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