InitRootHandlers.cc

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#include "FWCore/ServiceRegistry/interface/ServiceMaker.h"

#include "FWCore/Utilities/interface/RootHandlers.h"

#include "FWCore/ServiceRegistry/interface/ActivityRegistry.h"
#include "FWCore/ServiceRegistry/interface/SystemBounds.h"
#include "DataFormats/Common/interface/RefCoreStreamer.h"
#include "DataFormats/Provenance/interface/ModuleDescription.h"
#include "FWCore/MessageLogger/interface/ELseverityLevel.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/PluginManager/interface/PluginCapabilities.h"
#include "FWCore/ParameterSet/interface/ConfigurationDescriptions.h"
#include "FWCore/ParameterSet/interface/ParameterSetDescription.h"
#include "FWCore/Utilities/interface/EDMException.h"
#include "FWCore/Utilities/interface/TypeWithDict.h"
#include "FWCore/Utilities/interface/UnixSignalHandlers.h"
#include "FWCore/ServiceRegistry/interface/CurrentModuleOnThread.h"
#include "FWCore/ServiceRegistry/interface/ModuleCallingContext.h"

#include "tbb/task.h"
#include "tbb/task_scheduler_observer.h"
#include "tbb/concurrent_unordered_set.h"
#include <thread>
#include <sys/wait.h>
#include <sstream>
#include <cstring>
#include <poll.h>
#include <atomic>
#include <algorithm>
#include <vector>
#include <string>
#include <array>

// WORKAROUND: At CERN, execv is replaced with a non-async-signal safe
// version.  This can break our stack trace printer.  Avoid this by
// invoking the syscall directly.
#ifdef __linux__
#include <syscall.h>
#endif

#include "TROOT.h"
#include "TError.h"
#include "TFile.h"
#include "TInterpreter.h"
#include "TH1.h"
#include "TSystem.h"
#include "TUnixSystem.h"
#include "TTree.h"
#include "TVirtualStreamerInfo.h"

#include "TClassTable.h"

#include <memory>

namespace {
  // size of static buffer allocated for listing module names following a
  // stacktrace abort
  constexpr std::size_t moduleBufferSize = 128;
}

namespace edm {
  class ConfigurationDescriptions;
  class ParameterSet;
  class ActivityRegistry;
  
  namespace service {
    class InitRootHandlers : public RootHandlers {
      
      friend int cmssw_stacktrace(void *);
      
    public:
      class ThreadTracker : public tbb::task_scheduler_observer {
      public:
        typedef tbb::concurrent_unordered_set<pthread_t> Container_type;

        ThreadTracker() : tbb::task_scheduler_observer() {
          observe(true);
        }
        void on_scheduler_entry(bool) override {
          // ensure thread local has been allocated; not necessary on Linux with
          // the current cmsRun linkage, but could be an issue if the platform
          // or linkage leads to "lazy" allocation of the thread local.  By
          // referencing it here we make sure it has been allocated and can be
          // accessed safely from our signal handler.
          edm::CurrentModuleOnThread::getCurrentModuleOnThread();
          threadIDs_.insert(pthread_self());
        }
        const Container_type& IDs() { return threadIDs_; }
      
      private:
        Container_type threadIDs_;
      };

      explicit InitRootHandlers(ParameterSet const& pset, ActivityRegistry& iReg);
      ~InitRootHandlers() override;
      
      static void fillDescriptions(ConfigurationDescriptions& descriptions);
      static void stacktraceFromThread();
      static const ThreadTracker::Container_type& threadIDs() { return threadTracker_.IDs(); }
      static int stackTracePause() { return stackTracePause_; }

      static std::vector<std::array<char,moduleBufferSize>> moduleListBuffers_;
      static std::atomic<std::size_t> nextModule_, doneModules_;
    private:
      static char *const *getPstackArgv();
      void enableWarnings_() override;
      void ignoreWarnings_(edm::RootHandlers::SeverityLevel level) override;
      void willBeUsingThreads() override;

      void cachePidInfo();
      static void stacktraceHelperThread();

      static const int pidStringLength_ = 200;
      static char pidString_[pidStringLength_];
      static char * const pstackArgv_[];
      static int parentToChild_[2];
      static int childToParent_[2];
      static std::unique_ptr<std::thread> helperThread_;
      static ThreadTracker threadTracker_;
      static int stackTracePause_;

      bool unloadSigHandler_;
      bool resetErrHandler_;
      bool loadAllDictionaries_;
      bool autoLibraryLoader_;
      std::shared_ptr<const void> sigBusHandler_;
      std::shared_ptr<const void> sigSegvHandler_;
      std::shared_ptr<const void> sigIllHandler_;
      std::shared_ptr<const void> sigTermHandler_;
      std::shared_ptr<const void> sigAbrtHandler_;
    };
    
    inline
    bool isProcessWideService(InitRootHandlers const*) {
      return true;
    }
    
