G4Backtrace.hh

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//
// ********************************************************************
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// *                                                                  *
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// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
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// * institutes,nor the agencies providing financial support for this *
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// * use.  Please see the license in the file  LICENSE  and URL above *
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// * technical work of the GEANT4 collaboration.                      *
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// ********************************************************************
//
// G4Backtrace
//
// Description:
//
//  Prints backtraces after signals are caught. Available on Unix.
//
// Usage:
//  A standard set of signals are enabled by default:
//
//     SIGQUIT, SIGILL, SIGABRT, SIGKILL, SIGBUS, SIGSEGV
//
//  These should not interfere with debuggers and/or G4FPEDetection.
//  In order to turn off handling for one or more signals, one can do:
//
//    G4Backtrace::DefaultSignals() = std::set<int>{};
//    G4Backtrace::DefaultSignals() = std::set<int>{ SIGSEGV };
//
//  and so on, *before* creating the run-manager. After the run-manager
//  has been created, one should disable the signals:
//
//    G4Backtrace::Disable(G4Backtrace::DefaultSignals());
//
//  Additionally, at runtime, the environment variable "G4BACKTRACE" can
//  be set to select a specific set of signals or none, e.g. in bash:
//
//    export G4BACKTRACE="SIGQUIT,SIGSEGV"
//    export G4BACKTRACE="none"
//
//  The environment variable is case-insensitive and can use any of the
//  following delimiters: space, comma, semi-colon, colon
//
// Author: J.Madsen, 19 October 2020
// --------------------------------------------------------------------
 
#ifndef G4Backtrace_hh
#define G4Backtrace_hh 1
 
#include "G4Types.hh"
#include "G4String.hh"
#include "G4Threading.hh"
 
#if defined(__APPLE__) || defined(__MACH__)
#  if !defined(G4MACOS)
#    define G4MACOS
#  endif
#  if !defined(G4UNIX)
#    define G4UNIX
#  endif
#elif defined(__linux__) || defined(__linux) || defined(linux) ||              \
  defined(__gnu_linux__)
#  if !defined(G4LINUX)
#    define G4LINUX
#  endif
#  if !defined(G4UNIX)
#    define G4UNIX
#  endif
#elif defined(__unix__) || defined(__unix) || defined(unix)
#  if !defined(G4UNIX)
#    define G4UNIX
#  endif
#endif
 
#if defined(G4UNIX) && !defined(WIN32)
#  include <cxxabi.h>
#  include <execinfo.h>
#  include <unistd.h>
#endif
 
#if defined(G4LINUX)
#  include <features.h>
#endif
 
#include <cfenv>
#include <csignal>
#include <type_traits>
 
template <typename FuncT, typename... ArgTypes>
using G4ResultOf_t = std::invoke_result_t<FuncT, ArgTypes...>;
 
// compatible OS and compiler
#if defined(G4UNIX) &&                                                         \
  (defined(__GNUC__) || defined(__clang__) || defined(_INTEL_COMPILER))
#  if !defined(G4SIGNAL_AVAILABLE)
#    define G4SIGNAL_AVAILABLE
#  endif
#  if !defined(G4DEMANGLE_AVAILABLE)
#    define G4DEMANGLE_AVAILABLE
#  endif
#endif
 
#if !defined(G4PSIGINFO_AVAILABLE)
#  if _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
#    define G4PSIGINFO_AVAILABLE 1
#  else
#    define G4PSIGINFO_AVAILABLE 0
#  endif
#endif
 
//----------------------------------------------------------------------------//
 
inline G4String G4Demangle(const char* _str)
{
#if defined(G4DEMANGLE_AVAILABLE)
  // demangling a string when delimiting
  G4int _status = 0;
  char* _ret  = ::abi::__cxa_demangle(_str, nullptr, nullptr, &_status);
  if((_ret != nullptr) && _status == 0)
    return G4String(const_cast<const char*>(_ret));
  return _str;
#else
  return _str;
#endif
}
 
//----------------------------------------------------------------------------//
 
inline G4String G4Demangle(const G4String& _str)
{
  return G4Demangle(_str.c_str());
}
 
//----------------------------------------------------------------------------//
 
template <typename Tp>
inline G4String G4Demangle()
{
  return G4Demangle(typeid(Tp).name());
}
 
