Re: [Boost-users] boost asio: boost::asio::deadline_timer blocking ?

Subject: Re: [Boost-users] boost asio: boost::asio::deadline_timer blocking ?
From: Igor R (boost.lists_at_[hidden])
Date: 2012-11-09 06:44:01

> 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'.