  }  // end of namespace service
}  // end of namespace edm

namespace edm {
  namespace service {
    int cmssw_stacktrace(void *);
  }
}

namespace {
  thread_local edm::RootHandlers::SeverityLevel s_ignoreWarnings = edm::RootHandlers::SeverityLevel::kInfo;

  bool s_ignoreEverything = false;

  template<std::size_t SIZE>
  bool find_if_string(const std::string& search, const std::array<const char* const,SIZE>& substrs){
    return (std::find_if(substrs.begin(), substrs.end(), [&search](const char* const s) -> bool { return (search.find(s) != std::string::npos); }) != substrs.end());
  }

  constexpr std::array<const char* const,8> in_message{{
    "no dictionary for class",
    "already in TClassTable",
    "matrix not positive definite",
    "not a TStreamerInfo object",
    "Problems declaring payload",
    "Announced number of args different from the real number of argument passed", // Always printed if gDebug>0 - regardless of whether warning message is real.
    "nbins is <=0 - set to nbins = 1",
    "nbinsy is <=0 - set to nbinsy = 1"
  }};

  constexpr std::array<const char* const,6> in_location{{
    "Fit",
    "TDecompChol::Solve",
    "THistPainter::PaintInit",
    "TUnixSystem::SetDisplay",
    "TGClient::GetFontByName",
    "Inverter::Dinv"
  }};

  constexpr std::array<const char* const,3> in_message_print{{
    "number of iterations was insufficient",
    "bad integrand behavior",
    "integral is divergent, or slowly convergent"
  }};

  void RootErrorHandlerImpl(int level, char const* location, char const* message) {

  bool die = false;

  // Translate ROOT severity level to MessageLogger severity level

    edm::RootHandlers::SeverityLevel el_severity = edm::RootHandlers::SeverityLevel::kInfo;

    if (level >= kFatal) {
      el_severity = edm::RootHandlers::SeverityLevel::kFatal;
    } else if (level >= kSysError) {
      el_severity = edm::RootHandlers::SeverityLevel::kSysError;
    } else if (level >= kError) {
      el_severity = edm::RootHandlers::SeverityLevel::kError;
    } else if (level >= kWarning) {
      el_severity = edm::RootHandlers::SeverityLevel::kWarning;
    }

    if (s_ignoreEverything || el_severity <= s_ignoreWarnings) {
      el_severity = edm::RootHandlers::SeverityLevel::kInfo;
    }

  // Adapt C-strings to std::strings
  // Arrange to report the error location as furnished by Root

    std::string el_location = "@SUB=?";
    if (location != nullptr) el_location = std::string("@SUB=")+std::string(location);

    std::string el_message  = "?";
    if (message != nullptr) el_message  = message;

  // Try to create a meaningful id string using knowledge of ROOT error messages
  //
  // id ==     "ROOT-ClassName" where ClassName is the affected class
  //      else "ROOT/ClassName" where ClassName is the error-declaring class
  //      else "ROOT"

    std::string el_identifier = "ROOT";

    std::string precursor("class ");
    size_t index1 = el_message.find(precursor);
    if (index1 != std::string::npos) {
      size_t index2 = index1 + precursor.length();
      size_t index3 = el_message.find_first_of(" :", index2);
      if (index3 != std::string::npos) {
        size_t substrlen = index3-index2;
        el_identifier += "-";
        el_identifier += el_message.substr(index2,substrlen);
      }
    } else {
      index1 = el_location.find("::");
      if (index1 != std::string::npos) {
        el_identifier += "/";
        el_identifier += el_location.substr(0, index1);
      }
    }

  // Intercept some messages and upgrade the severity

      if ((el_location.find("TBranchElement::Fill") != std::string::npos)
       && (el_message.find("fill branch") != std::string::npos)
       && (el_message.find("address") != std::string::npos)
       && (el_message.find("not set") != std::string::npos)) {
        el_severity = edm::RootHandlers::SeverityLevel::kFatal;
      }

      if ((el_message.find("Tree branches") != std::string::npos)
       && (el_message.find("different numbers of entries") != std::string::npos)) {
        el_severity = edm::RootHandlers::SeverityLevel::kFatal;
      }


  // Intercept some messages and downgrade the severity

      if (find_if_string(el_message,in_message) ||
          find_if_string(el_location,in_location) ||
          (level < kError and (el_location.find("CINTTypedefBuilder::Setup")!= std::string::npos) and (el_message.find("possible entries are in use!") != std::string::npos)))
      {
        el_severity = edm::RootHandlers::SeverityLevel::kInfo;
      }

