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Diffstat (limited to '3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp')
-rw-r--r-- | 3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp b/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp new file mode 100644 index 00000000000..15422454c40 --- /dev/null +++ b/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp @@ -0,0 +1,131 @@ +// +// composed_2.cpp +// ~~~~~~~~~~~~~~ +// +// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com) +// +// Distributed under the Boost Software License, Version 1.0. (See accompanying +// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) +// + +#include <asio/io_context.hpp> +#include <asio/ip/tcp.hpp> +#include <asio/use_future.hpp> +#include <asio/write.hpp> +#include <cstring> +#include <iostream> +#include <string> +#include <type_traits> +#include <utility> + +using asio::ip::tcp; + +//------------------------------------------------------------------------------ + +// This next simplest example of a composed asynchronous operation involves +// repackaging multiple operations but choosing to invoke just one of them. All +// of these underlying operations have the same completion signature. The +// asynchronous operation requirements are met by delegating responsibility to +// the underlying operations. + +template <typename CompletionToken> +auto async_write_message(tcp::socket& socket, + const char* message, bool allow_partial_write, + CompletionToken&& token) + // The return type of the initiating function is deduced from the combination + // of CompletionToken type and the completion handler's signature. When the + // completion token is a simple callback, the return type is void. However, + // when the completion token is asio::yield_context (used for stackful + // coroutines) the return type would be std::size_t, and when the completion + // token is asio::use_future it would be std::future<std::size_t>. + // + // In C++14 we can omit the return type as it is automatically deduced from + // the return type of our underlying asynchronous operation +{ + // As the return type of the initiating function is deduced solely from the + // CompletionToken and completion signature, we know that two different + // asynchronous operations having the same completion signature will produce + // the same return type, when passed the same CompletionToken. This allows us + // to trivially delegate to alternate implementations. + if (allow_partial_write) + { + // When delegating to an underlying operation we must take care to + // perfectly forward the completion token. This ensures that our operation + // works correctly with move-only function objects as callbacks, as well as + // other completion token types. + return socket.async_write_some( + asio::buffer(message, std::strlen(message)), + std::forward<CompletionToken>(token)); + } + else + { + // As above, we must perfectly forward the completion token when calling + // the alternate underlying operation. + return asio::async_write(socket, + asio::buffer(message, std::strlen(message)), + std::forward<CompletionToken>(token)); + } +} + +//------------------------------------------------------------------------------ + +void test_callback() +{ + asio::io_context io_context; + + tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); + tcp::socket socket = acceptor.accept(); + + // Test our asynchronous operation using a lambda as a callback. + async_write_message(socket, "Testing callback\r\n", false, + [](const std::error_code& error, std::size_t n) + { + if (!error) + { + std::cout << n << " bytes transferred\n"; + } + else + { + std::cout << "Error: " << error.message() << "\n"; + } + }); + + io_context.run(); +} + +//------------------------------------------------------------------------------ + +void test_future() +{ + asio::io_context io_context; + + tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); + tcp::socket socket = acceptor.accept(); + + // Test our asynchronous operation using the use_future completion token. + // This token causes the operation's initiating function to return a future, + // which may be used to synchronously wait for the result of the operation. + std::future<std::size_t> f = async_write_message( + socket, "Testing future\r\n", false, asio::use_future); + + io_context.run(); + + try + { + // Get the result of the operation. + std::size_t n = f.get(); + std::cout << n << " bytes transferred\n"; + } + catch (const std::exception& e) + { + std::cout << "Error: " << e.what() << "\n"; + } +} + +//------------------------------------------------------------------------------ + +int main() +{ + test_callback(); + test_future(); +} |