LCOV - code coverage report
Current view: top level - include/llvm/Support - CrashRecoveryContext.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 104 154 67.5 %
Date: 2018-10-16 05:50:02 Functions: 35 56 62.5 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===--- CrashRecoveryContext.h - Crash Recovery ----------------*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : 
      10             : #ifndef LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
      11             : #define LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H
      12             : 
      13             : #include "llvm/ADT/STLExtras.h"
      14             : 
      15             : namespace llvm {
      16             : class CrashRecoveryContextCleanup;
      17             : 
      18             : /// Crash recovery helper object.
      19             : ///
      20             : /// This class implements support for running operations in a safe context so
      21             : /// that crashes (memory errors, stack overflow, assertion violations) can be
      22             : /// detected and control restored to the crashing thread. Crash detection is
      23             : /// purely "best effort", the exact set of failures which can be recovered from
      24             : /// is platform dependent.
      25             : ///
      26             : /// Clients make use of this code by first calling
      27             : /// CrashRecoveryContext::Enable(), and then executing unsafe operations via a
      28             : /// CrashRecoveryContext object. For example:
      29             : ///
      30             : /// \code
      31             : ///    void actual_work(void *);
      32             : ///
      33             : ///    void foo() {
      34             : ///      CrashRecoveryContext CRC;
      35             : ///
      36             : ///      if (!CRC.RunSafely(actual_work, 0)) {
      37             : ///         ... a crash was detected, report error to user ...
      38             : ///      }
      39             : ///
      40             : ///      ... no crash was detected ...
      41             : ///    }
      42             : /// \endcode
      43             : ///
      44             : /// To assist recovery the class allows specifying set of actions that will be
      45             : /// executed in any case, whether crash occurs or not. These actions may be used
      46             : /// to reclaim resources in the case of crash.
      47             : class CrashRecoveryContext {
      48             :   void *Impl;
      49             :   CrashRecoveryContextCleanup *head;
      50             : 
      51             : public:
      52        3786 :   CrashRecoveryContext() : Impl(nullptr), head(nullptr) {}
      53             :   ~CrashRecoveryContext();
      54             : 
      55             :   /// Register cleanup handler, which is used when the recovery context is
      56             :   /// finished.
      57             :   /// The recovery context owns the handler.
      58             :   void registerCleanup(CrashRecoveryContextCleanup *cleanup);
      59             : 
      60             :   void unregisterCleanup(CrashRecoveryContextCleanup *cleanup);
      61             : 
      62             :   /// Enable crash recovery.
      63             :   static void Enable();
      64             : 
      65             :   /// Disable crash recovery.
      66             :   static void Disable();
      67             : 
      68             :   /// Return the active context, if the code is currently executing in a
      69             :   /// thread which is in a protected context.
      70             :   static CrashRecoveryContext *GetCurrent();
      71             : 
      72             :   /// Return true if the current thread is recovering from a crash.
      73             :   static bool isRecoveringFromCrash();
      74             : 
      75             :   /// Execute the provided callback function (with the given arguments) in
      76             :   /// a protected context.
      77             :   ///
      78             :   /// \return True if the function completed successfully, and false if the
      79             :   /// function crashed (or HandleCrash was called explicitly). Clients should
      80             :   /// make as little assumptions as possible about the program state when
      81             :   /// RunSafely has returned false.
      82             :   bool RunSafely(function_ref<void()> Fn);
      83             :   bool RunSafely(void (*Fn)(void*), void *UserData) {
      84             :     return RunSafely([&]() { Fn(UserData); });
      85             :   }
      86             : 
      87             :   /// Execute the provide callback function (with the given arguments) in
      88             :   /// a protected context which is run in another thread (optionally with a
      89             :   /// requested stack size).
      90             :   ///
      91             :   /// See RunSafely() and llvm_execute_on_thread().
      92             :   ///
      93             :   /// On Darwin, if PRIO_DARWIN_BG is set on the calling thread, it will be
      94             :   /// propagated to the new thread as well.