      // These are a special case because we do not want them to
      // be fatal, but we do want an error to print.
      bool alreadyPrinted = false;
      if (find_if_string(el_message,in_message_print))
      {
        el_severity = edm::RootHandlers::SeverityLevel::kInfo;
        edm::LogError("Root_Error") << el_location << el_message;
        alreadyPrinted = true;
      }

    if (el_severity == edm::RootHandlers::SeverityLevel::kInfo) {
      // Don't throw if the message is just informational.
      die = false;
    } else {
      die = true;
    }

  // Feed the message to the MessageLogger and let it choose to suppress or not.

  // Root has declared a fatal error.  Throw an EDMException unless the
  // message corresponds to a pending signal. In that case, do not throw
  // but let the OS deal with the signal in the usual way.
    if (die && (el_location != std::string("@SUB=TUnixSystem::DispatchSignals"))) {
       std::ostringstream sstr;
       sstr << "Fatal Root Error: " << el_location << "\n" << el_message << '\n';
       edm::Exception except(edm::errors::FatalRootError, sstr.str());
       except.addAdditionalInfo(except.message());
       except.clearMessage();
       throw except;
     
    }

    // Typically, we get here only for informational messages,
    // but we leave the other code in just in case we change
    // the criteria for throwing.
    if (!alreadyPrinted) {
      if (el_severity == edm::RootHandlers::SeverityLevel::kFatal) {
        edm::LogError("Root_Fatal") << el_location << el_message;
      } else if (el_severity == edm::RootHandlers::SeverityLevel::kSysError) {
        edm::LogError("Root_Severe") << el_location << el_message;
      } else if (el_severity == edm::RootHandlers::SeverityLevel::kError) {
        edm::LogError("Root_Error") << el_location << el_message;
      } else if (el_severity == edm::RootHandlers::SeverityLevel::kWarning) {
        edm::LogWarning("Root_Warning") << el_location << el_message ;
      } else if (el_severity == edm::RootHandlers::SeverityLevel::kInfo) {
        edm::LogInfo("Root_Information") << el_location << el_message ;
      }
    }
  }

  void RootErrorHandler(int level, bool, char const* location, char const* message) {
    RootErrorHandlerImpl(level, location, message);
  }

  extern "C" {
    void set_default_signals() {
      signal(SIGILL, SIG_DFL);
      signal(SIGSEGV, SIG_DFL);
      signal(SIGBUS, SIG_DFL);
      signal(SIGTERM, SIG_DFL);
      signal(SIGABRT, SIG_DFL);
    }

    static int full_write(int fd, const char *text)
    {
      const char *buffer = text;
      size_t count = strlen(text);
      ssize_t written = 0;
      while (count)
      {
        written = write(fd, buffer, count);
        if (written == -1) 
        {
          if (errno == EINTR) {continue;}
          else {return -errno;}
        }
        count -= written;
        buffer += written;
      }
      return 0;
    }

    static int full_read(int fd, char *inbuf, size_t len, int timeout_s=-1)
    {
      char *buf = inbuf;
      size_t count = len;
      ssize_t complete = 0;
      std::chrono::time_point<std::chrono::steady_clock> end_time = std::chrono::steady_clock::now() + std::chrono::seconds(timeout_s);
      int flags;
      if (timeout_s < 0)
      {
        flags = O_NONBLOCK;  // Prevents us from trying to set / restore flags later.
      }
      else if ((-1 == (flags = fcntl(fd, F_GETFL))))
      {
        return -errno;
      }
      if ((flags & O_NONBLOCK) != O_NONBLOCK)
      {
        if (-1 == fcntl(fd, F_SETFL, flags | O_NONBLOCK))
        {
          return -errno;
        }
      }
      while (count)
      {
        if (timeout_s >= 0)
        {
          struct pollfd poll_info{fd, POLLIN, 0};
          int ms_remaining = std::chrono::duration_cast<std::chrono::milliseconds>(end_time-std::chrono::steady_clock::now()).count();
          if (ms_remaining > 0)
          {
            int rc = poll(&poll_info, 1, ms_remaining);
            if (rc <= 0)
            {
              if (rc < 0) {
                if (errno == EINTR || errno == EAGAIN) { continue; }
                rc = -errno;
              } else {
                rc = -ETIMEDOUT;
              }
              if ((flags & O_NONBLOCK) != O_NONBLOCK)
              {
                fcntl(fd, F_SETFL, flags);
              }
              return rc;
            }
          }
          else if (ms_remaining < 0)
          {
            if ((flags & O_NONBLOCK) != O_NONBLOCK)
            {
              fcntl(fd, F_SETFL, flags);
            }
            return -ETIMEDOUT;
          }
        }
        complete = read(fd, buf, count);
        if (complete == -1)
        {
          if (errno == EINTR) {continue;}
          else if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {continue;}
          else
          {
            int orig_errno = errno;
            if ((flags & O_NONBLOCK) != O_NONBLOCK)
            {
              fcntl(fd, F_SETFL, flags);
            }
            return -orig_errno;
          }
        }
        count -= complete;
        buf += complete;
      }
      if ((flags & O_NONBLOCK) != O_NONBLOCK) {
        fcntl(fd, F_SETFL, flags);
      }
      return 0;
    }

