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//===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the DebugEpochBase and DebugEpochBase::HandleBase classes.
// These can be used to write iterators that are fail-fast when LLVM is built
// with asserts enabled.
#include "llvm/Config/abi-breaking.h"
#include <cstdint>
namespace llvm {
/// A base class for data structure classes wishing to make iterators
/// ("handles") pointing into themselves fail-fast. When building without
/// asserts, this class is empty and does nothing.
/// DebugEpochBase does not by itself track handles pointing into itself. The
/// expectation is that routines touching the handles will poll on
/// isHandleInSync at appropriate points to assert that the handle they're using
/// is still valid.
class DebugEpochBase {
uint64_t Epoch;
DebugEpochBase() : Epoch(0) {}
/// Calling incrementEpoch invalidates all handles pointing into the
/// calling instance.
void incrementEpoch() { ++Epoch; }
/// The destructor calls incrementEpoch to make use-after-free bugs
/// more likely to crash deterministically.
~DebugEpochBase() { incrementEpoch(); }
/// A base class for iterator classes ("handles") that wish to poll for
/// iterator invalidating modifications in the underlying data structure.
/// When LLVM is built without asserts, this class is empty and does nothing.
/// HandleBase does not track the parent data structure by itself. It expects
/// the routines modifying the data structure to call incrementEpoch when they
/// make an iterator-invalidating modification.
class HandleBase {
const uint64_t *EpochAddress;
uint64_t EpochAtCreation;
HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {}
explicit HandleBase(const DebugEpochBase *Parent)
: EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {}
/// Returns true if the DebugEpochBase this Handle is linked to has
/// not called incrementEpoch on itself since the creation of this
/// HandleBase instance.
bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; }
/// Returns a pointer to the epoch word stored in the data structure
/// this handle points into. Can be used to check if two iterators point
/// into the same data structure.
const void *getEpochAddress() const { return EpochAddress; }
class DebugEpochBase {
void incrementEpoch() {}
class HandleBase {
HandleBase() = default;
explicit HandleBase(const DebugEpochBase *) {}
bool isHandleInSync() const { return true; }
const void *getEpochAddress() const { return nullptr; }
} // namespace llvm