impl/internal/coroutine.hpp

0001 //
0002 // Copyright (c) 2019-2024 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
0003 //
0004 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0005 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 //
0007
0008 #ifndef BOOST_MYSQL_IMPL_INTERNAL_COROUTINE_HPP
0009 #define BOOST_MYSQL_IMPL_INTERNAL_COROUTINE_HPP
0010
0011 // asio::coroutine uses __COUNTER__ internally, which can trigger
0012 // ODR violations if we use them in header-only code. These manifest as
0013 // extremely hard-to-debug bugs only present in release builds
0014
0015 // Coroutine state is represented as an integer (resume_point_var).
0016 // Every yield gets assigned a unique value (resume_point_id).
0017 // Yielding sets the next resume point, returns, and sets a case label for re-entering.
0018 // Coroutines need to switch on resume_point_var to re-enter.
0019
0020 // Enclosing this in a scope allows placing the macro inside a brace-less for/while loop
0021 // The empty scope after the case label is required because labels can't be at the end of a compound statement
0022 #define BOOST_MYSQL_YIELD(resume_point_var, resume_point_id, ...) \
0023     {                                                             \
0024         resume_point_var = resume_point_id;                       \
0025         return __VA_ARGS__;                                       \
0026     case resume_point_id:                                         \
0027     {                                                             \
0028     }                                                             \
0029     }
0030
0031 #define BOOST_MYSQL_YIELD_VOID(resume_point_var, resume_point_id) \
0032     BOOST_MYSQL_YIELD(resume_point_var, resume_point_id, static_cast<void>(0))
0033
0034 #endif