    static int full_cerr_write(const char *text)
    {
      return full_write(2, text);
    }

// these signals are only used inside the stacktrace signal handler,
// so common signals can be used.  They do have to be different, since
// we do not set SA_NODEFER, and RESUME must be a signal that will
// cause sleep() to return early.
#if defined(SIGRTMAX)
#define PAUSE_SIGNAL SIGRTMAX
#define RESUME_SIGNAL SIGRTMAX-1
#elif defined(SIGINFO) // macOS/BSD
#define PAUSE_SIGNAL SIGINFO
#define RESUME_SIGNAL SIGALRM
#endif

    // does nothing, here only to interrupt the sleep() in the pause handler
    void sig_resume_handler(int sig, siginfo_t*, void*) {}

    // pause a thread so that a (slow) stacktrace will capture the current state
    void sig_pause_for_stacktrace(int sig, siginfo_t*, void*) {
      using namespace edm::service;

#ifdef RESUME_SIGNAL
      sigset_t sigset;
      sigemptyset(&sigset);
      sigaddset(&sigset, RESUME_SIGNAL);
      pthread_sigmask(SIG_UNBLOCK, &sigset, nullptr);
#endif
      // sleep interrrupts on a handled delivery of the resume signal
      sleep(InitRootHandlers::stackTracePause());

      if (InitRootHandlers::doneModules_.is_lock_free() && InitRootHandlers::nextModule_.is_lock_free()) {
        auto i = InitRootHandlers::nextModule_++;
        if (i < InitRootHandlers::moduleListBuffers_.size()) {
          char* buff = InitRootHandlers::moduleListBuffers_[i].data();
        
          strlcpy(buff, "\nModule: ", moduleBufferSize);
          if (edm::CurrentModuleOnThread::getCurrentModuleOnThread() != nullptr) {
            strlcat(buff, edm::CurrentModuleOnThread::getCurrentModuleOnThread()->moduleDescription()->moduleName().c_str(), moduleBufferSize);
            strlcat(buff, ":", moduleBufferSize);
            strlcat(buff, edm::CurrentModuleOnThread::getCurrentModuleOnThread()->moduleDescription()->moduleLabel().c_str(), moduleBufferSize);
          } else {
            strlcat(buff, "none", moduleBufferSize);
          }
          ++edm::service::InitRootHandlers::doneModules_;
        }
      }
    }

    void sig_dostack_then_abort(int sig, siginfo_t*, void*) {
      using namespace edm::service;

      const auto& tids = InitRootHandlers::threadIDs();

      const auto self = pthread_self();
#ifdef PAUSE_SIGNAL
      if (InitRootHandlers::stackTracePause() > 0 && tids.size() > 1) {
        // install the "pause" handler
        struct sigaction act;
        act.sa_sigaction = sig_pause_for_stacktrace;
        act.sa_flags = 0;
        sigemptyset(&act.sa_mask);
        sigaction(PAUSE_SIGNAL, &act, nullptr);

        // unblock pause signal globally, resume is unblocked in the pause handler
        sigset_t pausesigset;
        sigemptyset(&pausesigset);
        sigaddset(&pausesigset, PAUSE_SIGNAL);
        sigprocmask(SIG_UNBLOCK, &pausesigset, nullptr);

        // send a pause signal to all CMSSW/TBB threads other than self
        for (auto id : tids) {
          if (self != id) {
            pthread_kill(id, PAUSE_SIGNAL);
          }
        }

#ifdef RESUME_SIGNAL
        // install the "resume" handler
        act.sa_sigaction = sig_resume_handler;
        sigaction(RESUME_SIGNAL, &act, nullptr);
#endif
      }
#endif

      const char* signalname = "unknown";
      switch (sig) {
        case SIGBUS:
        {
          signalname = "bus error";
          break;
        }
        case SIGSEGV:
        {
          signalname = "segmentation violation";
          break;
        }
        case SIGILL:
        {
          signalname = "illegal instruction";
          break;
        }
        case SIGTERM:
        {
          signalname = "external termination request";
          break;
        }
        case SIGABRT:
        {
          signalname = "abort signal";
          break;
        }
        default:
          break;
      }
      full_cerr_write("\n\nA fatal system signal has occurred: ");
      full_cerr_write(signalname);
      full_cerr_write("\nThe following is the call stack containing the origin of the signal.\n\n");

      edm::service::InitRootHandlers::stacktraceFromThread();
 
