1 //===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_ADT_EPOCH_TRACKER_H
17 #define LLVM_ADT_EPOCH_TRACKER_H
19 #include "llvm/Config/abi-breaking.h"
25 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
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.
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
36 class DebugEpochBase {
40 DebugEpochBase() : Epoch(0) {}
42 /// Calling incrementEpoch invalidates all handles pointing into the
44 void incrementEpoch() { ++Epoch; }
46 /// The destructor calls incrementEpoch to make use-after-free bugs
47 /// more likely to crash deterministically.
48 ~DebugEpochBase() { incrementEpoch(); }
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.
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.
59 const uint64_t *EpochAddress;
60 uint64_t EpochAtCreation;
63 HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {}
65 explicit HandleBase(const DebugEpochBase *Parent)
66 : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {}
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; }
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; }
82 class DebugEpochBase {
84 void incrementEpoch() {}
88 HandleBase() = default;
89 explicit HandleBase(const DebugEpochBase *) {}
90 bool isHandleInSync() const { return true; }
91 const void *getEpochAddress() const { return nullptr; }
95 #endif // LLVM_ENABLE_ABI_BREAKING_CHECKS