//----------------------------------------------------------------------------//
//
//      ONLY IF G4SIGNAL_AVAILABLE
//
//----------------------------------------------------------------------------//
//
#if defined(G4SIGNAL_AVAILABLE)
//
//  these are not in the original POSIX.1-1990 standard so we are defining
//  them in case the OS hasn't
//  POSIX-1.2001
#  ifndef SIGTRAP
#    define SIGTRAP 5
#  endif
//  not specified in POSIX.1-2001, but nevertheless appears on most other
//  UNIX systems, where its default action is typically to terminate the
//  process with a core dump.
#  ifndef SIGEMT
#    define SIGEMT 7
#  endif
//  POSIX-1.2001
#  ifndef SIGURG
#    define SIGURG 16
#  endif
//  POSIX-1.2001
#  ifndef SIGXCPU
#    define SIGXCPU 24
#  endif
//  POSIX-1.2001
#  ifndef SIGXFSZ
#    define SIGXFSZ 25
#  endif
//  POSIX-1.2001
#  ifndef SIGVTALRM
#    define SIGVTALRM 26
#  endif
//  POSIX-1.2001
#  ifndef SIGPROF
#    define SIGPROF 27
#  endif
//  POSIX-1.2001
#  ifndef SIGINFO
#    define SIGINFO 29
#  endif
 
//----------------------------------------------------------------------------//
 
#  include <algorithm>
#  include <array>
#  include <cstdlib>
#  include <cstdio>
#  include <functional>
#  include <iomanip>
#  include <iostream>
#  include <map>
#  include <regex>
#  include <set>
#  include <sstream>
#  include <string>
#  include <tuple>
#  include <vector>
 
//----------------------------------------------------------------------------//
 
class G4Backtrace
{
 public:
  using sigaction_t   = struct sigaction;
  using exit_action_t = std::function<void(G4int)>;
  using frame_func_t  = std::function<G4String(const char*)>;
  using signal_set_t  = std::set<G4int>;
 
 public:
  struct actions
  {
    using id_entry_t = std::tuple<std::string, G4int, std::string>;
    using id_list_t  = std::vector<id_entry_t>;
 
    std::map<G4int, G4bool> is_active           = {};
    std::map<G4int, sigaction_t> current      = {};
    std::map<G4int, sigaction_t> previous     = {};
    std::vector<exit_action_t> exit_actions = {};
    const id_list_t identifiers             = {
      id_entry_t("SIGHUP", SIGHUP, "terminal line hangup"),
      id_entry_t("SIGINT", SIGINT, "interrupt program"),
      id_entry_t("SIGQUIT", SIGQUIT, "quit program"),
      id_entry_t("SIGILL", SIGILL, "illegal instruction"),
      id_entry_t("SIGTRAP", SIGTRAP, "trace trap"),
      id_entry_t("SIGABRT", SIGABRT, "abort program (formerly SIGIOT)"),
      id_entry_t("SIGEMT", SIGEMT, "emulate instruction executed"),
      id_entry_t("SIGFPE", SIGFPE, "floating-point exception"),
      id_entry_t("SIGKILL", SIGKILL, "kill program"),
      id_entry_t("SIGBUS", SIGBUS, "bus error"),
      id_entry_t("SIGSEGV", SIGSEGV, "segmentation violation"),
      id_entry_t("SIGSYS", SIGSYS, "non-existent system call invoked"),
      id_entry_t("SIGPIPE", SIGPIPE, "write on a pipe with no reader"),
      id_entry_t("SIGALRM", SIGALRM, "real-time timer expired"),
      id_entry_t("SIGTERM", SIGTERM, "software termination signal"),
      id_entry_t("SIGURG", SIGURG, "urgent condition present on socket"),
      id_entry_t("SIGSTOP", SIGSTOP, "stop (cannot be caught or ignored)"),
      id_entry_t("SIGTSTP", SIGTSTP, "stop signal generated from keyboard"),
      id_entry_t("SIGCONT", SIGCONT, "continue after stop"),
      id_entry_t("SIGCHLD", SIGCHLD, "child status has changed"),
      id_entry_t("SIGTTIN", SIGTTIN,
                 "background read attempted from control terminal"),
      id_entry_t("SIGTTOU", SIGTTOU,
                 "background write attempted to control terminal"),
      id_entry_t("SIGIO ", SIGIO, "I/O is possible on a descriptor"),
      id_entry_t("SIGXCPU", SIGXCPU, "cpu time limit exceeded"),
      id_entry_t("SIGXFSZ", SIGXFSZ, "file size limit exceeded"),
      id_entry_t("SIGVTALRM", SIGVTALRM, "virtual time alarm"),
      id_entry_t("SIGPROF", SIGPROF, "profiling timer alarm"),
      id_entry_t("SIGWINCH", SIGWINCH, "Window size change"),
      id_entry_t("SIGINFO", SIGINFO, "status request from keyboard"),
      id_entry_t("SIGUSR1", SIGUSR1, "User defined signal 1"),
      id_entry_t("SIGUSR2", SIGUSR2, "User defined signal 2")
    };
  };
 