      // resume the signal handlers to store the current module; we are not guaranteed they
      // will have time to store their modules, so there is a race condition; this could be
      // avoided by storing the module information before sleeping, a change that may be
      // made when we're convinced accessing the thread-local current module is safe.
#ifdef RESUME_SIGNAL
      std::size_t notified = 0;
      if (InitRootHandlers::stackTracePause() > 0 && tids.size() > 1) {
        for (auto id : tids) {
          if (self != id) {
            if (pthread_kill(id, RESUME_SIGNAL) == 0) ++notified;
          }
        }
      }
#endif

      full_cerr_write("\nCurrent Modules:\n");

      // Checking tids.count(self) ensures that we only try to access the current module in
      // CMSSW/TBB threads.  Those threads access the thread-local current module at the same
      // time the thread is registered, so any lazy allocation will have been done at that
      // point.  Not necessary on Linux with the current cmsRun linkage, as the thread-local
      // is allocated at exec time, not lazily.
      if (tids.count(self) > 0) {
        char buff[moduleBufferSize] = "\nModule: ";
        if (edm::CurrentModuleOnThread::getCurrentModuleOnThread() != nullptr) {
          strlcat(buff, edm::CurrentModuleOnThread::getCurrentModuleOnThread()->moduleDescription()->moduleName().c_str(), moduleBufferSize);
          strlcat(buff, ":", moduleBufferSize);
          strlcat(buff, edm::CurrentModuleOnThread::getCurrentModuleOnThread()->moduleDescription()->moduleLabel().c_str(), moduleBufferSize);
        } else {
          strlcat(buff, "none", moduleBufferSize);
        }
        strlcat(buff, " (crashed)", moduleBufferSize);
        full_cerr_write(buff);
      } else {
        full_cerr_write("\nModule: non-CMSSW (crashed)");
      }

#ifdef PAUSE_SIGNAL
      // wait a short interval for the paused threads to resume and fill in their module
      // information, then print
      if (InitRootHandlers::doneModules_.is_lock_free()) {
        int spincount = 0;
        timespec t = { 0, 1000 };
        while (++spincount < 1000 && InitRootHandlers::doneModules_ < notified) { nanosleep(&t, nullptr); }
        for (std::size_t i = 0; i < InitRootHandlers::doneModules_; ++i) {
          full_cerr_write(InitRootHandlers::moduleListBuffers_[i].data());
        }
      }
#endif

      full_cerr_write("\n\nA fatal system signal has occurred: ");
      full_cerr_write(signalname);
      full_cerr_write("\n");

      // For these five known cases, re-raise the signal to get the correct
      // exit code.
      if ((sig == SIGILL) || (sig == SIGSEGV) || (sig == SIGBUS) || (sig == SIGTERM) || (sig == SIGABRT))
      {
        signal(sig, SIG_DFL);
        raise(sig);
      }
      else
      {
        set_default_signals();
        ::abort();
      }
    }
    
    void sig_abort(int sig, siginfo_t*, void*) {
      full_cerr_write("\n\nFatal system signal has occurred during exit\n");

      // re-raise the signal to get the correct exit code
      signal(sig, SIG_DFL);
      raise(sig);

      // shouldn't get here
      set_default_signals();
      ::sleep(10);
      ::abort();
    }
  }
}  // end of unnamed namespace

namespace edm {
  namespace service {

    /*
     * We've run into issues where GDB fails to print the thread which calls clone().
     * To avoid this problem, we have an alternate approach below where the signal handler
     * only reads/writes to a dedicated thread via pipes.  The helper thread does the clone()
     * invocation; we don't care if that thread is missing from the traceback in this case.
     */
    static void cmssw_stacktrace_fork();

    void InitRootHandlers::stacktraceHelperThread()
    {
      int toParent = childToParent_[1];
      int fromParent = parentToChild_[0];
      char buf[2]; buf[1] = '\0';

