The Absurdity of Error Handling: Finding a Purpose for Errors in Safety-Critical SYCL Erik Tomusk CppCon 2023 October 5, 2023© 2023 Codeplay Software Ltd. Codeplay Corporate Slide 2© 2023 Codeplay explicitly stated© 2023 Codeplay Software Ltd. Outline • Definition of Safety • Definition of Error Handling • Case Study • Why is this Important? • Is it Really so bad? • What does this mean for SYCL execution time (in mainstream compilers) 17Definition of Error Handling 18© 2023 Codeplay Software Ltd. Definition of Error Handling • Exceptions and error codes are sometimes used for reporting or information

Modern C++ Handling Phil Nash Error2018 2019series disappointments of a (total) Part 1int parse_int(std::string_view number)// TODO: +, -, digit separators? int acc = 0; for(char c first_digit = false; } return ParseStatus::Numeric; } 42 42 (starts with an int) Error: x42 is not an int test("42"); test("42x"); test("x42"); [[nodiscard]] void test(std::string_view int)”, i); break; case ParseStatus::NonNumeric: std::println(“Error: {} is not an int", str); break; } }int parse_int(std::string_view number) {

Design patterns for error handling in C++ programs using parallel algorithms and executors Mark Hoemmen* mhoemmen@stellarscience.com CppCon 2020 * hoʊ’mən, or hœm’mən; he/himWho am I? • > 10 years Started new job at Stellar Science in March Eschew raw pointersOutline • Parallelism makes error handling harder… • …C++ parallel algorithms and tasks specifically • Message Passing Interface (MPI): Steve Jurvetson)Parallel hinders error handling • … because parallelism relaxes execution order – Deliberately, to improve performance • Errors interrupt execution; handling constrains order • Errors could

CppCon 2024 Customizing Compilation Error Messages Formatting a Compile-Time String During Substitution Failure Patrick Roberts, P.E. Principal Software Engineer 1CppCon 2024 What problem does solve? 2CppCon 2024 3CppCon 2024 4CppCon 2024 5CppCon 2024 6 Guidelines for a helpful error message Where is the error? ✅ What is wrong? ✅ How can it be fixed? ❌CppCon 2024 7CppCon 2024 8CppCon 2024 9

Message Handling with Boolean Algebra Ben Deane / CppCon / 2024-09-16 1Alternative Title "The Unreasonable Effectiveness of Boolean Algebra in Software Design, Showing the Particular Application of of a Message Handling Library, with an Excursion into the Roots of Programming" 2Frontmatter No AI/LLM was used in the creation of this talk. Code is simplified for slides; may have some errors in ] SVG diagrams for resolution-independence 4What this talk is about The workings of a message-handling library. How messages and the fields in them are specified. Efficiently identifying (with matchers)

std::shared_ptr response) { if (map_.get_data().size() == 0) { RCLCPP_ERROR_STREAM(this->get_logger(), "MAP IS EMPTY!!"); response->code.code = example_srvs::msg::GetPat _OCCUPANCY_MAP; response->path = std_msgs::msg::UInt8MultiArray(); return; } /* More error pre-checks */ auto const start = Position{request->start.data[0], request->start.data[1]}; auto std::shared_ptr response) { if (map_.get_data().size() == 0) { RCLCPP_ERROR_STREAM(this->get_logger(), "MAP IS EMPTY!!"); response->code.code = example_srvs::msg::GetPat

(Such as Embedded, GPUs and Gaming) avoid using exceptions for performance reasons. • The error handling mechanism was addressed by C++’s Direction group around 2016 (contracts) and again in 2018 decision making described is alleged, I wasn’t there.  6PART 0: WHAT ARE EXCEPTIONS 7• A fail-handling mechanism void foo() { // do stuff that can fail if (fail) { // throw } } PART 0: WHAT ARE throw by value, catch by const ref, and re-throw using throw.• A fail-handling mechanism void bar() { try { foo(); } catch (error_type) { // do stuff, or re-throw; } catch (…) { // do stuff, or re-throw;

goals/ideals of exception handling • Look at the mechanics of throw/catch • Look at Exceptions in both their use and design as seen in real code • Better thinking on the handling of error use cases • Better Decouples error reporting from error handling • Exceptions can’t be passively ignored * • Simpler way for handling constructor and operator errors • Modern and “recommended” way of error handling in the language = 21}; if(me.notValid()) { std::cout << "error : Object invalid" << me << std::endl; exit(-1); } MyStatus rc = applyX(me); if(rc != good) std::cout << "error : " << rc << std::endl; … } } Clutter

System structure • Parts of an implementation • Interfaces • Messages • Vectors and strings • Error handling • Observations • C++ is quite good at this • But not perfect, we’ll continue to improve it mapping • Keeping track of type mappings is not fit for humans • High -> low -> high • Fiddly, error-prone • So we generate such interface code // initializer for an Vector called vs: void Run-time support library • Flat types: Vector, String, Array, Variant, Optional, Span, Span_ref • Error handling Stroustrup - "Primitive" - CppCon 2020 23 Red: mentioned hereInterfaces • Good interfaces

Learn More? i2c-bus.org 23 STOPPossible I2C Errors 24 ⚠ 󰢃 ADDR NACK Device Not Present IO ERROR Unexpected Bus State ADDRESS (7-bit) Byte 0 STA NACK/ ACK W/R ACK Byte 1 ACK NACK STOPLet's consider std::expectederror_t>30 std::expected #include enum class my_error { precondition_violated, invalid_arguments, // etc ... }; std::expectederror> get_version() { if (device_disconnected) { return std::unexpected(my_error::precondition_violated); } return 15; }void toggle_led(output_pin& p_pin, milliseconds p_transition_time) { p_pin.level(true);