does not by itself track handles pointing into itself. The /// expectation is that routines touching the handles will poll on /// isHandleInSync at appropriate points to assert that the handle they're using /// is still valid. /// class DebugEpochBase { uint64_t Epoch; public: DebugEpochBase() : Epoch(0) {} /// Calling incrementEpoch invalidates all handles pointing into the /// calling instance. void incrementEpoch() { ++Epoch; } /// The destructor calls incrementEpoch to make use-after-free bugs /// more likely to crash deterministically. ~DebugEpochBase() { incrementEpoch(); } /// A base class for iterator classes ("handles") that wish to poll for /// iterator invalidating modifications in the underlying data structure. /// When LLVM is built without asserts, this class is empty and does nothing. /// /// HandleBase does not track the parent data structure by itself. It expects /// the routines modifying the data structure to call incrementEpoch when they /// make an iterator-invalidating modification. /// class HandleBase { const uint64_t *EpochAddress; uint64_t EpochAtCreation; public: HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {} explicit HandleBase(const DebugEpochBase *Parent) : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {} /// Returns true if the DebugEpochBase this Handle is linked to has /// not called incrementEpoch on itself since the creation of this /// HandleBase instance. bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; } /// Returns a pointer to the epoch word stored in the data structure /// this handle points into. Can be used to check if two iterators point /// into the same data structure. const void *getEpochAddress() const { return EpochAddress; } }; }; #else class DebugEpochBase { public: void incrementEpoch() {} class HandleBase { public: HandleBase() = default; explicit HandleBase(const DebugEpochBase *) {} bool isHandleInSync() const { return true; } const void *getEpochAddress() const { return nullptr; } }; }; #endif // LLVM_ENABLE_ABI_BREAKING_CHECKS } // namespace llvm #endif |