From 0b6810aca783d2fb08e11929672757d73f1b9a7e Mon Sep 17 00:00:00 2001
From: Tristan Brindle <t.c.brindle@gmail.com>
Date: Mon, 9 Sep 2024 19:18:59 +0100
Subject: [PATCH] Add fail_fast runtime error policy

This adds a new fail_fast runtime error policy to go with our existing terminate and unwind policies.

As the name suggests, fail_fast is intended to tear down the process in the fastest way possible should a runtime error occur. It uses `__builtin_trap()` on GCC and Clang, the `__fastfail()` intrinsic on MSVC, and otherwise falls back to `std::abort()`. Unlike the terminate policy, it never attempts to print a message to stderr.
---
 include/flux/core/assert.hpp | 61 +++++++++++++++++++++++++++++-------
 include/flux/core/config.hpp |  8 +++--
 2 files changed, 55 insertions(+), 14 deletions(-)

diff --git a/include/flux/core/assert.hpp b/include/flux/core/assert.hpp
index 5c1416be..76a44982 100644
--- a/include/flux/core/assert.hpp
+++ b/include/flux/core/assert.hpp
@@ -14,6 +14,15 @@
 #include <stdexcept>
 #include <type_traits>
 
+#if defined(__has_builtin)
+#  if __has_builtin(__builtin_trap)
+#    define FLUX_HAS_BUILTIN_TRAP 1
+#  endif
+#elif defined(_MSC_VER)
+#  include <intrin.h>
+#  define FLUX_HAS_FASTFAIL 1
+#endif
+
 namespace flux {
 
 FLUX_EXPORT
@@ -24,21 +33,49 @@ struct unrecoverable_error : std::logic_error {
 namespace detail {
 
 struct runtime_error_fn {
+private:
     [[noreturn]]
-    void operator()(char const* msg,
-                    std::source_location loc = std::source_location::current()) const
+    static inline void fail_fast()
     {
-        if constexpr (config::on_error == error_policy::unwind) {
-            char buf[1024];
-            std::snprintf(buf, 1024, "%s:%u: Fatal error: %s",
-                          loc.file_name(), loc.line(), msg);
-            throw unrecoverable_error(buf);
+#if FLUX_HAS_BUILTIN_TRAP
+        __builtin_trap();
+#elif FLUX_HAS_FASTFAIL
+        __fastfail(7); // FAST_FAIL_FATAL_APP_EXIT
+#else
+        std::abort();
+#endif
+    }
+
+    [[noreturn]]
+    static void unwind(const char* msg, std::source_location loc)
+    {
+        char buf[1024];
+        std::snprintf(buf, 1024, "%s:%u: Fatal error: %s",
+                      loc.file_name(), loc.line(), msg);
+        throw unrecoverable_error(buf);
+    }
+
+    [[noreturn]]
+    static void terminate(const char* msg, std::source_location loc)
+    {
+        if constexpr (config::print_error_on_terminate) {
+            std::fprintf(stderr, "%s:%u: Fatal error: %s\n",
+                         loc.file_name(), loc.line(), msg);
+        }
+        std::terminate();
+    }
+
+public:
+    [[noreturn]]
+    inline void operator()(char const* msg,
+                           std::source_location loc = std::source_location::current()) const
+    {
+        if constexpr (config::on_error == error_policy::fail_fast) {
+            fail_fast();
+        } else if constexpr (config::on_error == error_policy::unwind) {
+            unwind(msg, loc);
         } else {
-            if constexpr (config::print_error_on_terminate) {
-                std::fprintf(stderr, "%s:%u: Fatal error: %s\n",
-                             loc.file_name(), loc.line(), msg);
-            }
-            std::terminate();
+            terminate(msg, loc);
         }
     }
 };
diff --git a/include/flux/core/config.hpp b/include/flux/core/config.hpp
index 322b663e..92d7af72 100644
--- a/include/flux/core/config.hpp
+++ b/include/flux/core/config.hpp
@@ -13,7 +13,8 @@
 #include <type_traits>
 
 #define FLUX_ERROR_POLICY_TERMINATE 1
-#define FLUX_ERROR_POLICY_UNWIND     2
+#define FLUX_ERROR_POLICY_UNWIND    2
+#define FLUX_ERROR_POLICY_FAIL_FAST 3
 
 #define FLUX_OVERFLOW_POLICY_ERROR   10
 #define FLUX_OVERFLOW_POLICY_WRAP    11
@@ -47,6 +48,8 @@
 #  define FLUX_ERROR_POLICY FLUX_ERROR_POLICY_TERMINATE
 #elif defined(FLUX_UNWIND_ON_ERROR)
 #  define FLUX_ERROR_POLICY FLUX_ERROR_POLICY_UNWIND
+#elif defined(FLUX_FAIL_FAST_ON_ERROR)
+#  define FLUX_ERROR_POLICY FLUX_ERROR_POLICY_FAIL_FAST
 #else
 #  define FLUX_ERROR_POLICY FLUX_DEFAULT_ERROR_POLICY
 #endif // FLUX_TERMINATE_ON_ERROR
@@ -123,7 +126,8 @@ namespace flux {
 FLUX_EXPORT
 enum class error_policy {
     terminate = FLUX_ERROR_POLICY_TERMINATE,
-    unwind = FLUX_ERROR_POLICY_UNWIND
+    unwind = FLUX_ERROR_POLICY_UNWIND,
+    fail_fast = FLUX_ERROR_POLICY_FAIL_FAST
 };
 
 FLUX_EXPORT