//===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// 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.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_EPOCHTRACKER_H
#define LLVM_ADT_EPOCHTRACKER_H
#include "llvm/Config/abi-breaking.h"
#include <cstdint>
namespace llvm {
#if LLVM_ENABLE_ABI_BREAKING_CHECKS
/// 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 = 0;
public:
DebugEpochBase() = default;
/// 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 = nullptr;
uint64_t EpochAtCreation = UINT64_MAX;
public:
HandleBase() = default;
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; }
};
};
#else
class DebugEpochBase {
public:
void incrementEpoch() {}
class HandleBase {
public:
HandleBase() = default;
explicit HandleBase(const DebugEpochBase *) {}
bool isHandleInSync() const { return true; }
const void *getEpochAddress() const { return nullptr; }
};
};
#endif // LLVM_ENABLE_ABI_BREAKING_CHECKS
} // namespace llvm
#endif