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 24 namespace 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 /// 37 class DebugEpochBase { 38 uint64_t Epoch; 39 40 public: 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 83 class DebugEpochBase { 84 public: 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
