asio/src/examples/cpp14/operations/composed_6.cpp - third_party/asio - Git at Google

 //
 // composed_6.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/executor_work_guard.hpp>
 #include <asio/io_context.hpp>
 #include <asio/ip/tcp.hpp>
 #include <asio/steady_timer.hpp>
 #include <asio/use_future.hpp>
 #include <asio/write.hpp>
 #include <functional>
 #include <iostream>
 #include <memory>
 #include <sstream>
 #include <string>
 #include <type_traits>
 #include <utility>

 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 composed operation shows composition of multiple underlying operations.
 // It automatically serialises a message, using its I/O streams insertion
 // operator, before sending it N times on the socket. To do this, it must
 // allocate a buffer for the encoded message and ensure this buffer's validity
 // until all underlying async_write operation complete. A one second delay is
 // inserted prior to each write operation, using a steady_timer.

 template <typename T, typename CompletionToken>
 auto async_write_messages(tcp::socket& socket,
     const T& message, std::size_t repeat_count,
     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 always void.
   // In this example, when the completion token is asio::yield_context
   // (used for stackful coroutines) the return type would be also be void, as
   // there is no non-error argument to the completion handler. When the
   // completion token is asio::use_future it would be std::future<void>.
   //
   // In C++14 we can omit the return type as it is automatically deduced from
   // the return type of asio::async_initiate.
 {
   // 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)
   //
   // 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,
       std::unique_ptr<std::string> encoded_message, std::size_t repeat_count,
       std::unique_ptr<asio::steady_timer> delay_timer)
   {
     // In this example, the composed operation's intermediate completion
     // handler is implemented as a hand-crafted function object.
     struct intermediate_completion_handler
     {
       // The intermediate completion handler holds a reference to the socket as
       // it is used for multiple async_write operations, as well as for
       // obtaining the I/O executor (see get_executor below).
       tcp::socket& socket_;

       // The allocated buffer for the encoded message. The std::unique_ptr
       // smart pointer is move-only, and as a consequence our intermediate
       // completion handler is also move-only.
       std::unique_ptr<std::string> encoded_message_;

       // The repeat count remaining.
       std::size_t repeat_count_;

       // A steady timer used for introducing a delay.
       std::unique_ptr<asio::steady_timer> delay_timer_;

       // To manage the cycle between the multiple underlying asychronous
       // operations, our intermediate completion handler is implemented as a
       // state machine.
       enum { starting, waiting, writing } state_;

       // As our composed operation performs multiple underlying I/O operations,
       // we should maintain a work object against the I/O executor. This tells
       // the I/O executor that there is still more work to come in the future.
       typename std::decay<decltype(asio::prefer(
             std::declval<tcp::socket::executor_type>(),
             asio::execution::outstanding_work.tracked))>::type io_work_;

       // The user-supplied completion handler, called once only on completion
       // of the entire composed operation.
       typename std::decay<decltype(completion_handler)>::type handler_;

       // By having a default value for the second argument, this function call
       // operator matches the completion signature of both the async_write and
       // steady_timer::async_wait operations.
       void operator()(const std::error_code& error, std::size_t = 0)
       {
         if (!error)
         {
           switch (state_)
           {
           case starting:
           case writing:
             if (repeat_count_ > 0)
             {
               --repeat_count_;
               state_ = waiting;
               delay_timer_->expires_after(std::chrono::seconds(1));
               delay_timer_->async_wait(std::move(*this));
               return; // Composed operation not yet complete.
             }
             break; // Composed operation complete, continue below.
           case waiting:
             state_ = writing;
             asio::async_write(socket_,
                 asio::buffer(*encoded_message_), std::move(*this));
             return; // Composed operation not yet complete.
           }
         }

         // This point is reached only on completion of the entire composed
         // operation.

         // Deallocate the encoded message before calling the user-supplied
         // completion handler.
         encoded_message_.reset();

         // Call the user-supplied handler with the result of the operation.
         handler_(error);
       }

       // It is essential to the correctness of our composed operation that we
       // preserve the executor of the user-supplied completion handler. With a
       // hand-crafted function object we can do this by defining a nested type
       // executor_type and member function get_executor. These obtain the
       // completion handler's associated executor, and default to the I/O
       // executor - in this case the executor of the socket - if the completion
       // handler does not have its own.
       using executor_type = asio::associated_executor_t<
           typename std::decay<decltype(completion_handler)>::type,
           tcp::socket::executor_type>;

       executor_type get_executor() const noexcept
       {
         return asio::get_associated_executor(
             handler_, socket_.get_executor());
       }

