1//===--- CrashRecoveryContext.h - Crash Recovery ----------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
10#define LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
11
12#include "llvm/ADT/STLFunctionalExtras.h"
13
14namespace llvm {
15class CrashRecoveryContextCleanup;
16
17/// Crash recovery helper object.
18///
19/// This class implements support for running operations in a safe context so
20/// that crashes (memory errors, stack overflow, assertion violations) can be
21/// detected and control restored to the crashing thread. Crash detection is
22/// purely "best effort", the exact set of failures which can be recovered from
23/// is platform dependent.
24///
25/// Clients make use of this code by first calling
26/// CrashRecoveryContext::Enable(), and then executing unsafe operations via a
27/// CrashRecoveryContext object. For example:
28///
29/// \code
30///    void actual_work(void *);
31///
32///    void foo() {
33///      CrashRecoveryContext CRC;
34///
35///      if (!CRC.RunSafely(actual_work, 0)) {
36///         ... a crash was detected, report error to user ...
37///      }
38///
39///      ... no crash was detected ...
40///    }
41/// \endcode
42///
43/// To assist recovery the class allows specifying set of actions that will be
44/// executed in any case, whether crash occurs or not. These actions may be used
45/// to reclaim resources in the case of crash.
46class CrashRecoveryContext {
47  void *Impl = nullptr;
48  CrashRecoveryContextCleanup *head = nullptr;
49
50public:
51  CrashRecoveryContext();
52  ~CrashRecoveryContext();
53
54  /// Register cleanup handler, which is used when the recovery context is
55  /// finished.
56  /// The recovery context owns the handler.
57  void registerCleanup(CrashRecoveryContextCleanup *cleanup);
58
59  void unregisterCleanup(CrashRecoveryContextCleanup *cleanup);
60
61  /// Enable crash recovery.
62  static void Enable();
63
64  /// Disable crash recovery.
65  static void Disable();
66
67  /// Return the active context, if the code is currently executing in a
68  /// thread which is in a protected context.
69  static CrashRecoveryContext *GetCurrent();
70
71  /// Return true if the current thread is recovering from a crash.
72  static bool isRecoveringFromCrash();
73
74  /// Execute the provided callback function (with the given arguments) in
75  /// a protected context.
76  ///
77  /// \return True if the function completed successfully, and false if the
78  /// function crashed (or HandleCrash was called explicitly). Clients should
79  /// make as little assumptions as possible about the program state when
80  /// RunSafely has returned false.
81  bool RunSafely(function_ref<void()> Fn);
82  bool RunSafely(void (*Fn)(void*), void *UserData) {
83    return RunSafely([&]() { Fn(UserData); });
84  }
85
86  /// Execute the provide callback function (with the given arguments) in
87  /// a protected context which is run in another thread (optionally with a
88  /// requested stack size).
89  ///
90  /// See RunSafely().
91  ///
92  /// On Darwin, if PRIO_DARWIN_BG is set on the calling thread, it will be
93  /// propagated to the new thread as well.
94  bool RunSafelyOnThread(function_ref<void()>, unsigned RequestedStackSize = 0);
95  bool RunSafelyOnThread(void (*Fn)(void*), void *UserData,
96                         unsigned RequestedStackSize = 0) {
97    return RunSafelyOnThread([&]() { Fn(UserData); }, RequestedStackSize);
98  }
99
100  /// Explicitly trigger a crash recovery in the current process, and
101  /// return failure from RunSafely(). This function does not return.
102  [[noreturn]] void HandleExit(int RetCode);
103
104  /// Return true if RetCode indicates that a signal or an exception occurred.
105  static bool isCrash(int RetCode);
106
107  /// Throw again a signal or an exception, after it was catched once by a
108  /// CrashRecoveryContext.
109  static bool throwIfCrash(int RetCode);
110
111  /// In case of a crash, this is the crash identifier.
112  int RetCode = 0;
113
114  /// Selects whether handling of failures should be done in the same way as
115  /// for regular crashes. When this is active, a crash would print the
116  /// callstack, clean-up any temporary files and create a coredump/minidump.
117  bool DumpStackAndCleanupOnFailure = false;
118};
119
120/// Abstract base class of cleanup handlers.
121///
122/// Derived classes override method recoverResources, which makes actual work on
123/// resource recovery.
124///
125/// Cleanup handlers are stored in a double list, which is owned and managed by
126/// a crash recovery context.
127class CrashRecoveryContextCleanup {
128protected:
129  CrashRecoveryContext *context = nullptr;
130  CrashRecoveryContextCleanup(CrashRecoveryContext *context)
131      : context(context) {}
132
133public:
134  bool cleanupFired = false;
135
136  virtual ~CrashRecoveryContextCleanup();
137  virtual void recoverResources() = 0;
138
139  CrashRecoveryContext *getContext() const {
140    return context;
141  }
142
143private:
144  friend class CrashRecoveryContext;
145  CrashRecoveryContextCleanup *prev = nullptr, *next = nullptr;
146};
147
148/// Base class of cleanup handler that controls recovery of resources of the
149/// given type.