      95             :   bool RunSafelyOnThread(function_ref<void()>, unsigned RequestedStackSize = 0);
      96             :   bool RunSafelyOnThread(void (*Fn)(void*), void *UserData,
      97             :                          unsigned RequestedStackSize = 0) {
      98             :     return RunSafelyOnThread([&]() { Fn(UserData); }, RequestedStackSize);
      99             :   }
     100             : 
     101             :   /// Explicitly trigger a crash recovery in the current process, and
     102             :   /// return failure from RunSafely(). This function does not return.
     103             :   void HandleCrash();
     104             : };
     105             : 
     106             : /// Abstract base class of cleanup handlers.
     107             : ///
     108             : /// Derived classes override method recoverResources, which makes actual work on
     109             : /// resource recovery.
     110             : ///
     111             : /// Cleanup handlers are stored in a double list, which is owned and managed by
     112             : /// a crash recovery context.
     113             : class CrashRecoveryContextCleanup {
     114             : protected:
     115             :   CrashRecoveryContext *context;
     116             :   CrashRecoveryContextCleanup(CrashRecoveryContext *context)
     117       11665 :       : context(context), cleanupFired(false) {}
     118             : 
     119             : public:
     120             :   bool cleanupFired;
     121             : 
     122             :   virtual ~CrashRecoveryContextCleanup();
     123             :   virtual void recoverResources() = 0;
     124             : 
     125           0 :   CrashRecoveryContext *getContext() const {
     126           0 :     return context;
     127             :   }
     128             : 
     129             : private:
     130             :   friend class CrashRecoveryContext;
     131             :   CrashRecoveryContextCleanup *prev, *next;
     132             : };
     133             : 
     134             : /// Base class of cleanup handler that controls recovery of resources of the
     135             : /// given type.
     136             : ///
     137             : /// \tparam Derived Class that uses this class as a base.
     138             : /// \tparam T Type of controlled resource.
     139             : ///
     140             : /// This class serves as a base for its template parameter as implied by
     141             : /// Curiously Recurring Template Pattern.
     142             : ///
     143             : /// This class factors out creation of a cleanup handler. The latter requires
     144             : /// knowledge of the current recovery context, which is provided by this class.
     145             : template<typename Derived, typename T>
     146             : class CrashRecoveryContextCleanupBase : public CrashRecoveryContextCleanup {
     147             : protected:
     148             :   T *resource;
     149       11663 :   CrashRecoveryContextCleanupBase(CrashRecoveryContext *context, T *resource)
     150        9085 :       : CrashRecoveryContextCleanup(context), resource(resource) {}
     151             : 
     152             : public:
     153             :   /// Creates cleanup handler.
     154             :   /// \param x Pointer to the resource recovered by this handler.
     155             :   /// \return New handler or null if the method was called outside a recovery
     156             :   ///         context.
     157       92843 :   static Derived *create(T *x) {
     158       92843 :     if (x) {
     159       80469 :       if (CrashRecoveryContext *context = CrashRecoveryContext::GetCurrent())
     160       11663 :         return new Derived(context, x);
     161             :     }
     162             :     return nullptr;
     163             :   }
     164       40246 : };
     165       40246 : 
     166       37610 : /// Cleanup handler that reclaims resource by calling destructor on it.
     167        3555 : template <typename T>
     168             : class CrashRecoveryContextDestructorCleanup : public
     169             :   CrashRecoveryContextCleanupBase<CrashRecoveryContextDestructorCleanup<T>, T> {
     170             : public:
     171       42032 :   CrashRecoveryContextDestructorCleanup(CrashRecoveryContext *context,
     172       42032 :                                         T *resource)
     173       32328 :       : CrashRecoveryContextCleanupBase<
     174        3512 :             CrashRecoveryContextDestructorCleanup<T>, T>(context, resource) {}
     175             : 
     176             :   virtual void recoverResources() {
     177             :     this->resource->~T();
     178        5403 :   }
     179        5403 : };
     180        5403 : 
     181        3444 : /// Cleanup handler that reclaims resource by calling 'delete' on it.