       // Although not necessary for correctness, we may also preserve the
       // allocator of the user-supplied completion handler. This is achieved by
       // defining a nested type allocator_type and member function
       // get_allocator. These obtain the completion handler's associated
       // allocator, and default to std::allocator<void> if the completion
       // handler does not have its own.
       using allocator_type = asio::associated_allocator_t<
           typename std::decay<decltype(completion_handler)>::type,
           std::allocator<void>>;

       allocator_type get_allocator() const noexcept
       {
         return asio::get_associated_allocator(
             handler_, std::allocator<void>{});
       }
     };

     // Initiate the underlying async_write operation using our intermediate
     // completion handler.
     auto encoded_message_buffer = asio::buffer(*encoded_message);
     asio::async_write(socket, encoded_message_buffer,
         intermediate_completion_handler{
           socket, std::move(encoded_message),
           repeat_count, std::move(delay_timer),
           intermediate_completion_handler::starting,
           asio::prefer(socket.get_executor(),
               asio::execution::outstanding_work.tracked),
           std::forward<decltype(completion_handler)>(completion_handler)});
   };

   // Encode the message and copy it into an allocated buffer. The buffer will
   // be maintained for the lifetime of the composed asynchronous operation.
   std::ostringstream os;
   os << message;
   std::unique_ptr<std::string> encoded_message(new std::string(os.str()));

   // Create a steady_timer to be used for the delay between messages.
   std::unique_ptr<asio::steady_timer> delay_timer(
       new asio::steady_timer(socket.get_executor()));

   // 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)>(
       initiation, token, std::ref(socket),
       std::move(encoded_message), repeat_count,
       std::move(delay_timer));
 }

 //------------------------------------------------------------------------------

 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_messages(socket, "Testing callback\r\n", 5,
       [](const std::error_code& error)
       {
         if (!error)
         {
           std::cout << "Messages sent\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<void> f = async_write_messages(
       socket, "Testing future\r\n", 5, asio::use_future);

   io_context.run();

   try
   {
     // Get the result of the operation.
     f.get();
     std::cout << "Messages sent\n";
   }
   catch (const std::exception& e)
   {
     std::cout << "Error: " << e.what() << "\n";
   }
 }

 //------------------------------------------------------------------------------

 int main()
 {
   test_callback();
   test_future();
 }
	//
	// composed_6.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/executor_work_guard.hpp>
	#include <asio/io_context.hpp>
	#include <asio/ip/tcp.hpp>
	#include <asio/steady_timer.hpp>
	#include <asio/use_future.hpp>
	#include <asio/write.hpp>
	#include <functional>
	#include <iostream>
	#include <memory>
	#include <sstream>
	#include <string>
	#include <type_traits>
	#include <utility>

	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 composed operation shows composition of multiple underlying operations.
	// It automatically serialises a message, using its I/O streams insertion
	// operator, before sending it N times on the socket. To do this, it must
	// allocate a buffer for the encoded message and ensure this buffer's validity
	// until all underlying async_write operation complete. A one second delay is
	// inserted prior to each write operation, using a steady_timer.

	template <typename T, typename CompletionToken>
	auto async_write_messages(tcp::socket& socket,
	const T& message, std::size_t repeat_count,
	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 always void.
	// In this example, when the completion token is asio::yield_context
	// (used for stackful coroutines) the return type would be also be void, as
	// there is no non-error argument to the completion handler. When the
	// completion token is asio::use_future it would be std::future<void>.
	//
	// In C++14 we can omit the return type as it is automatically deduced from
	// the return type of asio::async_initiate.
	{
	// 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)
	//
	// 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,
	std::unique_ptr<std::string> encoded_message, std::size_t repeat_count,
	std::unique_ptr<asio::steady_timer> delay_timer)
	{
	// In this example, the composed operation's intermediate completion
	// handler is implemented as a hand-crafted function object.
	struct intermediate_completion_handler
	{
	// The intermediate completion handler holds a reference to the socket as
	// it is used for multiple async_write operations, as well as for
	// obtaining the I/O executor (see get_executor below).
	tcp::socket& socket_;

	// The allocated buffer for the encoded message. The std::unique_ptr
	// smart pointer is move-only, and as a consequence our intermediate
	// completion handler is also move-only.
	std::unique_ptr<std::string> encoded_message_;

	// The repeat count remaining.
	std::size_t repeat_count_;

	// A steady timer used for introducing a delay.
	std::unique_ptr<asio::steady_timer> delay_timer_;

