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
21#include <cstdint>
22
23namespace 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///
36class DebugEpochBase {
37 uint64_t Epoch;
38
39public:
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
82class DebugEpochBase {
83public:
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