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