1 //===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_ADT_EPOCH_TRACKER_H
17 #define LLVM_ADT_EPOCH_TRACKER_H
25 class DebugEpochBase {
27 void incrementEpoch() {}
32 explicit HandleBase(const DebugEpochBase *) {}
33 bool isHandleInSync() { return true; }
39 /// \brief A base class for data structure classes wishing to make iterators
40 /// ("handles") pointing into themselves fail-fast. When building without
41 /// asserts, this class is empty and does nothing.
43 /// DebugEpochBase does not by itself track handles pointing into itself. The
44 /// expectation is that routines touching the handles will poll on
45 /// isHandleInSync at appropriate points to assert that the handle they're using
48 class DebugEpochBase {
52 DebugEpochBase() : Epoch(0) {}
54 /// \brief Calling incrementEpoch invalidates all handles pointing into the
56 void incrementEpoch() { ++Epoch; }
58 /// \brief The destructor calls incrementEpoch to make use-after-free bugs
59 /// more likely to crash deterministically.
60 ~DebugEpochBase() { incrementEpoch(); }
62 /// \brief A base class for iterator classes ("handles") that wish to poll for
63 /// iterator invalidating modifications in the underlying data structure.
64 /// When LLVM is built without asserts, this class is empty and does nothing.
66 /// HandleBase does not track the parent data structure by itself. It expects
67 /// the routines modifying the data structure to call incrementEpoch when they
68 /// make an iterator-invalidating modification.
71 const uint64_t *EpochAddress;
72 uint64_t EpochAtCreation;
75 HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {}
77 explicit HandleBase(const DebugEpochBase *Parent)
78 : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {}
80 /// \brief Returns true if the DebugEpochBase this Handle is linked to has
81 /// not called incrementEpoch on itself since the creation of this
82 /// HandleBase instance.
83 bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; }
85 /// \brief Returns a pointer to the epoch word stored in the data structure
86 /// this handle points into.
87 const uint64_t *getEpochAddress() const { return EpochAddress; }