//===- 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

//

//===----------------------------------------------------------------------===//

//

// 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_EPOCH_TRACKER_H

#define LLVM_ADT_EPOCH_TRACKER_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;

public:

  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;

  public:

    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; }

  };

};

#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