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//===--- 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 {

  void *Impl = nullptr;

  CrashRecoveryContextCleanup *head = nullptr;

public:

  CrashRecoveryContext();

  ~CrashRecoveryContext();

  /// Register cleanup handler, which is used when the recovery context is

  /// finished.

  /// The recovery context owns the handler.

  void registerCleanup(CrashRecoveryContextCleanup *cleanup);

  void unregisterCleanup(CrashRecoveryContextCleanup *cleanup);

  /// Enable crash recovery.

  static void Enable();

  /// Disable crash recovery.

  static void Disable();

  /// Return the active context, if the code is currently executing in a

  /// thread which is in a protected context.

  static CrashRecoveryContext *GetCurrent();

  /// Return true if the current thread is recovering from a crash.

  static bool isRecoveringFromCrash();

  /// Execute the provided callback function (with the given arguments) in

  /// a protected context.

  ///

  /// \return True if the function completed successfully, and false if the

  /// function crashed (or HandleCrash was called explicitly). Clients should

  /// make as little assumptions as possible about the program state when

  /// RunSafely has returned false.

  bool RunSafely(function_ref<void()> Fn);

  bool RunSafely(void (*Fn)(void*), void *UserData) {

    return RunSafely([&]() { Fn(UserData); });

  }

  /// Execute the provide callback function (with the given arguments) in

  /// a protected context which is run in another thread (optionally with a

  /// requested stack size).

  ///

  /// See RunSafely().

  ///

  /// On Darwin, if PRIO_DARWIN_BG is set on the calling thread, it will be

  /// propagated to the new thread as well.

  bool RunSafelyOnThread(function_ref<void()>, unsigned RequestedStackSize = 0);

  bool RunSafelyOnThread(void (*Fn)(void*), void *UserData,

                         unsigned RequestedStackSize = 0) {

    return RunSafelyOnThread([&]() { Fn(UserData); }, RequestedStackSize);

  }

  /// Explicitly trigger a crash recovery in the current process, and

  /// return failure from RunSafely(). This function does not return.

  [[noreturn]] void HandleExit(int RetCode);

  /// Return true if RetCode indicates that a signal or an exception occurred.

  static bool isCrash(int RetCode);

  /// Throw again a signal or an exception, after it was catched once by a

  /// CrashRecoveryContext.

  static bool throwIfCrash(int RetCode);

  /// In case of a crash, this is the crash identifier.

  int RetCode = 0;

  /// Selects whether handling of failures should be done in the same way as

  /// for regular crashes. When this is active, a crash would print the

  /// callstack, clean-up any temporary files and create a coredump/minidump.

  bool DumpStackAndCleanupOnFailure = false;

};

/// 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 {

protected:

  CrashRecoveryContext *context = nullptr;

  CrashRecoveryContextCleanup(CrashRecoveryContext *context)

      : context(context) {}

public:

  bool cleanupFired = false;

  virtual ~CrashRecoveryContextCleanup();

  virtual void recoverResources() = 0;

  CrashRecoveryContext *getContext() const {

    return context;

  }

private:

  friend class CrashRecoveryContext;

  CrashRecoveryContextCleanup *prev = nullptr, *next = nullptr;

};

/// 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 {

protected:

  T *resource;

  CrashRecoveryContextCleanupBase(CrashRecoveryContext *context, T *resource)

      : CrashRecoveryContextCleanup(context), resource(resource) {}

public:

  /// Creates cleanup handler.

  /// \param x Pointer to the resource recovered by this handler.

  /// \return New handler or null if the method was called outside a recovery

  ///         context.

  static Derived *create(T *x) {

    if (x) {

      if (CrashRecoveryContext *context = CrashRecoveryContext::GetCurrent())

        return new Derived(context, x);

    }

    return nullptr;

  }

};

/// Cleanup handler that reclaims resource by calling destructor on it.

template <typename T>

class CrashRecoveryContextDestructorCleanup : public

  CrashRecoveryContextCleanupBase<CrashRecoveryContextDestructorCleanup<T>, T> {

public:

  CrashRecoveryContextDestructorCleanup(CrashRecoveryContext *context,

                                        T *resource)

      : CrashRecoveryContextCleanupBase<

            CrashRecoveryContextDestructorCleanup<T>, T>(context, resource) {}

  void recoverResources() override {

    this->resource->~T();

  }

};

/// Cleanup handler that reclaims resource by calling 'delete' on it.

template <typename T>

class CrashRecoveryContextDeleteCleanup : public

  CrashRecoveryContextCleanupBase<CrashRecoveryContextDeleteCleanup<T>, T> {

public:

  CrashRecoveryContextDeleteCleanup(CrashRecoveryContext *context, T *resource)

    : CrashRecoveryContextCleanupBase<

        CrashRecoveryContextDeleteCleanup<T>, T>(context, resource) {}

  void recoverResources() override { delete this->resource; }

};

/// Cleanup handler that reclaims resource by calling its method 'Release'.

template <typename T>

class CrashRecoveryContextReleaseRefCleanup : public

  CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>, T> {

public:

  CrashRecoveryContextReleaseRefCleanup(CrashRecoveryContext *context,

                                        T *resource)

    : CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>,

          T>(context, resource) {}

  void recoverResources() override { this->resource->Release(); }

};

/// 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 {

  CrashRecoveryContextCleanup *cleanup;

public:

  CrashRecoveryContextCleanupRegistrar(T *x)

    : cleanup(Cleanup::create(x)) {

    if (cleanup)

      cleanup->getContext()->registerCleanup(cleanup);

  }

  ~CrashRecoveryContextCleanupRegistrar() { unregister(); }

  void unregister() {

    if (cleanup && !cleanup->cleanupFired)

      cleanup->getContext()->unregisterCleanup(cleanup);

    cleanup = nullptr;

  }

};

} // end namespace llvm

#endif // LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H