 public:
  // a functor called for each frame in the backtrace
  static frame_func_t& FrameFunctor();
  // default set of signals
  static signal_set_t& DefaultSignals();
  // the signal handler
  static void Handler(G4int sig, siginfo_t* sinfo, void* context);
  // information message about the signal, performs exit-actions
  // and prints back-trace
  static void Message(G4int sig, siginfo_t* sinfo, std::ostream&);
  // calls user-provided functions after signal is caught but before abort
  static void ExitAction(G4int sig);
  // enable signals via a string (which is tokenized)
  static G4int Enable(const std::string&);
  // enable signals via set of integers, anything less than zero is ignored
  static G4int Enable(const signal_set_t& _signals = DefaultSignals());
  // disable signals
  static G4int Disable(signal_set_t _signals = {});
  // gets the numeric value for a signal name
  static G4int GetSignal(const std::string&);
  // provides a description of the signal
  static std::string Description(G4int sig);
 
  // adds an exit action
  template <typename FuncT>
  static void AddExitAction(FuncT&& func);
 
  // gets a backtrace of "Depth" frames. The offset parameter is used
  // to ignore initial frames (such as this function). A callback
  // can be provided to inspect and/or tweak the frame string
  template <std::size_t Depth, std::size_t Offset = 0, typename FuncT = frame_func_t>
  static std::array<G4ResultOf_t<FuncT, const char*>, Depth> GetMangled(
    FuncT&& func = FrameFunctor());
 
  // gets a demangled backtrace of "Depth" frames. The offset parameter is
  // used to ignore initial frames (such as this function). A callback
  // can be provided to inspect and/or tweak the frame string
  template <std::size_t Depth, std::size_t Offset = 0, typename FuncT = frame_func_t>
  static std::array<G4ResultOf_t<FuncT, const char*>, Depth> GetDemangled(
    FuncT&& func = FrameFunctor());
 
 private:
  static actions& GetData()
  {
    static auto _instance = actions{};
    return _instance;
  }
};
 
//----------------------------------------------------------------------------//
 
// a functor called for each frame in the backtrace
inline G4Backtrace::frame_func_t& G4Backtrace::FrameFunctor()
{
  static frame_func_t _instance = [](const char* inp) { return G4String(inp); };
  return _instance;
}
 
//----------------------------------------------------------------------------//
 
// default set of signals
inline G4Backtrace::signal_set_t& G4Backtrace::DefaultSignals()
{
  static signal_set_t _instance = { SIGQUIT, SIGILL, SIGABRT,
                                    SIGKILL, SIGBUS, SIGSEGV };
  return _instance;
}
 
//----------------------------------------------------------------------------//
 
template <typename FuncT>
inline void G4Backtrace::AddExitAction(FuncT&& func)
{
  GetData().exit_actions.emplace_back(std::forward<FuncT>(func));
}
 
//----------------------------------------------------------------------------//
 
inline void G4Backtrace::ExitAction(G4int sig)
{
  for(auto& itr : GetData().exit_actions)
    itr(sig);
}
 
//----------------------------------------------------------------------------//
 
template <std::size_t Depth, std::size_t Offset, typename FuncT>
inline std::array<G4ResultOf_t<FuncT, const char*>, Depth>
G4Backtrace::GetMangled(FuncT&& func)
{
  static_assert((Depth - Offset) >= 1, "Error Depth - Offset should be >= 1");
 
  using type = G4ResultOf_t<FuncT, const char*>;
  // destination
  std::array<type, Depth> btrace;
  btrace.fill((std::is_pointer<type>::value) ? nullptr : type{});
 
