1//===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file defines the DebugEpochBase and DebugEpochBase::HandleBase classes. 11// These can be used to write iterators that are fail-fast when LLVM is built 12// with asserts enabled. 13// 14//===----------------------------------------------------------------------===// 15 16#ifndef LLVM_ADT_EPOCH_TRACKER_H 17#define LLVM_ADT_EPOCH_TRACKER_H 18 19#include "llvm/Config/abi-breaking.h" 20#include "llvm/Config/llvm-config.h" 21 22#include <cstdint> 23 24namespace llvm { 25 26#if LLVM_ENABLE_ABI_BREAKING_CHECKS 27 28/// \brief A base class for data structure classes wishing to make iterators 29/// ("handles") pointing into themselves fail-fast. When building without 30/// asserts, this class is empty and does nothing. 31/// 32/// DebugEpochBase does not by itself track handles pointing into itself. The 33/// expectation is that routines touching the handles will poll on 34/// isHandleInSync at appropriate points to assert that the handle they're using 35/// is still valid. 36/// 37class DebugEpochBase { 38 uint64_t Epoch; 39 40public: 41 DebugEpochBase() : Epoch(0) {} 42 43 /// \brief Calling incrementEpoch invalidates all handles pointing into the 44 /// calling instance. 45 void incrementEpoch() { ++Epoch; } 46 47 /// \brief The destructor calls incrementEpoch to make use-after-free bugs 48 /// more likely to crash deterministically. 49 ~DebugEpochBase() { incrementEpoch(); } 50 51 /// \brief A base class for iterator classes ("handles") that wish to poll for 52 /// iterator invalidating modifications in the underlying data structure. 53 /// When LLVM is built without asserts, this class is empty and does nothing. 54 /// 55 /// HandleBase does not track the parent data structure by itself. It expects 56 /// the routines modifying the data structure to call incrementEpoch when they 57 /// make an iterator-invalidating modification. 58 /// 59 class HandleBase { 60 const uint64_t *EpochAddress; 61 uint64_t EpochAtCreation; 62 63 public: 64 HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {} 65 66 explicit HandleBase(const DebugEpochBase *Parent) 67 : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {} 68 69 /// \brief Returns true if the DebugEpochBase this Handle is linked to has 70 /// not called incrementEpoch on itself since the creation of this 71 /// HandleBase instance. 72 bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; } 73 74 /// \brief Returns a pointer to the epoch word stored in the data structure 75 /// this handle points into. Can be used to check if two iterators point 76 /// into the same data structure. 77 const void *getEpochAddress() const { return EpochAddress; } 78 }; 79}; 80 81#else 82 83class DebugEpochBase { 84public: 85 void incrementEpoch() {} 86 87 class HandleBase { 88 public: 89 HandleBase() = default; 90 explicit HandleBase(const DebugEpochBase *) {} 91 bool isHandleInSync() const { return true; } 92 const void *getEpochAddress() const { return nullptr; } 93 }; 94}; 95 96#endif // LLVM_ENABLE_ABI_BREAKING_CHECKS 97 98} // namespace llvm 99 100#endif 101