7142b1a08d
Generalize error handling by creating exception dispatcher which allows to write error handlers by sequentially applying handlers the same way one would write `catch ()` blocks
287 lines
9.2 KiB
C++
287 lines
9.2 KiB
C++
/*
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* Copyright 2016-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*/
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#pragma once
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// for checking __GLIBCXX__
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#include <version>
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#if defined(__GLIBCXX__) && (defined(__x86_64__) || defined(__aarch64__))
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#define OPTIMIZED_EXCEPTION_HANDLING_AVAILABLE
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#endif
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#if !defined(NO_OPTIMIZED_EXCEPTION_HANDLING)
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#if defined(OPTIMIZED_EXCEPTION_HANDLING_AVAILABLE)
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#define USE_OPTIMIZED_EXCEPTION_HANDLING
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#else
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#warning "Fast implementation of some of the exception handling routines is not available for this platform. Expect poor exception handling performance."
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#endif
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#endif
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#include <seastar/core/align.hh>
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#include <functional>
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#include <optional>
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#include <system_error>
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#include <type_traits>
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namespace seastar { class logger; }
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typedef std::function<bool (const std::system_error &)> system_error_lambda_t;
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bool check_exception(system_error_lambda_t f);
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bool is_system_error_errno(int err_no);
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bool is_timeout_exception(std::exception_ptr e);
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class storage_io_error : public std::exception {
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private:
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std::error_code _code;
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std::string _what;
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public:
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storage_io_error(std::error_code c, std::string s) noexcept
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: _code(std::move(c))
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, _what(std::move(s))
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{ }
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storage_io_error(int err, std::string s) noexcept
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: storage_io_error(std::error_code(err, std::system_category()), std::move(s))
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{ }
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storage_io_error(std::system_error& e) noexcept
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: storage_io_error(e.code(), std::string("Storage I/O error: ") + std::to_string(e.code().value()) + ": " + e.what())
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{ }
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virtual const char* what() const noexcept override {
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return _what.c_str();
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}
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const std::error_code& code() const noexcept { return _code; }
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};
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// Rethrow exception if not null
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//
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// Helps with the common coroutine exception-handling idiom:
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//
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// std::exception_ptr ex;
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// try {
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// ...
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// } catch (...) {
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// ex = std::current_exception();
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// }
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//
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// // release resource(s)
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// maybe_rethrow_exception(std::move(ex));
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//
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// return result;
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//
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inline void maybe_rethrow_exception(std::exception_ptr ex) {
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if (ex) {
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std::rethrow_exception(std::move(ex));
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}
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}
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namespace utils::internal {
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#if defined(OPTIMIZED_EXCEPTION_HANDLING_AVAILABLE)
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void* try_catch_dynamic(std::exception_ptr& eptr, const std::type_info* catch_type) noexcept;
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using default_nested_exception_type = std::runtime_error;
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template<typename Ex>
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class nested_exception : public Ex, public std::nested_exception {
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private:
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void set_nested_exception(std::exception_ptr nested_eptr) {
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// Hack: libstdc++'s std::nested_exception has just one field
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// which is a std::exception_ptr. It is initialized
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// to std::current_exception on its construction, but we override
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// it here.
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auto* nex = dynamic_cast<std::nested_exception*>(this);
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// std::nested_exception is virtual without any base classes,
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// so according to the ABI we just need to skip the vtable pointer
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// and align
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auto* nptr = reinterpret_cast<std::exception_ptr*>(
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seastar::align_up(
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reinterpret_cast<char*>(nex) + sizeof(void*),
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alignof(std::nested_exception)));
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*nptr = std::move(nested_eptr);
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}
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public:
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explicit nested_exception(const Ex& ex, std::exception_ptr&& nested_eptr)
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: Ex(ex) {
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set_nested_exception(std::move(nested_eptr));
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}
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explicit nested_exception(Ex&& ex, std::exception&& nested_eptr)
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: Ex(std::move(ex)) {
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set_nested_exception(std::move(nested_eptr));
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}
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};
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#endif
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} // utils::internal
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/// If the exception_ptr holds an exception which would match on a `catch (T&)`
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/// clause, returns a pointer to it. Otherwise, returns `nullptr`.
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///
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/// The exception behind the pointer is valid as long as the exception
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/// behind the exception_ptr is valid.
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template<typename T>
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inline T* try_catch(std::exception_ptr& eptr) noexcept {
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static_assert(!std::is_pointer_v<T>, "catching pointers is not supported");
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static_assert(!std::is_lvalue_reference_v<T> && !std::is_rvalue_reference_v<T>,
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"T must not be a reference");
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#if defined(USE_OPTIMIZED_EXCEPTION_HANDLING)
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void* opt_ptr = utils::internal::try_catch_dynamic(eptr, &typeid(std::remove_const_t<T>));
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return reinterpret_cast<T*>(opt_ptr);
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#else
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try {
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std::rethrow_exception(eptr);
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} catch (T& t) {
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return &t;
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} catch (...) {
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}
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return nullptr;
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#endif
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}
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/// The same as try_catch, but also unwraps if the exception was nested.
