Difference between `deadline_timer`and `waitable_timer` in `boost asio`
To expire a timer in 5 seconds,
is there any practical difference between these two?
Is any one preferable(performance, resource, etc.) to the other for this case?
[Option 1] deadline_timer:
boost::asio::deadline_timer timer(io_service);
timer.expires_from_now(boost::posix_time::seconds(5));
[Option 2] waitable_timer(system_timer or steady_timer):
boost::asio::system_timer timer(io_service);
timer.expires_from_now(std::chrono::seconds(5));
PS: Please concentrate on comparing deadline_timer vs. system_timer, rather than system_timer vs. steady_timer.
Answer
The only difference is between clock types used.
As of Boost 1.56, both basic_deadline_timer and basic_waitable_timer use detail::deadline_timer_service inside.
There's no difference in how it performs waiting, the only difference is in how it performs time calculation.
In its wait() method it uses Time_Traits::now() to check if it needs to wait more. For system_timer it's std::chrono::system_clock::now(), and for deadline_timer it's boost::posix_time::microsec_clock::universal_time() or boost::posix_time::second_clock::universal_time() depending on the presence of high precision clock (see time_traits.hpp).
std::chrono::system_clock implementation is provided by a compiler/standard library vendor, whereas boost::posix_time::*clock is implemented by Boost using available system functions.
These implementations of course may have different performance and/or precision depending on the platform and the compiler.