  // plus one for this stack-frame
  std::array<void*, Depth + Offset> buffer;
  // size of returned buffer
  auto sz = backtrace(buffer.data(), Depth + Offset);
  // size of relevant data
  auto n = sz - Offset;
 
  // skip ahead (Offset + 1) stack frames
  char** bsym = backtrace_symbols(buffer.data() + Offset, (G4int)n);
 
  // report errors
  if(bsym == nullptr)
    perror("backtrace_symbols");
  else
  {
    for(decltype(n) i = 0; i < n; ++i)
      btrace[i] = func(bsym[i]);
    free(bsym);
  }
  return btrace;
}
 
//----------------------------------------------------------------------------//
 
template <std::size_t Depth, std::size_t Offset, typename FuncT>
inline std::array<G4ResultOf_t<FuncT, const char*>, Depth>
G4Backtrace::GetDemangled(FuncT&& func)
{
  auto demangle_bt = [&](const char* cstr) {
    auto _trim = [](std::string& _sub, std::size_t& _len) {
      std::size_t _pos = 0;
      while((_pos = _sub.find_first_of(' ')) == 0)
      {
        _sub = _sub.erase(_pos, 1);
        --_len;
      }
      while((_pos = _sub.find_last_of(' ')) == _sub.length() - 1)
      {
        _sub = _sub.substr(0, _sub.length() - 1);
        --_len;
      }
      return _sub;
    };
 
    auto str = G4Demangle(std::string(cstr));
    auto beg = str.find('(');
    if(beg == std::string::npos)
    {
      beg = str.find("_Z");
      if(beg != std::string::npos)
        beg -= 1;
    }
    auto end = str.find('+', beg);
    if(beg != std::string::npos && end != std::string::npos)
    {
      auto len = end - (beg + 1);
      auto sub = str.substr(beg + 1, len);
      auto dem = G4Demangle(_trim(sub, len));
      str      = str.replace(beg + 1, len, dem);
    }
    else if(beg != std::string::npos)
    {
      auto len = str.length() - (beg + 1);
      auto sub = str.substr(beg + 1, len);
      auto dem = G4Demangle(_trim(sub, len));
      str      = str.replace(beg + 1, len, dem);
    }
    else if(end != std::string::npos)
    {
      auto len = end;
      auto sub = str.substr(beg, len);
      auto dem = G4Demangle(_trim(sub, len));
      str      = str.replace(beg, len, dem);
    }
    return func(str.c_str());
  };
  return GetMangled<Depth, Offset>(demangle_bt);
}
 
//----------------------------------------------------------------------------//
 
inline void G4Backtrace::Message(G4int sig, siginfo_t* sinfo, std::ostream& os)
{
  // try to avoid as many dynamic allocations as possible here to avoid
  // overflowing the signal stack
 
  // ignore future signals of this type
  signal(sig, SIG_IGN);
 
  os << "\n### CAUGHT SIGNAL: " << sig << " ### ";
  if(sinfo != nullptr)
    os << "address: " << sinfo->si_addr << ", ";
  os << Description(sig) << ". ";
 
  if(sig == SIGSEGV)
  {
    if(sinfo != nullptr)
    {
      switch(sinfo->si_code)
      {
        case SEGV_MAPERR:
          os << "Address not mapped to object.";
          break;
        case SEGV_ACCERR:
          os << "Invalid permissions for mapped object.";
          break;
        default:
          os << "Unknown segmentation fault error: " << sinfo->si_code << ".";
          break;
      }
    }
    else
    {
      os << "Segmentation fault (unknown).";
    }
  }
  else if(sig == SIGFPE)
  {
    if(sinfo != nullptr)
    {
      switch(sinfo->si_code)
      {
        case FE_DIVBYZERO:
          os << "Floating point divide by zero.";
          break;
        case FE_OVERFLOW:
          os << "Floating point overflow.";
          break;
        case FE_UNDERFLOW:
          os << "Floating point underflow.";
          break;
        case FE_INEXACT:
          os << "Floating point inexact result.";
          break;
        case FE_INVALID:
          os << "Floating point invalid operation.";
          break;
        default:
          os << "Unknown floating point exception error: " << sinfo->si_code
             << ".";
          break;
      }
    }
    else
    {
      os << "Unknown floating point exception";
      if(sinfo != nullptr)
        os << ": " << sinfo->si_code;
      os << ". ";
    }
  }
 
  os << '\n';
 