      while(true)
      {
        int result = full_read(fromParent, buf, 1);
        if (result < 0)
        {
          // To avoid a deadlock (this function is NOT re-entrant), reset signals
          // We never set them back to the CMSSW handler because we assume the parent
          // thread will abort for us.
          set_default_signals();
          close(toParent);
          full_cerr_write("\n\nTraceback helper thread failed to read from parent: ");
          full_cerr_write(strerror(-result));
          full_cerr_write("\n");
          ::abort();
        }
        if (buf[0] == '1')
        {
          set_default_signals();
          cmssw_stacktrace_fork();
          full_write(toParent, buf);
        }
        else if (buf[0] == '2')
        {
          // We have just finished forking.  Reload the file descriptors for thread
          // communication.
          close(toParent);
          close(fromParent);
          toParent = childToParent_[1];
          fromParent = parentToChild_[0];
        }
        else if (buf[0] == '3')
        {
          break;
        }
        else
        {
          set_default_signals();
          close(toParent);
          full_cerr_write("\n\nTraceback helper thread got unknown command from parent: ");
          full_cerr_write(buf);
          full_cerr_write("\n");
          ::abort();
        }
      }
    }

    void InitRootHandlers::stacktraceFromThread()
    {
      int result = full_write(parentToChild_[1], "1");
      if (result < 0)
      {
        full_cerr_write("\n\nAttempt to request stacktrace failed: ");
        full_cerr_write(strerror(-result));
        full_cerr_write("\n");
        return;
      }
      char buf[2]; buf[1] = '\0';
      if ((result = full_read(childToParent_[0], buf, 1, 5*60)) < 0)
      {
        full_cerr_write("\n\nWaiting for stacktrace completion failed: ");
        if (result == -ETIMEDOUT)
        {
          full_cerr_write("timed out waiting for GDB to complete.");
        }
        else
        {
          full_cerr_write(strerror(-result));
        }
        full_cerr_write("\n");
        return;
      }
    }

    void cmssw_stacktrace_fork()
    {
      char child_stack[4*1024];
      char *child_stack_ptr = child_stack + 4*1024;
        // On Linux, we currently use jemalloc.  This registers pthread_atfork handlers; these
        // handlers are *not* async-signal safe.  Hence, a deadlock is possible if we invoke
        // fork() from our signal handlers.  Accordingly, we use clone (not POSIX, but AS-safe)
        // as that is closer to the 'raw metal' syscall and avoids pthread_atfork handlers.
      int pid =
#ifdef __linux__
        clone(edm::service::cmssw_stacktrace, child_stack_ptr, CLONE_VM|CLONE_FS|SIGCHLD, nullptr);
#else
        fork();
      if (child_stack_ptr) {} // Suppress 'unused variable' warning on non-Linux
      if (pid == 0) { edm::service::cmssw_stacktrace(nullptr); }
#endif
      if (pid == -1)
      {
        full_cerr_write("(Attempt to perform stack dump failed.)\n");
      }
      else
      {
        int status;
        if (waitpid(pid, &status, 0) == -1)
        {
          full_cerr_write("(Failed to wait on stack dump output.)\n");
        }
        if (status)
        {
          full_cerr_write("(GDB stack trace failed unexpectedly)\n");
        }
      }
    }

    int cmssw_stacktrace(void * /*arg*/)
    {
      set_default_signals();

      char *const *argv = edm::service::InitRootHandlers::getPstackArgv();
      // NOTE: this is NOT async-signal-safe at CERN's lxplus service.
      // CERN uses LD_PRELOAD to replace execv with a function from libsnoopy which
      // calls dlsym.
#ifdef __linux__
      syscall(SYS_execve, "/bin/sh", argv, __environ);
#else
      execv("/bin/sh", argv);
#endif
      ::abort();
      return 1;
    }
    
    static char pstackName[] = "(CMSSW stack trace helper)";
    static char dashC[] = "-c";
    char InitRootHandlers::pidString_[InitRootHandlers::pidStringLength_] = {};
    char * const InitRootHandlers::pstackArgv_[] = {pstackName, dashC, InitRootHandlers::pidString_, nullptr};
    int InitRootHandlers::parentToChild_[2] = {-1, -1};
    int InitRootHandlers::childToParent_[2] = {-1, -1};
    std::unique_ptr<std::thread> InitRootHandlers::helperThread_;
    int InitRootHandlers::stackTracePause_ = 300;
    std::vector<std::array<char,moduleBufferSize>> InitRootHandlers::moduleListBuffers_;
    std::atomic<std::size_t> InitRootHandlers::nextModule_(0), InitRootHandlers::doneModules_(0);
    InitRootHandlers::ThreadTracker InitRootHandlers::threadTracker_;
    

