asio/detail/executor_function.hpp

0001 //
0002 // detail/executor_function.hpp
0003 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0004 //
0005 // Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
0006 //
0007 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0008 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0009 //
0010
0011 #ifndef BOOST_ASIO_DETAIL_EXECUTOR_FUNCTION_HPP
0012 #define BOOST_ASIO_DETAIL_EXECUTOR_FUNCTION_HPP
0013
0014 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
0015 # pragma once
0016 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
0017
0018 #include <boost/asio/detail/config.hpp>
0019 #include <boost/asio/detail/handler_alloc_helpers.hpp>
0020 #include <boost/asio/detail/memory.hpp>
0021
0022 #include <boost/asio/detail/push_options.hpp>
0023
0024 namespace boost {
0025 namespace asio {
0026 namespace detail {
0027
0028 // Lightweight, move-only function object wrapper.
0029 class executor_function
0030 {
0031 public:
0032   template <typename F, typename Alloc>
0033   explicit executor_function(F f, const Alloc& a)
0034   {
0035     // Allocate and construct an object to wrap the function.
0036     typedef impl<F, Alloc> impl_type;
0037     typename impl_type::ptr p = {
0038       detail::addressof(a), impl_type::ptr::allocate(a), 0 };
0039     impl_ = new (p.v) impl_type(static_cast<F&&>(f), a);
0040     p.v = 0;
0041   }
0042
0043   executor_function(executor_function&& other) noexcept
0044     : impl_(other.impl_)
0045   {
0046     other.impl_ = 0;
0047   }
0048
0049   ~executor_function()
0050   {
0051     if (impl_)
0052       impl_->complete_(impl_, false);
0053   }
0054
0055   void operator()()
0056   {
0057     if (impl_)
0058     {
0059       impl_base* i = impl_;
0060       impl_ = 0;
0061       i->complete_(i, true);
0062     }
0063   }
0064
0065 private:
0066   // Base class for polymorphic function implementations.
0067   struct impl_base
0068   {
0069     void (*complete_)(impl_base*, bool);
0070   };
0071
0072   // Polymorphic function implementation.
0073   template <typename Function, typename Alloc>
0074   struct impl : impl_base
0075   {
0076     BOOST_ASIO_DEFINE_TAGGED_HANDLER_ALLOCATOR_PTR(
0077         thread_info_base::executor_function_tag, impl);
0078
0079     template <typename F>
0080     impl(F&& f, const Alloc& a)
0081       : function_(static_cast<F&&>(f)),
0082         allocator_(a)
0083     {
0084       complete_ = &executor_function::complete<Function, Alloc>;
0085     }
0086
0087     Function function_;
0088     Alloc allocator_;
0089   };
0090
0091   // Helper to complete function invocation.
0092   template <typename Function, typename Alloc>
0093   static void complete(impl_base* base, bool call)
0094   {
0095     // Take ownership of the function object.
0096     impl<Function, Alloc>* i(static_cast<impl<Function, Alloc>*>(base));
0097     Alloc allocator(i->allocator_);
0098     typename impl<Function, Alloc>::ptr p = {
0099       detail::addressof(allocator), i, i };
0100
0101     // Make a copy of the function so that the memory can be deallocated before
0102     // the upcall is made. Even if we're not about to make an upcall, a
0103     // sub-object of the function may be the true owner of the memory
0104     // associated with the function. Consequently, a local copy of the function
0105     // is required to ensure that any owning sub-object remains valid until
0106     // after we have deallocated the memory here.
0107     Function function(static_cast<Function&&>(i->function_));
0108     p.reset();
0109
0110     // Make the upcall if required.
0111     if (call)
0112     {
0113       static_cast<Function&&>(function)();
0114     }
0115   }
0116
0117   impl_base* impl_;
0118 };
0119
0120 // Lightweight, non-owning, copyable function object wrapper.
0121 class executor_function_view
0122 {
0123 public:
0124   template <typename F>
0125   explicit executor_function_view(F& f) noexcept
0126     : complete_(&executor_function_view::complete<F>),
0127       function_(&f)
0128   {
0129   }
0130
0131   void operator()()
0132   {
0133     complete_(function_);
0134   }
0135
0136 private:
0137   // Helper to complete function invocation.
0138   template <typename F>
0139   static void complete(void* f)
0140   {
0141     (*static_cast<F*>(f))();
0142   }
0143
0144   void (*complete_)(void*);
0145   void* function_;
0146 };
0147
0148 } // namespace detail
0149 } // namespace asio
0150 } // namespace boost
0151
0152 #include <boost/asio/detail/pop_options.hpp>
0153
0154 #endif // BOOST_ASIO_DETAIL_EXECUTOR_FUNCTION_HPP