	// To manage the cycle between the multiple underlying asychronous
	// operations, our intermediate completion handler is implemented as a
	// state machine.
	enum { starting, waiting, writing } state_;

	// As our composed operation performs multiple underlying I/O operations,
	// we should maintain a work object against the I/O executor. This tells
	// the I/O executor that there is still more work to come in the future.
	typename std::decay<decltype(asio::prefer(
	std::declval<tcp::socket::executor_type>(),
	asio::execution::outstanding_work.tracked))>::type io_work_;

	// The user-supplied completion handler, called once only on completion
	// of the entire composed operation.
	typename std::decay<decltype(completion_handler)>::type handler_;

	// By having a default value for the second argument, this function call
	// operator matches the completion signature of both the async_write and
	// steady_timer::async_wait operations.
	void operator()(const std::error_code& error, std::size_t = 0)
	{
	if (!error)
	{
	switch (state_)
	{
	case starting:
	case writing:
	if (repeat_count_ > 0)
	{
	--repeat_count_;
	state_ = waiting;
	delay_timer_->expires_after(std::chrono::seconds(1));
	delay_timer_->async_wait(std::move(*this));
	return; // Composed operation not yet complete.
	}
	break; // Composed operation complete, continue below.
	case waiting:
	state_ = writing;
	asio::async_write(socket_,
	asio::buffer(encoded_message_), std::move(this));
	return; // Composed operation not yet complete.
	}
	}

	// This point is reached only on completion of the entire composed
	// operation.

	// Deallocate the encoded message before calling the user-supplied
	// completion handler.
	encoded_message_.reset();

	// Call the user-supplied handler with the result of the operation.
	handler_(error);
	}

	// It is essential to the correctness of our composed operation that we
	// preserve the executor of the user-supplied completion handler. With a
	// hand-crafted function object we can do this by defining a nested type
	// executor_type and member function get_executor. These obtain the
	// completion handler's associated executor, and default to the I/O
	// executor - in this case the executor of the socket - if the completion
	// handler does not have its own.
	using executor_type = asio::associated_executor_t<
	typename std::decay<decltype(completion_handler)>::type,
	tcp::socket::executor_type>;

	executor_type get_executor() const noexcept
	{
	return asio::get_associated_executor(
	handler_, socket_.get_executor());
	}

	// Although not necessary for correctness, we may also preserve the
	// allocator of the user-supplied completion handler. This is achieved by
	// defining a nested type allocator_type and member function
	// get_allocator. These obtain the completion handler's associated
	// allocator, and default to std::allocator<void> if the completion
	// handler does not have its own.
	using allocator_type = asio::associated_allocator_t<
	typename std::decay<decltype(completion_handler)>::type,
	std::allocator<void>>;

	allocator_type get_allocator() const noexcept
	{
	return asio::get_associated_allocator(
	handler_, std::allocator<void>{});
	}
	};

	// Initiate the underlying async_write operation using our intermediate
	// completion handler.
	auto encoded_message_buffer = asio::buffer(*encoded_message);
	asio::async_write(socket, encoded_message_buffer,
	intermediate_completion_handler{
	socket, std::move(encoded_message),
	repeat_count, std::move(delay_timer),
	intermediate_completion_handler::starting,
	asio::prefer(socket.get_executor(),
	asio::execution::outstanding_work.tracked),
	std::forward<decltype(completion_handler)>(completion_handler)});
	};

	// Encode the message and copy it into an allocated buffer. The buffer will
	// be maintained for the lifetime of the composed asynchronous operation.
	std::ostringstream os;
	os << message;
	std::unique_ptr<std::string> encoded_message(new std::string(os.str()));

	// Create a steady_timer to be used for the delay between messages.
	std::unique_ptr<asio::steady_timer> delay_timer(
	new asio::steady_timer(socket.get_executor()));

	// 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)>(
	initiation, token, std::ref(socket),
	std::move(encoded_message), repeat_count,
	std::move(delay_timer));
	}

	//------------------------------------------------------------------------------

	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_messages(socket, "Testing callback\r\n", 5,
	[](const std::error_code& error)
	{
	if (!error)
	{
	std::cout << "Messages sent\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<void> f = async_write_messages(
	socket, "Testing future\r\n", 5, asio::use_future);

	io_context.run();

	try
	{
	// Get the result of the operation.
	f.get();
	std::cout << "Messages sent\n";
	}
	catch (const std::exception& e)
	{
	std::cout << "Error: " << e.what() << "\n";
	}
	}

	//------------------------------------------------------------------------------

	int main()
	{
	test_callback();
	test_future();
	}