llvm/llvm/include/llvm/Support/CrashRecoveryContext.h

//===--- CrashRecoveryContext.h - Crash Recovery ----------------*- 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
#define LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H

#include "llvm/ADT/STLFunctionalExtras.h"

namespace llvm {
class CrashRecoveryContextCleanup;

/// Crash recovery helper object.
///
/// This class implements support for running operations in a safe context so
/// that crashes (memory errors, stack overflow, assertion violations) can be
/// detected and control restored to the crashing thread. Crash detection is
/// purely "best effort", the exact set of failures which can be recovered from
/// is platform dependent.
///
/// Clients make use of this code by first calling
/// CrashRecoveryContext::Enable(), and then executing unsafe operations via a
/// CrashRecoveryContext object. For example:
///
/// \code
///    void actual_work(void *);
///
///    void foo() {
///      CrashRecoveryContext CRC;
///
///      if (!CRC.RunSafely(actual_work, 0)) {
///         ... a crash was detected, report error to user ...
///      }
///
///      ... no crash was detected ...
///    }
/// \endcode
///
/// To assist recovery the class allows specifying set of actions that will be
/// executed in any case, whether crash occurs or not. These actions may be used
/// to reclaim resources in the case of crash.
class CrashRecoveryContext { … };

/// Abstract base class of cleanup handlers.
///
/// Derived classes override method recoverResources, which makes actual work on
/// resource recovery.
///
/// Cleanup handlers are stored in a double list, which is owned and managed by
/// a crash recovery context.
class CrashRecoveryContextCleanup { … };

/// Base class of cleanup handler that controls recovery of resources of the
/// given type.
///
/// \tparam Derived Class that uses this class as a base.
/// \tparam T Type of controlled resource.
///
/// This class serves as a base for its template parameter as implied by
/// Curiously Recurring Template Pattern.
///
/// This class factors out creation of a cleanup handler. The latter requires
/// knowledge of the current recovery context, which is provided by this class.
template<typename Derived, typename T>
class CrashRecoveryContextCleanupBase : public CrashRecoveryContextCleanup { … };

/// Cleanup handler that reclaims resource by calling destructor on it.
template <typename T>
class CrashRecoveryContextDestructorCleanup : public
  CrashRecoveryContextCleanupBase<CrashRecoveryContextDestructorCleanup<T>, T> { … };

/// Cleanup handler that reclaims resource by calling 'delete' on it.
template <typename T>
class CrashRecoveryContextDeleteCleanup : public
  CrashRecoveryContextCleanupBase<CrashRecoveryContextDeleteCleanup<T>, T> { … };

/// Cleanup handler that reclaims resource by calling its method 'Release'.
template <typename T>
class CrashRecoveryContextReleaseRefCleanup : public
  CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>, T> { … };

/// Helper class for managing resource cleanups.
///
/// \tparam T Type of resource been reclaimed.
/// \tparam Cleanup Class that defines how the resource is reclaimed.
///
/// Clients create objects of this type in the code executed in a crash recovery
/// context to ensure that the resource will be reclaimed even in the case of
/// crash. For example:
///
/// \code
///    void actual_work(void *) {
///      ...
///      std::unique_ptr<Resource> R(new Resource());
///      CrashRecoveryContextCleanupRegistrar D(R.get());
///      ...
///    }
///
///    void foo() {
///      CrashRecoveryContext CRC;
///
///      if (!CRC.RunSafely(actual_work, 0)) {
///         ... a crash was detected, report error to user ...
///      }
/// \endcode
///
/// If the code of `actual_work` in the example above does not crash, the
/// destructor of CrashRecoveryContextCleanupRegistrar removes cleanup code from
/// the current CrashRecoveryContext and the resource is reclaimed by the
/// destructor of std::unique_ptr. If crash happens, destructors are not called
/// and the resource is reclaimed by cleanup object registered in the recovery
/// context by the constructor of CrashRecoveryContextCleanupRegistrar.
template <typename T, typename Cleanup = CrashRecoveryContextDeleteCleanup<T> >
class CrashRecoveryContextCleanupRegistrar { … };
} // end namespace llvm

#endif // LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H