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-rw-r--r--3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp146
1 files changed, 117 insertions, 29 deletions
diff --git a/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp b/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp
index 15422454c40..18086bd0627 100644
--- a/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp
+++ b/3rdparty/asio/src/examples/cpp14/operations/composed_2.cpp
@@ -2,12 +2,13 @@
// composed_2.cpp
// ~~~~~~~~~~~~~~
//
-// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2003-2024 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/deferred.hpp>
#include <asio/io_context.hpp>
#include <asio/ip/tcp.hpp>
#include <asio/use_future.hpp>
@@ -20,6 +21,10 @@
using asio::ip::tcp;
+// NOTE: This example requires the new asio::async_initiate function. For
+// an example that works with the Networking TS style of completion tokens,
+// please see an older version of asio.
+
//------------------------------------------------------------------------------
// This next simplest example of a composed asynchronous operation involves
@@ -33,38 +38,87 @@ 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>.
+ // of:
+ //
+ // - the CompletionToken type,
+ // - the completion handler signature, and
+ // - the asynchronous operation's initiation function object.
+ //
+ // 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>.
+ // When the completion token is asio::deferred, the return type differs for
+ // each asynchronous operation.
//
// In C++14 we can omit the return type as it is automatically deduced from
- // the return type of our underlying asynchronous operation
+ // the return type of asio::async_initiate.
{
- // 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
+ // In addition to determining the mechanism by which an asynchronous
+ // operation delivers its result, a completion token also determines the time
+ // when the operation commences. For example, when the completion token is a
+ // simple callback the operation commences before the initiating function
+ // returns. However, if the completion token's delivery mechanism uses a
+ // future, we might instead want to defer initiation of the operation until
+ // the returned future object is waited upon.
+ //
+ // To enable this, when implementing an asynchronous operation we must
+ // package the initiation step as a function object. The initiation function
+ // object's call operator is passed the concrete completion handler produced
+ // by the completion token. This completion handler matches the asynchronous
+ // operation's completion handler signature, which in this example is:
+ //
+ // void(std::error_code error, std::size_t)
+ //
+ // The initiation function object also receives any additional arguments
+ // required to start the operation. (Note: We could have instead passed these
+ // arguments in the lambda capture set. However, we should prefer to
+ // propagate them as function call arguments as this allows the completion
+ // token to optimise how they are passed. For example, a lazy future which
+ // defers initiation would need to make a decay-copy of the arguments, but
+ // when using a simple callback the arguments can be trivially forwarded
+ // straight through.)
+ auto initiation = [](auto&& completion_handler, tcp::socket& socket,
+ const char* message, bool allow_partial_write)
{
- // 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));
- }
+ if (allow_partial_write)
+ {
+ // When delegating to an underlying operation we must take care to
+ // perfectly forward the completion handler. This ensures that our
+ // operation works correctly with move-only function objects as
+ // callbacks.
+ return socket.async_write_some(
+ asio::buffer(message, std::strlen(message)),
+ std::forward<decltype(completion_handler)>(completion_handler));
+ }
+ else
+ {
+ // As above, we must perfectly forward the completion handler when calling
+ // the alternate underlying operation.
+ return asio::async_write(socket,
+ asio::buffer(message, std::strlen(message)),
+ std::forward<decltype(completion_handler)>(completion_handler));
+ }
+ };
+
+ // The asio::async_initiate function takes:
+ //
+ // - our initiation function object,
+ // - the completion token,
+ // - the completion handler signature, and
+ // - any additional arguments we need to initiate the operation.
+ //
+ // It then asks the completion token to create a completion handler (i.e. a
+ // callback) with the specified signature, and invoke the initiation function
+ // object with this completion handler as well as the additional arguments.
+ // The return value of async_initiate is the result of our operation's
+ // initiating function.
+ //
+ // Note that we wrap non-const reference arguments in std::reference_wrapper
+ // to prevent incorrect decay-copies of these objects.
+ return asio::async_initiate<
+ CompletionToken, void(std::error_code, std::size_t)>(
+ initiation, token, std::ref(socket), message, allow_partial_write);
}
//------------------------------------------------------------------------------
@@ -95,6 +149,39 @@ void test_callback()
//------------------------------------------------------------------------------
+void test_deferred()
+{
+ asio::io_context io_context;
+
+ tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
+ tcp::socket socket = acceptor.accept();
+
+ // Test our asynchronous operation using the deferred completion token. This
+ // token causes the operation's initiating function to package up the
+ // operation with its arguments to return a function object, which may then be
+ // used to launch the asynchronous operation.
+ auto op = async_write_message(socket,
+ "Testing deferred\r\n", false, asio::deferred);
+
+ // Launch the operation using a lambda as a callback.
+ std::move(op)(
+ [](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;
@@ -127,5 +214,6 @@ void test_future()
int main()
{
test_callback();
+ test_deferred();
test_future();
}