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template <typename TException>
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inline TException* try_catch_nested(std::exception_ptr& eptr) noexcept {
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// Check if we got the exception we were looking for in the upper level.
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auto* non_nested = try_catch<TException>(eptr);
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if (non_nested) {
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return non_nested;
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}
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// Go through all the wrapped levels until we find the requested exception.
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std::exception_ptr parent_eptr = eptr;
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std::exception_ptr nested_eptr;
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std::nested_exception* nested{nullptr};
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while (parent_eptr && (nested = try_catch<std::nested_exception>(parent_eptr)) && (nested_eptr = nested->nested_ptr())) {
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auto* res = try_catch<TException>(nested_eptr);
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if (res) {
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return res;
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}
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parent_eptr = nested_eptr;
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}
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return nullptr;
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}
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/// Analogous to std::throw_with_nested, but instead of capturing the currently
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/// thrown exception, takes the exception to be nested inside as an argument,
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/// and does not throw the new exception but rather returns it.
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template<typename Ex>
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inline std::exception_ptr make_nested_exception_ptr(Ex&& ex, std::exception_ptr nested) {
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using ExDecayed = std::decay_t<Ex>;
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static_assert(std::is_copy_constructible_v<ExDecayed> && std::is_move_constructible_v<ExDecayed>,
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"make_nested_exception_ptr argument must be CopyConstructible");
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#if defined(USE_OPTIMIZED_EXCEPTION_HANDLING)
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// std::rethrow_with_nested wraps the exception type if and only if
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// it is a non-final non-union class type
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// and is neither std::nested_exception nor derived from it.
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// Ref: https://en.cppreference.com/w/cpp/error/throw_with_nested
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constexpr bool wrap = std::is_class_v<ExDecayed>
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&& !std::is_final_v<ExDecayed>
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&& !std::is_base_of_v<std::nested_exception, ExDecayed>;
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if constexpr (wrap) {
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return std::make_exception_ptr(utils::internal::nested_exception<ExDecayed>(
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std::forward<Ex>(ex), std::move(nested)));
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} else {
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return std::make_exception_ptr<Ex>(std::forward<Ex>(ex));
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}
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#else
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try {
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std::rethrow_exception(std::move(nested));
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} catch (...) {
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try {
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std::throw_with_nested(std::forward<Ex>(ex));
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} catch (...) {
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return std::current_exception();
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}
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}
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#endif
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}
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namespace exception::internal {
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template <typename F>
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struct lambda_arg;
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template <typename R, typename C, typename Arg>
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struct lambda_arg<R (C::*)(Arg) const> {
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using type = Arg;
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};
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template <typename F>
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using lambda_arg_t = std::remove_cvref_t<typename lambda_arg<decltype(&F::operator())>::type>;
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} // namespace exception::internal
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// dispatch_exception: unwraps nested exceptions (if any) and applies handlers
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// The dispatcher gets as input the exception_ptr to process, a default handler
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// to call if no other handler matches, and a variadic list of TypedHandlers.
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// All handlers (including the default one) must return the same type R.
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template <typename R, typename DefaultHandler, typename... Handlers>
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requires std::is_same_v<R, std::invoke_result_t<DefaultHandler, std::exception_ptr, std::string&&>> &&
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(std::is_same_v<R, std::invoke_result_t<Handlers, const exception::internal::lambda_arg_t<Handlers>&>> && ...)
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R dispatch_exception(std::exception_ptr eptr, DefaultHandler&& default_handler, Handlers&&... handlers) {
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std::string original_message;
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while (eptr) {
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try {
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std::rethrow_exception(eptr);
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} catch (const std::exception& e) {
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if (original_message.empty()) {
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original_message = e.what();
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}
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std::optional<R> result;
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(
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[&] {
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using F = std::decay_t<Handlers>;
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using Arg = exception::internal::lambda_arg_t<F>;
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if constexpr (std::is_base_of_v<std::exception, Arg>) {
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if (!result) {
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if (auto* casted = dynamic_cast<const Arg*>(&e)) {
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result = handlers(*casted);
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}
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}
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}
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}(),
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...);
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if (result) {
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return *result;
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}
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// Try to unwrap nested exception
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try {
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std::rethrow_if_nested(e);
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} catch (...) {
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eptr = std::current_exception();
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continue;
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}
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return default_handler(eptr, std::move(original_message));
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} catch (...) {
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return default_handler(eptr, std::move(original_message));
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}
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}
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return default_handler(eptr, std::move(original_message));
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}
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