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Subject: [boost] [chrono] [thread] boost.chrono changes to boost::condition_variables
From: Morgan Henry (Morgan.Henry_at_[hidden])
Date: 2010-07-22 10:34:39


I've been exploring the boost.chrono candidate library as a basis for some fixes to boost::condition_variables::timed_wait().

I have some questions:
1) What is the current state of the chrono library, and its likely path into boost?
2) Are the chrono API changes to boost::condition_variables likely to be accepted into the boost.thread library in their current form?
    (i.e introduction of wait_for(), wait_until(), and the introduction of a new explicit dependency from boost/thread/condition_variables on chrono::time_point etc...)
3) Are there any other planned changes to boost::condition_variables::timed_wait to allow use of POSIX clocks other than CLOCK_REALTIME?

My ultimate goal is to provide an implementation of boost::condition_variables that allows access to the POSIX clock CLOCK_MONOTONIC
for use through boost::condition_variables::timed_wait().
Specifically, providing an implementation that uses
    pthread_condattr_setclock(&attr, CLOCK_MONOTONIC) at boost::condition_variables initialisation,
and use of
    pthread_cond_timedwait(..., &t) with clock_gettime(CLOCK_MONOTONIC, &t) in boost::condition_variables::timed_wait() and friends
This change would provide reasonable behaviour of boost::condition_variables::time_wait() in presence of ongoing changes to the system clock.

boost.chrono contributes to this goal by providing a clock abstraction and accessors to the appropriate POSIX clocks through
class monotonic_clock, class system_clock, etc...

Further to this, changes to boost::condition_variable::timed_wait() and similar would be required to use
clock_gettime(CLOCK_MONOTONIC, &t) rather than boost::get_system_time() for calculations when the monotonic_clock is specified.

I'm currently considering whether to trust that the boost.chrono API changes to the boost::condition_variables API are robust, and likely to
persist for the future. Or to propose alternative changes localised to boost::condition_variables that achieve the goals above without the
strong dependency on boost.chrono.

Thanks for any comments or information about the above.
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