    InitRootHandlers::InitRootHandlers (ParameterSet const& pset, ActivityRegistry& iReg)
      : RootHandlers(),
        unloadSigHandler_(pset.getUntrackedParameter<bool> ("UnloadRootSigHandler")),
        resetErrHandler_(pset.getUntrackedParameter<bool> ("ResetRootErrHandler")),
        loadAllDictionaries_(pset.getUntrackedParameter<bool>("LoadAllDictionaries")),
        autoLibraryLoader_(loadAllDictionaries_ or pset.getUntrackedParameter<bool> ("AutoLibraryLoader"))
    {
      stackTracePause_ = pset.getUntrackedParameter<int> ("StackTracePauseTime");
      
      if(unloadSigHandler_) {
      // Deactivate all the Root signal handlers and restore the system defaults
        gSystem->ResetSignal(kSigChild);
        gSystem->ResetSignal(kSigBus);
        gSystem->ResetSignal(kSigSegmentationViolation);
        gSystem->ResetSignal(kSigIllegalInstruction);
        gSystem->ResetSignal(kSigSystem);
        gSystem->ResetSignal(kSigPipe);
        gSystem->ResetSignal(kSigAlarm);
        gSystem->ResetSignal(kSigUrgent);
        gSystem->ResetSignal(kSigFloatingException);
        gSystem->ResetSignal(kSigWindowChanged);
      } else if(pset.getUntrackedParameter<bool>("AbortOnSignal")){
        cachePidInfo();

        //NOTE: ROOT can also be told to abort on these kinds of problems BUT
        // it requires an TApplication to be instantiated which causes problems
        gSystem->ResetSignal(kSigBus);
        gSystem->ResetSignal(kSigSegmentationViolation);
        gSystem->ResetSignal(kSigIllegalInstruction);
        installCustomHandler(SIGBUS,sig_dostack_then_abort);
        sigBusHandler_ = std::shared_ptr<const void>(nullptr,[](void*) {
          installCustomHandler(SIGBUS,sig_abort);
        });
        installCustomHandler(SIGSEGV,sig_dostack_then_abort);
        sigSegvHandler_ = std::shared_ptr<const void>(nullptr,[](void*) {
          installCustomHandler(SIGSEGV,sig_abort);
        });
        installCustomHandler(SIGILL,sig_dostack_then_abort);
        sigIllHandler_ = std::shared_ptr<const void>(nullptr,[](void*) {
          installCustomHandler(SIGILL,sig_abort);
        });
        installCustomHandler(SIGTERM,sig_dostack_then_abort);
        sigTermHandler_ = std::shared_ptr<const void>(nullptr,[](void*) {
          installCustomHandler(SIGTERM,sig_abort);
        });
        installCustomHandler(SIGABRT,sig_dostack_then_abort);
        sigAbrtHandler_ = std::shared_ptr<const void>(nullptr,[](void*) {
          signal(SIGABRT,SIG_DFL); // release SIGABRT to default
        });
      }

      iReg.watchPreallocate([](edm::service::SystemBounds const& iBounds){
        if (iBounds.maxNumberOfThreads() > moduleListBuffers_.size()) {
          moduleListBuffers_.resize(iBounds.maxNumberOfThreads());
        }
      });

      if(resetErrHandler_) {

      // Replace the Root error handler with one that uses the MessageLogger
        SetErrorHandler(RootErrorHandler);
      }

      // Enable automatic Root library loading.
      if(autoLibraryLoader_) {
        gInterpreter->SetClassAutoloading(1);
      }

      // Set ROOT parameters.
      TTree::SetMaxTreeSize(kMaxLong64);
      TH1::AddDirectory(kFALSE);
      //G__SetCatchException(0);

      // Set custom streamers
      setRefCoreStreamerInTClass();

      // Load the library containing dictionaries for std:: classes, if not already loaded.
      if (!hasDictionary(typeid(std::vector<std::vector<unsigned int> >))) {
         TypeWithDict::byName("std::vector<std::vector<unsigned int> >");
      }

      int debugLevel = pset.getUntrackedParameter<int>("DebugLevel");
      if(debugLevel >0) {
    gDebug = debugLevel;
      }

      // Enable Root implicit multi-threading
      bool imt = pset.getUntrackedParameter<bool>("EnableIMT");
      if (imt && not ROOT::IsImplicitMTEnabled()) {
        ROOT::EnableImplicitMT();
      }
    }

    InitRootHandlers::~InitRootHandlers () {
      // close all open ROOT files
      TIter iter(gROOT->GetListOfFiles());
      TObject *obj = nullptr;
      while(nullptr != (obj = iter.Next())) {
        TFile* f = dynamic_cast<TFile*>(obj);
        if(f) {
          // We get a new iterator each time,
          // because closing a file can invalidate the iterator
          f->Close();
          iter = TIter(gROOT->GetListOfFiles());
        }
      }
    }
    
    void InitRootHandlers::willBeUsingThreads() {
      //Tell Root we want to be multi-threaded
      ROOT::EnableThreadSafety();

