__debugbreak in windows can easily cause recursive crashes if you are

NOT in debug mode in your visual IDE

example/main_fatal_choice.cpp

@@ -233,10 +233,18 @@ void ChooseFatalExit() {
 }
 } // namespace
 
+void breakHere() {
+ #if (defined(WIN32) || defined(_WIN32) || defined(__WIN32__))
+   __debugbreak(); 
+ #endif
+}
+
 int main(int argc, char** argv)
 {
    auto logger_n_handle = g2::LogWorker::createWithDefaultLogger(argv[0], path_to_log_file);
    g2::initializeLogging(logger_n_handle.worker.get());
+   g2::setFatalPreLoggingHook(&breakHere);
+
    std::future<std::string> log_file_name = logger_n_handle.sink->call(&g2::FileSink::fileName);
    std::cout << "**** G3LOG FATAL EXAMPLE ***\n\n"
              << "Choose your type of fatal exit, then "

src/g2log.cpp

@@ -41,6 +41,8 @@ std::once_flag g_save_first_unintialized_flag;
 const std::function<void(void)> g_pre_fatal_hook_that_does_nothing = []{ /*does nothing */};
 std::function<void(void)> g_fatal_pre_logging_hook;
 
+
+g2_thread_local size_t g_fatal_hook_recursive_counter = {0};
 }
 
 
@@ -82,6 +84,8 @@ void initializeLogging(LogWorker* bgworker) {
 *     so please call this function, if you ever need to, after initializeLogging(...)
 */
 void setFatalPreLoggingHook(std::function<void(void)>  pre_fatal_hook) {
+   static std::mutex m;
+   std::lock_guard<std::mutex> lock(m);
    g_fatal_pre_logging_hook = pre_fatal_hook;
 }
 
@@ -138,6 +142,7 @@ bool shutDownLoggingForActiveOnly(LogWorker* active) {
 
 
 
+
 /** explicits copy of all input. This is makes it possibly to use g3log across dynamically loaded libraries
 * i.e. (dlopen + dlsym)  */
 void saveMessage(const char* entry, const char* file, int line, const char* function, const LEVELS& level,
@@ -147,11 +152,28 @@ void saveMessage(const char* entry, const char* file, int line, const char* func
    message.get()->write().append(entry);
    message.get()->setExpression(boolean_expression);
 
-   if (internal::wasFatal(level)) {
-      message.get()->write().append(stack_trace);
-      FatalMessagePtr fatal_message {std2::make_unique<FatalMessage>(*(message._move_only.get()), fatal_signal)};
-      g_fatal_pre_logging_hook(); // pre-fatal hook
 
+   if (internal::wasFatal(level)) {
+      auto fatalhook = g_fatal_pre_logging_hook;
+      // In case the fatal_pre logging actually will cause a crash in its turn
+      // let's not do recursive crashing!
+      setFatalPreLoggingHook(g_pre_fatal_hook_that_does_nothing);
+      ++g_fatal_hook_recursive_counter; // thread_local counter
+      // "benign" race here. If two threads crashes, with recursive crashes
+      // then it's possible that the "other" fatal stack trace will be shown
+      // that's OK since it was anyhow the first crash detected
+      static const std::string first_stack_trace = stack_trace;
+      fatalhook();
+      message.get()->write().append(stack_trace);
+
+      if (g_fatal_hook_recursive_counter > 1) {
+         message.get()->write()
+            .append("\n\n\nWARNING\n"
+            "A recursive crash detected. It is likely the hook set with 'setFatalPreLoggingHook(...)' is responsible\n\n")
+            .append("---First crash stacktrace: ").append(first_stack_trace).append("\n---End of first stacktrace\n");
+
+      }
+      FatalMessagePtr fatal_message{ std2::make_unique<FatalMessage>(*(message._move_only.get()), fatal_signal) };
       // At destruction, flushes fatal message to g2LogWorker
       // either we will stay here until the background worker has received the fatal
       // message, flushed the crash message to the sinks and exits with the same fatal signal

src/g2log.hpp

@@ -33,6 +33,16 @@
 #define __PRETTY_FUNCTION__   __FUNCTION__
 #endif
 
+
+// thread_local doesn't exist on VS2013 but it might soon? (who knows)
+// to avoid future issues, let's define g2_thread_local that should continue
+// to work after Microsoft has updated to be C++11 compliant
+#if (defined(WIN32) || defined(_WIN32) || defined(__WIN32__))
+#define g2_thread_local __declspec(thread) 
+#else 
+#define g2_thread_local thread_local
+#endif
+
 /** namespace for LOG() and CHECK() frameworks
  * History lesson:   Why the names 'g2' and 'g2log'?:
  * The framework was made in my own free time as PUBLIC DOMAIN but the 
@@ -62,8 +72,8 @@ namespace g2 {
    * This will be reset to default (does nothing) at initializeLogging(...);
    *
    * Example usage:
-   * Windows: g2::SetPreFatalHook([]{__debugbreak();}); // remember #include <intrin.h>
+   * Windows: g2::setFatalPreLoggingHook([]{__debugbreak();}); // remember #include <intrin.h>
-   * Linux:   g2::SetPreFatalHook([]{ raise(SIGTRAP); }); 
+   * Linux:   g2::setFatalPreLoggingHook([]{ raise(SIGTRAP); }); 
    */
    void setFatalPreLoggingHook(std::function<void(void)>  pre_fatal_hook);
 

src/stacktrace_windows.cpp

@@ -13,6 +13,7 @@
  * ============================================================================*/
 
 #include "stacktrace_windows.hpp"
+#include "g2log.hpp"
 #include <windows.h>
 #include <DbgHelp.h>
 #include <map>
@@ -39,7 +40,6 @@ g2_thread_local size_t g_thread_local_recursive_crash_check = 0;
 const std::map<g2::SignalType, std::string> kExceptionsAsText = {
    g2_MAP_PAIR_STRINGIFY(EXCEPTION_ACCESS_VIOLATION)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_ARRAY_BOUNDS_EXCEEDED)
-   , g2_MAP_PAIR_STRINGIFY(EXCEPTION_BREAKPOINT)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_DATATYPE_MISALIGNMENT)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_FLT_DENORMAL_OPERAND)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_FLT_DIVIDE_BY_ZERO)
@@ -56,8 +56,10 @@ const std::map<g2::SignalType, std::string> kExceptionsAsText = {
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_INVALID_DISPOSITION)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_NONCONTINUABLE_EXCEPTION)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_PRIV_INSTRUCTION)
-   , g2_MAP_PAIR_STRINGIFY(EXCEPTION_SINGLE_STEP)
    , g2_MAP_PAIR_STRINGIFY(EXCEPTION_STACK_OVERFLOW)
+   , g2_MAP_PAIR_STRINGIFY(EXCEPTION_BREAKPOINT)
+   , g2_MAP_PAIR_STRINGIFY(EXCEPTION_SINGLE_STEP)
+
 };
 
 

src/stacktrace_windows.hpp

@@ -17,8 +17,6 @@
 #error "stacktrace_win.cpp used but not on a windows system"
 #endif
 
-#define g2_thread_local __declspec(thread) 
-
 #include <string>
 #include <windows.h>
 #include "crashhandler.hpp"