150///
151/// \tparam Derived Class that uses this class as a base.
152/// \tparam T Type of controlled resource.
153///
154/// This class serves as a base for its template parameter as implied by
155/// Curiously Recurring Template Pattern.
156///
157/// This class factors out creation of a cleanup handler. The latter requires
158/// knowledge of the current recovery context, which is provided by this class.
159template<typename Derived, typename T>
160class CrashRecoveryContextCleanupBase : public CrashRecoveryContextCleanup {
161protected:
162  T *resource;
163  CrashRecoveryContextCleanupBase(CrashRecoveryContext *context, T *resource)
164      : CrashRecoveryContextCleanup(context), resource(resource) {}
165
166public:
167  /// Creates cleanup handler.
168  /// \param x Pointer to the resource recovered by this handler.
169  /// \return New handler or null if the method was called outside a recovery
170  ///         context.
171  static Derived *create(T *x) {
172    if (x) {
173      if (CrashRecoveryContext *context = CrashRecoveryContext::GetCurrent())
174        return new Derived(context, x);
175    }
176    return nullptr;
177  }
178};
179
180/// Cleanup handler that reclaims resource by calling destructor on it.
181template <typename T>
182class CrashRecoveryContextDestructorCleanup : public
183  CrashRecoveryContextCleanupBase<CrashRecoveryContextDestructorCleanup<T>, T> {
184public:
185  CrashRecoveryContextDestructorCleanup(CrashRecoveryContext *context,
186                                        T *resource)
187      : CrashRecoveryContextCleanupBase<
188            CrashRecoveryContextDestructorCleanup<T>, T>(context, resource) {}
189
190  void recoverResources() override {
191    this->resource->~T();
192  }
193};
194
195/// Cleanup handler that reclaims resource by calling 'delete' on it.
196template <typename T>
197class CrashRecoveryContextDeleteCleanup : public
198  CrashRecoveryContextCleanupBase<CrashRecoveryContextDeleteCleanup<T>, T> {
199public:
200  CrashRecoveryContextDeleteCleanup(CrashRecoveryContext *context, T *resource)
201    : CrashRecoveryContextCleanupBase<
202        CrashRecoveryContextDeleteCleanup<T>, T>(context, resource) {}
203
204  void recoverResources() override { delete this->resource; }
205};
206
207/// Cleanup handler that reclaims resource by calling its method 'Release'.
208template <typename T>
209class CrashRecoveryContextReleaseRefCleanup : public
210  CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>, T> {
211public:
212  CrashRecoveryContextReleaseRefCleanup(CrashRecoveryContext *context,
213                                        T *resource)
214    : CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>,
215          T>(context, resource) {}
216
217  void recoverResources() override { this->resource->Release(); }
218};
219
220/// Helper class for managing resource cleanups.
221///
222/// \tparam T Type of resource been reclaimed.
223/// \tparam Cleanup Class that defines how the resource is reclaimed.
224///
225/// Clients create objects of this type in the code executed in a crash recovery
226/// context to ensure that the resource will be reclaimed even in the case of
227/// crash. For example:
228///
229/// \code
230///    void actual_work(void *) {
231///      ...
232///      std::unique_ptr<Resource> R(new Resource());
233///      CrashRecoveryContextCleanupRegistrar D(R.get());
234///      ...
235///    }
236///
237///    void foo() {
238///      CrashRecoveryContext CRC;
239///
240///      if (!CRC.RunSafely(actual_work, 0)) {
241///         ... a crash was detected, report error to user ...
242///      }
243/// \endcode
244///
245/// If the code of `actual_work` in the example above does not crash, the
246/// destructor of CrashRecoveryContextCleanupRegistrar removes cleanup code from
247/// the current CrashRecoveryContext and the resource is reclaimed by the
248/// destructor of std::unique_ptr. If crash happens, destructors are not called
249/// and the resource is reclaimed by cleanup object registered in the recovery
250/// context by the constructor of CrashRecoveryContextCleanupRegistrar.
251template <typename T, typename Cleanup = CrashRecoveryContextDeleteCleanup<T> >
252class CrashRecoveryContextCleanupRegistrar {
253  CrashRecoveryContextCleanup *cleanup;
254
255public:
256  CrashRecoveryContextCleanupRegistrar(T *x)
257    : cleanup(Cleanup::create(x)) {
258    if (cleanup)
259      cleanup->getContext()->registerCleanup(cleanup);
260  }
261
262  ~CrashRecoveryContextCleanupRegistrar() { unregister(); }
263
264  void unregister() {
265    if (cleanup && !cleanup->cleanupFired)
266      cleanup->getContext()->unregisterCleanup(cleanup);
267    cleanup = nullptr;
268  }
269};
270} // end namespace llvm
271
272#endif // LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
273