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      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 <string>
     14 
     15 namespace llvm {
     16 class StringRef;
     17 
     18 class CrashRecoveryContextCleanup;
     19 
     20 /// \brief Crash recovery helper object.
     21 ///
     22 /// This class implements support for running operations in a safe context so
     23 /// that crashes (memory errors, stack overflow, assertion violations) can be
     24 /// detected and control restored to the crashing thread. Crash detection is
     25 /// purely "best effort", the exact set of failures which can be recovered from
     26 /// is platform dependent.
     27 ///
     28 /// Clients make use of this code by first calling
     29 /// CrashRecoveryContext::Enable(), and then executing unsafe operations via a
     30 /// CrashRecoveryContext object. For example:
     31 ///
     32 ///    void actual_work(void *);
     33 ///
     34 ///    void foo() {
     35 ///      CrashRecoveryContext CRC;
     36 ///
     37 ///      if (!CRC.RunSafely(actual_work, 0)) {
     38 ///         ... a crash was detected, report error to user ...
     39 ///      }
     40 ///
     41 ///      ... no crash was detected ...
     42 ///    }
     43 ///
     44 /// Crash recovery contexts may not be nested.
     45 class CrashRecoveryContext {
     46   void *Impl;
     47   CrashRecoveryContextCleanup *head;
     48 
     49 public:
     50   CrashRecoveryContext() : Impl(0), head(0) {}
     51   ~CrashRecoveryContext();
     52 
     53   void registerCleanup(CrashRecoveryContextCleanup *cleanup);
     54   void unregisterCleanup(CrashRecoveryContextCleanup *cleanup);
     55 
     56   /// \brief Enable crash recovery.
     57   static void Enable();
     58 
     59   /// \brief Disable crash recovery.
     60   static void Disable();
     61 
     62   /// \brief Return the active context, if the code is currently executing in a
     63   /// thread which is in a protected context.
     64   static CrashRecoveryContext *GetCurrent();
     65 
     66   /// \brief Return true if the current thread is recovering from a
     67   /// crash.
     68   static bool isRecoveringFromCrash();
     69 
     70   /// \brief Execute the provide callback function (with the given arguments) in
     71   /// a protected context.
     72   ///
     73   /// \return True if the function completed successfully, and false if the
     74   /// function crashed (or HandleCrash was called explicitly). Clients should
     75   /// make as little assumptions as possible about the program state when
     76   /// RunSafely has returned false. Clients can use getBacktrace() to retrieve
     77   /// the backtrace of the crash on failures.
     78   bool RunSafely(void (*Fn)(void*), void *UserData);
     79 
     80   /// \brief Execute the provide callback function (with the given arguments) in
     81   /// a protected context which is run in another thread (optionally with a
     82   /// requested stack size).
     83   ///
     84   /// See RunSafely() and llvm_execute_on_thread().
     85   bool RunSafelyOnThread(void (*Fn)(void*), void *UserData,
     86                          unsigned RequestedStackSize = 0);
     87 
     88   /// \brief Explicitly trigger a crash recovery in the current process, and
     89   /// return failure from RunSafely(). This function does not return.
     90   void HandleCrash();
     91 
     92   /// \brief Return a string containing the backtrace where the crash was
     93   /// detected; or empty if the backtrace wasn't recovered.
     94   ///
     95   /// This function is only valid when a crash has been detected (i.e.,
     96   /// RunSafely() has returned false.
     97   const std::string &getBacktrace() const;
     98 };
     99 
    100 class CrashRecoveryContextCleanup {
    101 protected:
    102   CrashRecoveryContext *context;
    103   CrashRecoveryContextCleanup(CrashRecoveryContext *context)
    104     : context(context), cleanupFired(false) {}
    105 public:
    106   bool cleanupFired;
    107 
    108   virtual ~CrashRecoveryContextCleanup();
    109   virtual void recoverResources() = 0;
    110 
    111   CrashRecoveryContext *getContext() const {
    112     return context;
    113   }
    114 
    115 private:
    116   friend class CrashRecoveryContext;
    117   CrashRecoveryContextCleanup *prev, *next;
    118 };
    119 
    120 template<typename DERIVED, typename T>
    121 class CrashRecoveryContextCleanupBase : public CrashRecoveryContextCleanup {
    122 protected:
    123   T *resource;
    124   CrashRecoveryContextCleanupBase(CrashRecoveryContext *context, T* resource)
    125     : CrashRecoveryContextCleanup(context), resource(resource) {}
    126 public:
    127   static DERIVED *create(T *x) {
    128     if (x) {
    129       if (CrashRecoveryContext *context = CrashRecoveryContext::GetCurrent())
    130         return new DERIVED(context, x);
    131     }
    132     return 0;
    133   }
    134 };
    135 
    136 template <typename T>
    137 class CrashRecoveryContextDestructorCleanup : public
    138   CrashRecoveryContextCleanupBase<CrashRecoveryContextDestructorCleanup<T>, T> {
    139 public:
    140   CrashRecoveryContextDestructorCleanup(CrashRecoveryContext *context,
    141                                         T *resource)
    142     : CrashRecoveryContextCleanupBase<
    143         CrashRecoveryContextDestructorCleanup<T>, T>(context, resource) {}
    144 
    145   virtual void recoverResources() {
    146     this->resource->~T();
    147   }
    148 };
    149 
    150 template <typename T>
    151 class CrashRecoveryContextDeleteCleanup : public
    152   CrashRecoveryContextCleanupBase<CrashRecoveryContextDeleteCleanup<T>, T> {
    153 public:
    154   CrashRecoveryContextDeleteCleanup(CrashRecoveryContext *context, T *resource)
    155     : CrashRecoveryContextCleanupBase<
    156         CrashRecoveryContextDeleteCleanup<T>, T>(context, resource) {}
    157 
    158   virtual void recoverResources() {
    159     delete this->resource;
    160   }
    161 };
    162 
    163 template <typename T>
    164 class CrashRecoveryContextReleaseRefCleanup : public
    165   CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>, T>
    166 {
    167 public:
    168   CrashRecoveryContextReleaseRefCleanup(CrashRecoveryContext *context,
    169                                         T *resource)
    170     : CrashRecoveryContextCleanupBase<CrashRecoveryContextReleaseRefCleanup<T>,
    171           T>(context, resource) {}
    172 
    173   virtual void recoverResources() {
    174     this->resource->Release();
    175   }
    176 };
    177 
    178 template <typename T, typename Cleanup = CrashRecoveryContextDeleteCleanup<T> >
    179 class CrashRecoveryContextCleanupRegistrar {
    180   CrashRecoveryContextCleanup *cleanup;
    181 public:
    182   CrashRecoveryContextCleanupRegistrar(T *x)
    183     : cleanup(Cleanup::create(x)) {
    184     if (cleanup)
    185       cleanup->getContext()->registerCleanup(cleanup);
    186   }
    187 
    188   ~CrashRecoveryContextCleanupRegistrar() {
    189     unregister();
    190   }
    191 
    192   void unregister() {
    193     if (cleanup && !cleanup->cleanupFired)
    194       cleanup->getContext()->unregisterCleanup(cleanup);
    195     cleanup = 0;
    196   }
    197 };
    198 }
    199 
    200 #endif
    201