     182             : template <typename T>
     183             : class CrashRecoveryContextDeleteCleanup : public
     184             :   CrashRecoveryContextCleanupBase<CrashRecoveryContextDeleteCleanup<T>, T> {
     185        2034 : public:
     186        2034 :   CrashRecoveryContextDeleteCleanup(CrashRecoveryContext *context, T *resource)
     187        2034 :     : CrashRecoveryContextCleanupBase<
     188         144 :         CrashRecoveryContextDeleteCleanup<T>, T>(context, resource) {}
     189             : 
     190           0 :   void recoverResources() override { delete this->resource; }
     191             : };
     192        2977 : 
     193        2977 : /// Cleanup handler that reclaims resource by calling its method 'Release'.
     194        2943 : template <typename T>
     195         974 : class CrashRecoveryContextReleaseRefCleanup : public
     196             :   CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>, T> {
     197             : public:
     198             :   CrashRecoveryContextReleaseRefCleanup(CrashRecoveryContext *context,
     199          34 :                                         T *resource)
     200          34 :     : CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>,
     201          34 :           T>(context, resource) {}
     202          34 : 
     203             :   void recoverResources() override { this->resource->Release(); }
     204             : };
     205             : 
     206             : /// Helper class for managing resource cleanups.
     207             : ///
     208             : /// \tparam T Type of resource been reclaimed.
     209        5257 : /// \tparam Cleanup Class that defines how the resource is reclaimed.
     210             : ///
     211          35 : /// Clients create objects of this type in the code executed in a crash recovery
     212             : /// context to ensure that the resource will be reclaimed even in the case of
     213             : /// crash. For example:
     214             : ///
     215             : /// \code
     216          34 : ///    void actual_work(void *) {
     217             : ///      ...
     218           0 : ///      std::unique_ptr<Resource> R(new Resource());
     219           0 : ///      CrashRecoveryContextCleanupRegistrar D(R.get());
     220           0 : ///      ...
     221             : ///    }
     222         940 : ///
     223        5152 : ///    void foo() {
     224           7 : ///      CrashRecoveryContext CRC;
     225          26 : ///
     226             : ///      if (!CRC.RunSafely(actual_work, 0)) {
     227             : ///         ... a crash was detected, report error to user ...
     228             : ///      }
     229             : /// \endcode
     230         136 : ///
     231             : /// If the code of `actual_work` in the example above does not crash, the
     232           0 : /// destructor of CrashRecoveryContextCleanupRegistrar removes cleanup code from
     233             : /// the current CrashRecoveryContext and the resource is reclaimed by the
     234             : /// destructor of std::unique_ptr. If crash happens, destructors are not called
     235             : /// and the resource is reclaimed by cleanup object registered in the recovery
     236          34 : /// context by the constructor of CrashRecoveryContextCleanupRegistrar.
     237             : template <typename T, typename Cleanup = CrashRecoveryContextDeleteCleanup<T> >
     238           0 : class CrashRecoveryContextCleanupRegistrar {
     239             :   CrashRecoveryContextCleanup *cleanup;
     240             : 
     241             : public:
     242         117 :   CrashRecoveryContextCleanupRegistrar(T *x)
     243         151 :     : cleanup(Cleanup::create(x)) {
     244         117 :     if (cleanup)
     245          76 :       cleanup->getContext()->registerCleanup(cleanup);
     246         117 :   }
     247             : 
     248         117 :   ~CrashRecoveryContextCleanupRegistrar() { unregister(); }
     249             : 
     250           0 :   void unregister() {
     251           0 :     if (cleanup && !cleanup->cleanupFired)
     252           0 :       cleanup->getContext()->unregisterCleanup(cleanup);
     253           0 :     cleanup = nullptr;
     254           0 :   }
     255             : };
     256             : } // end namespace llvm
     257             : 
     258             : #endif // LLVM_SUPPORT_CRASHRECOVERYCONTEXT_H

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