      //When threading, also have to keep ROOT from logging all TObjects into a list
      TObject::SetObjectStat(false);
      
      //Have to avoid having Streamers modify themselves after they have been used
      TVirtualStreamerInfo::Optimize(false);
    }
    
    void InitRootHandlers::fillDescriptions(ConfigurationDescriptions& descriptions) {
      ParameterSetDescription desc;
      desc.setComment("Centralized interface to ROOT.");
      desc.addUntracked<bool>("UnloadRootSigHandler", false)
          ->setComment("If True, signals are handled by this service, rather than by ROOT.");
      desc.addUntracked<bool>("ResetRootErrHandler", true)
          ->setComment("If True, ROOT messages (e.g. errors, warnings) are handled by this service, rather than by ROOT.");
      desc.addUntracked<bool>("AutoLibraryLoader", true)
          ->setComment("If True, enables automatic loading of data dictionaries.");
      desc.addUntracked<bool>("LoadAllDictionaries",false)
          ->setComment("If True, loads all ROOT dictionaries.");
      desc.addUntracked<bool>("EnableIMT",true)
          ->setComment("If True, calls ROOT::EnableImplicitMT().");
      desc.addUntracked<bool>("AbortOnSignal",true)
          ->setComment("If True, do an abort when a signal occurs that causes a crash. If False, ROOT will do an exit which attempts to do a clean shutdown.");
      desc.addUntracked<int>("DebugLevel",0)
          ->setComment("Sets ROOT's gDebug value.");
      desc.addUntracked<int>("StackTracePauseTime", 300)
          ->setComment("Seconds to pause other threads during stack trace.");
      descriptions.add("InitRootHandlers", desc);
    }

    char *const *
    InitRootHandlers::getPstackArgv() {
      return pstackArgv_;
    }

    void
    InitRootHandlers::enableWarnings_() {
      s_ignoreWarnings = edm::RootHandlers::SeverityLevel::kInfo;
    }

    void
    InitRootHandlers::ignoreWarnings_(edm::RootHandlers::SeverityLevel level) {
      s_ignoreWarnings = level;
    }

    void
    InitRootHandlers::cachePidInfo()
    {
      if(helperThread_) {
        //Another InitRootHandlers was initialized in this job, possibly
        // because multiple EventProcessors are being used.
        //In that case, we are already all setup
        return;
      }
      if (snprintf(pidString_, pidStringLength_-1, "gdb -quiet -p %d 2>&1 <<EOF |\n"
        "set width 0\n"
        "set height 0\n"
        "set pagination no\n"
        "thread apply all bt\n"
        "EOF\n"
        "/bin/sed -n -e 's/^\\((gdb) \\)*//' -e '/^#/p' -e '/^Thread/p'", getpid()) >= pidStringLength_)
      {
        std::ostringstream sstr;
        sstr << "Unable to pre-allocate stacktrace handler information";
        edm::Exception except(edm::errors::OtherCMS, sstr.str());
        throw except;
      }

      // These are initialized to -1; harmless to close an invalid FD.
      // If this is called post-fork, we don't want to be communicating on
      // these FDs as they are used internally by the parent.
      close(childToParent_[0]);
      close(childToParent_[1]);
      childToParent_[0] = -1; childToParent_[1] = -1;
      close(parentToChild_[0]);
      close(parentToChild_[1]);
      parentToChild_[0] = -1; parentToChild_[1] = -1;

      if (-1 == pipe2(childToParent_, O_CLOEXEC))
      {
        std::ostringstream sstr;
        sstr << "Failed to create child-to-parent pipes (errno=" << errno << "): " << strerror(errno);
        edm::Exception except(edm::errors::OtherCMS, sstr.str());
        throw except;
      }

      if (-1 == pipe2(parentToChild_, O_CLOEXEC))
      {
        close(childToParent_[0]); close(childToParent_[1]);
        childToParent_[0] = -1; childToParent_[1] = -1;
        std::ostringstream sstr;
        sstr << "Failed to create child-to-parent pipes (errno=" << errno << "): " << strerror(errno);
        edm::Exception except(edm::errors::OtherCMS, sstr.str());
        throw except;
      }

      helperThread_.reset(new std::thread(stacktraceHelperThread));
      helperThread_->detach();
    }

  }  // end of namespace service
}  // end of namespace edm

using edm::service::InitRootHandlers;
typedef edm::serviceregistry::AllArgsMaker<edm::RootHandlers,InitRootHandlers> RootHandlersMaker;
DEFINE_FWK_SERVICE_MAKER(InitRootHandlers, RootHandlersMaker);