LLVM  3.7.0
EpochTracker.h
Go to the documentation of this file.
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 
23 namespace llvm {
24 
25 #ifndef LLVM_ENABLE_ABI_BREAKING_CHECKS
26 
28 public:
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 ///
51 class DebugEpochBase {
52  uint64_t Epoch;
53 
54 public:
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
const void * getEpochAddress() const
Definition: EpochTracker.h:36
HandleBase(const DebugEpochBase *)
Definition: EpochTracker.h:34