  auto bt = GetMangled<256, 3>([](const char* _s) { return _s; });
  char prefix[64];
  snprintf(prefix, 64, "[PID=%i, TID=%i]", (G4int) getpid(),
           (G4int) G4Threading::G4GetThreadId());
  std::size_t sz = 0;
  for(auto& itr : bt)
  {
    if(itr == nullptr)
      break;
    if(strlen(itr) == 0)
      break;
    ++sz;
  }
  os << "\nBacktrace:\n";
  auto _w = std::log10(sz) + 1;
  for(std::size_t i = 0; i < sz; ++i)
  {
    os << prefix << "[" << std::setw(_w) << std::right << i << '/'
       << std::setw(_w) << std::right << sz << "]> " << std::left << bt.at(i)
       << '\n';
  }
  os << std::flush;
 
  // exit action could cause more signals to be raise so make sure this is done
  // after the message has been printed
  try
  {
    ExitAction(sig);
  } catch(std::exception& e)
  {
    std::cerr << "ExitAction(" << sig << ") threw an exception" << std::endl;
    std::cerr << e.what() << std::endl;
  }
}
 
//----------------------------------------------------------------------------//
 
inline void G4Backtrace::Handler(G4int sig, siginfo_t* sinfo, void*)
{
  Message(sig, sinfo, std::cerr);
 
  char msg[1024];
  snprintf(msg, 1024, "%s", "\n");
 
  if((sinfo != nullptr) && G4PSIGINFO_AVAILABLE > 0)
  {
#  if G4PSIGINFO_AVAILABLE > 0
    psiginfo(sinfo, msg);
    fflush(stdout);
    fflush(stderr);
#  endif
  }
  else
  {
    std::cerr << msg << std::flush;
  }
 
  // ignore any termination signals
  signal(SIGKILL, SIG_IGN);
  signal(SIGTERM, SIG_IGN);
  signal(SIGABRT, SIG_IGN);
  abort();
}
 
//----------------------------------------------------------------------------//
 
inline G4int G4Backtrace::Enable(const signal_set_t& _signals)
{
  static G4bool _first = true;
  if(_first)
  {
    std::string _msg = "!!! G4Backtrace is activated !!!";
    std::stringstream _filler;
    std::stringstream _spacer;
    _filler.fill('#');
    _filler << std::setw((G4int)_msg.length()) << "";
    _spacer << std::setw(10) << "";
    std::cout << "\n\n"
              << _spacer.str() << _filler.str() << "\n"
              << _spacer.str() << _msg << "\n"
              << _spacer.str() << _filler.str() << "\n\n"
              << std::flush;
  }
  _first  = false;
  G4int cnt = 0;
  for(auto& itr : _signals)
  {
    if(itr < 0)
      continue;
    if(GetData().is_active[itr])
      continue;
    ++cnt;
    sigfillset(&(GetData().current[itr].sa_mask));
    sigdelset(&(GetData().current[itr].sa_mask), itr);
    GetData().current[itr].sa_sigaction = &Handler;
    GetData().current[itr].sa_flags     = SA_SIGINFO;
    sigaction(itr, &(GetData().current[itr]), &(GetData().previous[itr]));
  }
  return cnt;
}
 
//----------------------------------------------------------------------------//
 
inline G4int G4Backtrace::Enable(const std::string& _signals)
{
  if(_signals.empty())
    return 0;
 
  auto _add_signal = [](std::string sig, signal_set_t& _targ) {
    if(!sig.empty())
    {
      for(auto& itr : sig)
        itr = (char)std::toupper(itr);
      _targ.insert(G4Backtrace::GetSignal(sig));
    }
  };
 
  const std::regex wsp_re("[ ,;:\t\n]+");
  auto _maxid  = GetData().identifiers.size();
  auto _result = std::vector<std::string>(_maxid, "");
  std::copy(
    std::sregex_token_iterator(_signals.begin(), _signals.end(), wsp_re, -1),
    std::sregex_token_iterator(), _result.begin());
  signal_set_t _sigset{};
  for(auto& itr : _result)
    _add_signal(itr, _sigset);
  return Enable(_sigset);
}
 
//----------------------------------------------------------------------------//
 
inline G4int G4Backtrace::Disable(signal_set_t _signals)
{
  if(_signals.empty())
  {
    for(auto& itr : GetData().is_active)
      _signals.insert(itr.first);
  }
 
