[/ / Copyright (c) 2003-2020 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:timers Timers] Long running I/O operations will often have a deadline by which they must have completed. These deadlines may be expressed as absolute times, but are often calculated relative to the current time. As a simple example, to perform a synchronous wait operation on a timer using a relative time one may write: io_context i; ... deadline_timer t(i); t.expires_from_now(boost::posix_time::seconds(5)); t.wait(); More commonly, a program will perform an asynchronous wait operation on a timer: void handler(boost::system::error_code ec) { ... } ... io_context i; ... deadline_timer t(i); t.expires_from_now(boost::posix_time::milliseconds(400)); t.async_wait(handler); ... i.run(); The deadline associated with a timer may also be obtained as a relative time: boost::posix_time::time_duration time_until_expiry = t.expires_from_now(); or as an absolute time to allow composition of timers: deadline_timer t2(i); t2.expires_at(t.expires_at() + boost::posix_time::seconds(30)); [heading See Also] [link boost_asio.reference.basic_deadline_timer basic_deadline_timer], [link boost_asio.reference.deadline_timer deadline_timer], [link boost_asio.tutorial.tuttimer1 timer tutorials]. [endsect]