LLVM  8.0.0svn
EpochTracker.h
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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 
23 namespace 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 ///
37  uint64_t Epoch;
38 
39 public:
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.
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 
82 class DebugEpochBase {
83 public:
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
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A base class for data structure classes wishing to make iterators ("handles") pointing into themselve...
Definition: EpochTracker.h:36
~DebugEpochBase()
The destructor calls incrementEpoch to make use-after-free bugs more likely to crash deterministicall...
Definition: EpochTracker.h:48
void incrementEpoch()
Calling incrementEpoch invalidates all handles pointing into the calling instance.
Definition: EpochTracker.h:44
A base class for iterator classes ("handles") that wish to poll for iterator invalidating modificatio...
Definition: EpochTracker.h:58
#define UINT64_MAX
Definition: DataTypes.h:83
HandleBase(const DebugEpochBase *Parent)
Definition: EpochTracker.h:65
const void * getEpochAddress() const
Returns a pointer to the epoch word stored in the data structure this handle points into...
Definition: EpochTracker.h:76
bool isHandleInSync() const
Returns true if the DebugEpochBase this Handle is linked to has not called incrementEpoch on itself s...
Definition: EpochTracker.h:71