1 //===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 /// 9 /// \file 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_EPOCHTRACKER_H 17 #define LLVM_ADT_EPOCHTRACKER_H 18 19 #include "llvm/Config/abi-breaking.h" 20 21 #include <cstdint> 22 23 namespace llvm { 24 25 #if LLVM_ENABLE_ABI_BREAKING_CHECKS 26 27 /// A base class for data structure classes wishing to make iterators 28 /// ("handles") pointing into themselves fail-fast. When building without 29 /// asserts, this class is empty and does nothing. 30 /// 31 /// DebugEpochBase does not by itself track handles pointing into itself. The 32 /// expectation is that routines touching the handles will poll on 33 /// isHandleInSync at appropriate points to assert that the handle they're using 34 /// is still valid. 35 /// 36 class DebugEpochBase { 37 uint64_t Epoch; 38 39 public: 40 DebugEpochBase() : Epoch(0) {} 41 42 /// Calling incrementEpoch invalidates all handles pointing into the 43 /// calling instance. 44 void incrementEpoch() { ++Epoch; } 45 46 /// The destructor calls incrementEpoch to make use-after-free bugs 47 /// more likely to crash deterministically. 48 ~DebugEpochBase() { incrementEpoch(); } 49 50 /// A base class for iterator classes ("handles") that wish to poll for 51 /// iterator invalidating modifications in the underlying data structure. 52 /// When LLVM is built without asserts, this class is empty and does nothing. 53 /// 54 /// HandleBase does not track the parent data structure by itself. It expects 55 /// the routines modifying the data structure to call incrementEpoch when they 56 /// make an iterator-invalidating modification. 57 /// 58 class HandleBase { 59 const uint64_t *EpochAddress; 60 uint64_t EpochAtCreation; 61 62 public: 63 HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {} 64 65 explicit HandleBase(const DebugEpochBase *Parent) 66 : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {} 67 68 /// Returns true if the DebugEpochBase this Handle is linked to has 69 /// not called incrementEpoch on itself since the creation of this 70 /// HandleBase instance. 71 bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; } 72 73 /// Returns a pointer to the epoch word stored in the data structure 74 /// this handle points into. Can be used to check if two iterators point 75 /// into the same data structure. 76 const void *getEpochAddress() const { return EpochAddress; } 77 }; 78 }; 79 80 #else 81 82 class DebugEpochBase { 83 public: 84 void incrementEpoch() {} 85 86 class HandleBase { 87 public: 88 HandleBase() = default; 89 explicit HandleBase(const DebugEpochBase *) {} 90 bool isHandleInSync() const { return true; } 91 const void *getEpochAddress() const { return nullptr; } 92 }; 93 }; 94 95 #endif // LLVM_ENABLE_ABI_BREAKING_CHECKS 96 97 } // namespace llvm 98 99 #endif 100