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add MonotonicTimer#1003

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flixr wants to merge 1 commit intoros:lunar-develfrom
flixr:monotonic_timer
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add MonotonicTimer#1003
flixr wants to merge 1 commit intoros:lunar-develfrom
flixr:monotonic_timer

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@flixr flixr commented Feb 26, 2017

based on MonotonicTime (which uses the CLOCK_MONOTONIC).
This timer is not influenced by time jumps of the system time,
so ideal for things like periodic checks of timeout/heartbeat, etc...

Depends on ros/roscpp_core#55

This was referenced Feb 26, 2017
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add MonotonicTimer
baa3dc4 
based on MonotonicTime (which uses the CLOCK_MONOTONIC).
This timer is not influenced by time jumps of the system time,
so ideal for things like periodic checks of timeout/heartbeat, etc...
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flixr commented Feb 27, 2017

So while in theory this should work well, it seems that there is a bug in the boost condition timed_wait:
Even if you pass it a duration it will simply add it to the current system time and wait until then.
It seems to be fixed in boost 1.61 if you specify BOOST_THREAD_HAS_CONDATTR_SET_CLOCK_MONOTONIC, see https://svn.boost.org/trac/boost/ticket/6377

So that means that currently the MonotonicTimer can nicely deal with forward jumps in time, but not with backwards jumps.

Possible solutions:

  • also only wait for 1ms just like in the sim time case and re-check the sleep_end predicate
    • drawback is that you up a lot more often than needed
    • to do this only for the MonotonicTimer we either need to add a member function isMonotonicTime or use a typeid check?
  • replace the boost condition variable with C++11 equivalent where you can specify it to use a monotonic clock

@flixr flixr mentioned this pull request Mar 6, 2017
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flixr commented Mar 6, 2017

Closing in favor of #1014

@flixr flixr closed this Mar 6, 2017
@flixr flixr deleted the monotonic_timer branch March 6, 2017 16:16
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