[/
/ Copyright (c) 2003-2025 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)
/]
[section:deferred Deferred Operations]
The [link asio.reference.deferred `deferred`], completion token takes a call to
an asynchronous operation's initiating function and turns it into a function
object that accepts a completion token. For example:
auto deferred_op =
timer.async_wait(
asio::deferred);
...
std::move(deferred_op)(
[](asio::error_code ec){ ... });
or:
auto deferred_op =
timer.async_wait(
asio::deferred);
...
std::future<void> =
std::move(deferred_op)(
asio::use_future);
The deferred token also supports chaining, to create simple compositions:
auto deferred_op =
timer.async_wait(
asio::deferred(
[&](asio::error_code ec)
{
timer.expires_after(
std::chrono::seconds(1));
return timer.async_wait(
asio::deferred);
});
...
std::future<void> = std::move(deferred_op)(asio::use_future);
[heading Deferred as the Default Completion Token]
Most asynchronous operations provided by Asio have a default completion token.
Although this default token can be changed by specifying a custom executor, it
is normally asio::deferred. This means that we can omit the token and simply
write:
auto deferred_op = timer.async_wait();
[heading See Also]
[link asio.reference.deferred deferred],
[link asio.reference.deferred_t deferred_t],
[link asio.examples.cpp14_examples.deferred Deferred examples (C++11)],
[link asio.examples.cpp14_examples.deferred Deferred examples (C++14)].
[endsect]
