boost::deadline_timer can fail when system clock is modified

Question

As could be read at:

https://svn.boost.org/trac/boost/ticket/3504

a deadline_timer that timeouts periodically and which is implemented using deadline_timer::expires_at() (like the example in Boost Timer Tutorial, 3th example) will probably fail if the system time is modified (for example, using the date command, if your operating system is Linux).

Is there a simple and appropiate way of performing this operation now, using Boost? I do not want to use deadline_timer::expires_from_now() because I could verify that it is less accurate than "manually" updating the expiry time.

As a temporal solution I decide to, before setting a new expires_at value, calculate the time period between now() and expires_at(). If it is more than double the periodic delay, then I exceptionally use expires_from_now() to resync with the new absolute time.

Answer 1

In Boost 1.49+, Boost.Asio provides steady_timer. This timer uses chrono::steady_clock, a monotonic clocks that is not affected by changes to the system clock.

If you cannot use Boost 1.49+, then checking the timers or clocks for changes is a reasonable alternative solution. While it is an implementation detail, Boost.Asio may limit the amount of time spent waiting on an event in its reactor, so that it can periodically detect changes to system time. For example, the reactor implementation using epoll will wait a maximum of 5 minutes. Thus, without forcing an interrupt on the reactor (such as setting a new expiration time on a timer), it can take Boost.Asio up to 5 minutes before detecting changes to system time.