Using boost asio 1.47, suse linux 11.3, gcc 4.5 I am using boost::asio::deadline_timer, where the timer fires every second. When the timer expires, I check responses from the clients. I use the same timer to check when I have reach the minute boundary, so that server can do some other work.
Now 99.9% of the time this works perfectly. However occasionally the timer does not fire every second, in fact it can delay/block for several minutes!
FWIW, I'm using asio:deadline_timer's quite intensively with different resolutions (from tens of ms to tens of sec), and never encountered such an issue. Typically, in my application there're a few tens of timers associated with several io_services (io_service-per-cpu approach) with different deadlines, and all of them fire as expected. Check that you never block any completion-handler (timed locks, time-consuming processing etc). Besides, try upgrading to the most recent asio (see revision history: http://www.boost.org/doc/libs/1_52_0/doc/html/boost_asio/history.html) By the way, is it possible that the above 0.1% happens when the system time gets updated (eg. due to NTP synchronization)? If yes, see my comments below.
o Are there known problems with boost::asio::deadline_timer accuracy I realise I need soft real time, with one minute resolution.
At these resolutions there shouldn't be any problem. It has monotonicity issues, which are solved in 1.49 by steady_timer, but if you don't update the system-time it shouldn't affect you. (See the following: http://permalink.gmane.org/gmane.comp.lib.boost.asio.user/5183)
o Should I have two separate timers, one 1 second & for 1 minute
After the timer expires and the completion handler gets called, you can re-set the same timer with any other deadline.
o Is using timer_.expires_at(...) more reliable, I assume this affects how it configures timerfd_settime
As far as I can see, expires_from_now() is implemented in terms of expires_at(), so there's no any difference. Igor'.