  G4int cnt = 0;
  for(auto& itr : _signals)
  {
    if(itr < 0)
      continue;
    if(!GetData().is_active[itr])
      continue;
    ++cnt;
    sigaction(itr, &(GetData().previous[itr]), nullptr);
    GetData().current.erase(itr);
    GetData().is_active[itr] = false;
  }
  return cnt;
}
 
//----------------------------------------------------------------------------//
 
inline G4int G4Backtrace::GetSignal(const std::string& sid)
{
  for(auto&& itr : GetData().identifiers)
  {
    if(std::get<0>(itr) == sid)
      return std::get<1>(itr);
  }
  return -1;
}
 
//----------------------------------------------------------------------------//
 
inline std::string G4Backtrace::Description(G4int sig)
{
  for(auto&& itr : GetData().identifiers)
  {
    if(std::get<1>(itr) == sig)
    {
      std::stringstream ss;
      ss << " signal = " << std::setw(8) << std::get<0>(itr)
         << ", value = " << std::setw(4) << std::get<1>(itr)
         << ", description = " << std::get<2>(itr);
      return ss.str();
    }
  }
  std::stringstream ss;
  ss << " signal = " << std::setw(8) << "unknown"
     << ", value = " << std::setw(4) << sig;
  return ss.str();
}
 
//----------------------------------------------------------------------------//
 
#else
 
#  include <array>
#  include <functional>
#  include <map>
#  include <set>
#  include <string>
#  include <tuple>
#  include <vector>
 
// dummy implementation
class G4Backtrace
{
 public:
  struct fake_siginfo
  {};
  struct fake_sigaction
  {};
 
  using siginfo_t = fake_siginfo;
  using sigaction_t = fake_sigaction;
  using exit_action_t = std::function<void(G4int)>;
  using frame_func_t = std::function<G4String(const char*)>;
  using signal_set_t = std::set<G4int>;
 
 public:
  struct actions
  {
    using id_entry_t = std::tuple<std::string, G4int, std::string>;
    using id_list_t = std::vector<id_entry_t>;
 
    std::map<G4int, G4bool> is_active = {};
    std::map<G4int, sigaction_t> current = {};
    std::map<G4int, sigaction_t> previous = {};
    std::vector<exit_action_t> exit_actions = {};
    const id_list_t identifiers = {};
  };
 
 public:
  static void Handler(G4int, siginfo_t*, void*) {}
  static void Message(G4int, siginfo_t*, std::ostream&) {}
  static void ExitAction(G4int) {}
  static G4int Enable(const std::string&) { return 0; }
  static G4int Enable(const signal_set_t& = DefaultSignals()) { return 0; }
  static G4int Disable(signal_set_t = {}) { return 0; }
  static G4int GetSignal(const std::string&) { return -1; }
  static std::string Description(G4int) { return std::string{}; }
 
  template <typename FuncT>
  static void AddExitAction(FuncT&&)
  {}
 
  template <std::size_t Depth, std::size_t Offset = 0, typename FuncT = frame_func_t>
  static std::array<G4ResultOf_t<FuncT, const char*>, Depth> GetMangled(
    FuncT&& func = FrameFunctor())
  {
    using type = G4ResultOf_t<FuncT, const char*>;
    auto ret = std::array<type, Depth>{};
    ret.fill(func(""));
    return ret;
  }
 
  template <std::size_t Depth, std::size_t Offset = 0, typename FuncT = frame_func_t>
  static std::array<G4ResultOf_t<FuncT, const char*>, Depth> GetDemangled(
    FuncT&& func = FrameFunctor())
  {
    using type = G4ResultOf_t<FuncT, const char*>;
    auto ret = std::array<type, Depth>{};
    ret.fill(func(""));
    return ret;
  }
 
  // a functor called for each frame in the backtrace
  static frame_func_t& FrameFunctor()
  {
    static frame_func_t _instance = [](const char* _s) { return G4String(_s); };
    return _instance;
  }
 
  // default set of signals
  static signal_set_t& DefaultSignals()
  {
    static signal_set_t _instance = {};
    return _instance;
  }
 
  static actions& GetData()
  {
    static auto _instance = actions{};
    return _instance;
  }
};
 
//----------------------------------------------------------------------------//
 
#endif  // G4SIGNAL_AVAILABLE
#endif  // G4Backtrace_hh